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Credentials

Awards & Distinctions ?

Awards  
Compassionate Doctor Recognition (2011, 2013)

Affiliations ?

Dr. Buchanan is affiliated with 8 hospitals.

Hospital Affiliations

Score

Rankings

  • Shands at Starke
    922 E Call St, Starke, FL 32091
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    Top 25%
  • North Florida Regional Medical Center
    6500 W Newberry Rd, Gainesville, FL 32605
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    Top 25%
  • Shands Hospital at The Univ. of Florida
    1600 Sw Archer Rd, Gainesville, FL 32610
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    Top 25%
  • Shands at Lake Shore
    368 NE Franklin St, Lake City, FL 32055
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  • Shands at AGH
    Obstetrician & Gynecologist
    801 SW 2nd Ave, Gainesville, FL 32601
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  • Shands at Live Oak
    1600 Sw Archer Rd, Gainesville, FL 32610
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  • Shands A G H, Gainesville, Fl
  • Shands at UF
  • Publications & Research

    Dr. Buchanan has contributed to 98 publications.
    Title Androgen Receptor and Nutrient Signaling Pathways Coordinate the Demand for Increased Amino Acid Transport During Prostate Cancer Progression.
    Date March 2012
    Journal Cancer Research
    Excerpt

    L-Type amino acid transporters such as LAT1 and LAT3 mediate the uptake of essential amino acids. Here, we report that prostate cancer cells coordinate the expression of LAT1 and LAT3 to maintain sufficient levels of leucine needed for mTORC1 signaling and cell growth. Inhibiting LAT function was sufficient to decrease cell growth and mTORC1 signaling in prostate cancer cells. These cells maintained levels of amino acid influx through androgen receptor-mediated regulation of LAT3 expression and ATF4 regulation of LAT1 expression after amino acid deprivation. These responses remained intact in primary prostate cancer, as indicated by high levels of LAT3 in primary disease, and by increased levels of LAT1 after hormone ablation and in metastatic lesions. Taken together, our results show how prostate cancer cells respond to demands for increased essential amino acids by coordinately activating amino acid transporter pathways vital for tumor outgrowth.

    Title Global Levels of Specific Histone Modifications and an Epigenetic Gene Signature Predict Prostate Cancer Progression and Development.
    Date February 2011
    Journal Cancer Epidemiology, Biomarkers & Prevention : a Publication of the American Association for Cancer Research, Cosponsored by the American Society of Preventive Oncology
    Excerpt

    Epigenetic alterations are common in prostate cancer, yet how these modifications contribute to carcinogenesis is poorly understood. We investigated whether specific histone modifications are prognostic for prostate cancer relapse, and whether the expression of epigenetic genes is altered in prostate tumorigenesis.

    Title Lack of Correlation Between Epidermal Growth Factor Receptor Status and Response to Panitumumab Monotherapy in Metastatic Colorectal Cancer.
    Date August 2010
    Journal Clinical Cancer Research : an Official Journal of the American Association for Cancer Research
    Excerpt

    Panitumumab, a fully human anti-epidermal growth factor receptor (EGFR) monoclonal antibody, is approved as monotherapy for the treatment of metastatic colorectal cancer. We evaluated the association of tumor EGFR expression levels with outcomes in patients with chemorefractory metastatic colorectal cancer.

    Title Serum Testosterone Bioassay Evaluation in a Large Male Cohort.
    Date March 2010
    Journal Clinical Endocrinology
    Excerpt

    To assess if a cell-based readout of androgen action in serum demonstrates a closer association with recognized classical parameters of androgen action in men than current measures of serum testosterone (T).

    Title A Novel Androgen Receptor Amino Terminal Region Reveals Two Classes of Amino/carboxyl Interaction-deficient Variants with Divergent Capacity to Activate Responsive Sites in Chromatin.
    Date June 2009
    Journal Endocrinology
    Excerpt

    The androgen receptor (AR) is an important signaling molecule in multiple tissues, yet its mode of action and cell-specific activities remain enigmatic. AR function has been best studied in the prostate, in which it is essential for growth and homeostasis of the normal organ as well as each stage of cancer development. Investigation of mechanisms responsible for continued AR action that evolve during prostate cancer progression or after hormonal management of the disease have been instructive in defining AR signaling pathways. In the current paper, we use sequence similarity and the collocation of somatic mutations in prostate cancer to define residues 501-535 of the AR amino-terminal domain as an important mediator of receptor function. Specifically, the 501-535 region is required for optimal interaction of the amino-terminal domain with both the p160 coactivator, nuclear receptor coactivator-2, and the AR-ligand binding domain in the amino/carboxyl (N/C) interaction. The N/C interaction is decreased by deletion of the 501-535 region but is distinct from deletion of the (23)FQNLF(27) peptide in that it does not affect the capacity of the AR to activate transcription from a chromatin integrated reporter or recruitment of the receptor to androgen-responsive loci in vivo. Collectively, we have been able to outline two classes of N/C-deficient AR variant that are divergent in their capacity to act in a chromatin context, thereby further defining the interplay between N/C interaction and coregulator recruitment via multiple receptor domains. These mechanisms are likely to be key determinants of the cell and promoter specific activities of the AR.

    Title Control of Androgen Receptor Signaling in Prostate Cancer by the Cochaperone Small Glutamine Rich Tetratricopeptide Repeat Containing Protein Alpha.
    Date December 2007
    Journal Cancer Research
    Excerpt

    Although the androgen receptor (AR) is accepted as the major determinant of prostate cancer cell survival throughout disease progression, it is currently unclear how the receptor sustains genomic signaling under conditions of systemic androgen ablation. Here, we show that the evolutionarily conserved Hsp70/Hsp90 cochaperone, small glutamine-rich tetratricopeptide repeat containing protein alpha (alphaSGT), interacts with the hinge region of the human AR in yeast and mammalian cells. Overexpression and RNA interference revealed that alphaSGT acts to (a) promote cytoplasmic compartmentalization of the AR, thereby silencing the receptors basal/ligand-independent transcriptional activity, (b) regulate the sensitivity of receptor signaling by androgens, and (c) limit the capacity of noncanonical ligands to induce AR agonist activity. Immunofluorescence, coactivator, and chromatin immunoprecipitation analyses strongly suggest that these effects of alphaSGT on AR function are mediated by interaction in the cytoplasm and are distinct from the receptors response to classic coregulators. Quantitative immunohistochemical analysis of alphaSGT and AR levels in a cohort of 32 primary and 64 metastatic human prostate cancers revealed dysregulation in the level of both proteins during disease progression. The significantly higher AR/alphaSGT ratio in metastatic samples is consistent with the sensitization of prostate tumor cells to androgen signaling with disease progression, particularly in a low-hormone environment. These findings implicate alphaSGT as a molecular rheostat of in vivo signaling competence by the AR, and provide new insight into the determinants of androgen sensitivity during prostate cancer progression.

    Title Identification of Novel Androgen Receptor Target Genes in Prostate Cancer.
    Date August 2007
    Journal Molecular Cancer
    Excerpt

    BACKGROUND: The androgen receptor (AR) plays critical roles in both androgen-dependent and castrate-resistant prostate cancer (PCa). However, little is known about AR target genes that mediate the receptor's roles in disease progression. RESULTS: Using Chromatin Immunoprecipitation (ChIP) Display, we discovered 19 novel loci occupied by the AR in castrate resistant C4-2B PCa cells. Only four of the 19 AR-occupied regions were within 10-kb 5'-flanking regulatory sequences. Three were located up to 4-kb 3' of the nearest gene, eight were intragenic and four were in gene deserts. Whereas the AR occupied the same loci in C4-2B (castrate resistant) and LNCaP (androgen-dependent) PCa cells, differences between the two cell lines were observed in the response of nearby genes to androgens. Among the genes strongly stimulated by DHT in C4-2B cells--D-dopachrome tautomerase (DDT), Protein kinase C delta (PRKCD), Glutathione S- transferase theta 2 (GSTT2), Transient receptor potential cation channel subfamily V member 3 (TRPV3), and Pyrroline-5-carboxylate reductase 1 (PYCR1)--most were less strongly or hardly stimulated in LNCaP cells. Another AR target gene, ornithine aminotransferase (OAT), was AR-stimulated in a ligand-independent manner, since it was repressed by AR siRNA knockdown, but not stimulated by DHT. We also present evidence for in vivo AR-mediated regulation of several genes identified by ChIP Display. For example, PRKCD and PYCR1, which may contribute to PCa cell growth and survival, are expressed in PCa biopsies from primary tumors before and after ablation and in metastatic lesions in a manner consistent with AR-mediated stimulation. CONCLUSION: AR genomic occupancy is similar between LNCaP and C4-2B cells and is not biased towards 5' gene flanking sequences. The AR transcriptionally regulates less than half the genes nearby AR-occupied regions, usually but not always, in a ligand-dependent manner. Most are stimulated and a few are repressed. In general, response is stronger in C4-2B compared to LNCaP cells. Some of the genes near AR-occupied regions appear to be regulated by the AR in vivo as evidenced by their expression levels in prostate cancer tumors of various stages. Several AR target genes discovered in the present study, for example PRKCD and PYCR1, may open avenues in PCa research and aid the development of new approaches for disease management.

    Title Hdlalert - a Healthcare Dl Alerting System: from User Needs to Implementation.
    Date February 2007
    Journal Health Informatics Journal
    Excerpt

    In the health domain, there are many circumstances where clinicians (i.e. doctors, nurses, allied health professionals) and patients wish to track changes in medical knowledge. However, existing 'news' or 'alert' services provide relatively limited means for selecting which information to receive. The result is that clinicians and patients often receive information that is inappropriate, irrelevant or simply too much. In this paper, we detail alert-relevant findings from several international user studies (e.g. UK, Germany and New Zealand) incorporating both clinical staff (across several hospitals) and patients' perceptions. These findings demonstrate the importance of context, in terms of both the user's task and immediate environment. We introduce a novel alerting architecture that can provide a finely tailored stream of alerts to the user, and provides further support to assist the interpretation of received material.

    Title Cysteine-scanning Mutagenesis and Disulfide Mapping Studies of the Conserved Domain of the Twin-arginine Translocase Tatb Component.
    Date December 2006
    Journal The Journal of Biological Chemistry
    Excerpt

    The cytoplasmic membrane protein TatB is an essential component of the Escherichia coli twin-arginine (Tat) protein translocation pathway. Together with the TatC component it forms a complex that functions as a membrane receptor for substrate proteins. Structural predictions suggest that TatB is anchored to the membrane via an N-terminal transmembrane alpha-helix that precedes an amphipathic alpha-helical section of the protein. From truncation analysis it is known that both these regions of the protein are essential for function. Here we construct 31 unique cysteine substitutions in the first 42 residues of TatB. Each of the substitutions results in a TatB protein that is competent to support Tat-dependent protein translocation. Oxidant-induced disulfide cross-linking shows that both the N-terminal and amphipathic helices form contacts with at least one other TatB protomer. For the transmembrane helix these contacts are localized to one face of the helix. Molecular modeling and molecular dynamics simulations provide insight into the possible structural basis of the transmembrane helix interactions. Using variants with double cysteine substitutions in the transmembrane helix, we were able to detect cross-links between up to five TatB molecules. Protein purification showed that species containing at least four cross-linked TatB molecules are found in correctly assembled TatBC complexes. Our results suggest that the transmembrane helices of TatB protomers are in the center rather than the periphery of the TatBC complex.

    Title Suppression of Androgen Receptor Signaling in Prostate Cancer Cells by an Inhibitory Receptor Variant.
    Date July 2006
    Journal Molecular Endocrinology (baltimore, Md.)
    Excerpt

    There is increasing evidence that sensitization of the androgen receptor (AR) signaling pathway contributes to the failure of androgen ablation therapy for prostate cancer, and that direct targeting of the AR may be a useful therapeutic approach. To better understand how AR function could be abrogated in prostate cancer cells, we have developed a series of putative dominant-negative variants of the human AR, containing deletions or mutations in activation functions AF-1, AF-5, and/or AF-2. One construct, AR inhibitor (ARi)-410, containing a deletion of AF-1 and part of AF-5 of the AR, had no intrinsic transactivation activity but inhibited wild-type AR (wtAR) in a ligand-dependent manner by at least 95% when transfected at a 4:1 molar ratio. ARi-410 was an equally potent inhibitor of gain-of-function AR variants. Ectopic expression of ARi-410 inhibited the proliferation of AR-positive LNCaP cells, but not AR-negative PC-3 cells. Whereas ARi-410 also marginally inhibited progesterone receptor activity, this was far less pronounced than the effect on AR (50% vs. 95% maximal inhibition, respectively), and there was no inhibition of either vitamin D or estrogen receptor activity. In the presence of ligand, ARi-410 interacted with wtAR, and both receptors translocated into the nucleus. Whereas the amino-carboxy terminal interaction was not necessary for optimal dominant-negative activity, disruption of dimerization through the ligand binding domain reduced the efficacy of ARi-410. In addition, although inhibition of AR function by ARi-410 was not dependent on DNA binding, the DNA binding domain was required for dominant-negative activity. Taken together, our results suggest that interaction between ARi-410 and the endogenous AR in prostate cancer cells, potentially through the DNA binding and ligand binding domains, results in a functionally significant reduction in AR signaling and AR-dependent cell growth.

    Title Intellectual and Functional Outcome of Children 3 Years Old or Younger Who Have Cns Malignancies.
    Date November 2005
    Journal Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology
    Excerpt

    PURPOSE: To evaluate the impact of tumor location, clinical parameters, and therapy on neurocognitive, neuroendocrine, and functional outcomes in children < or = 3 years old with intracranial CNS malignancies who survived at least 2 years after diagnosis. PATIENTS AND METHODS: Records were retrospectively reviewed for 194 children diagnosed from 1985 to 1999 at St Jude Children's Research Hospital (Memphis, TN). RESULTS: The median age at diagnosis was 1.8 years (range, 0.1 to 3.5 years). Median follow-up was 7.64 years (2.0 to 19.4 years). Tumors were infratentorial (102), diencephalic (53), and hemispheric (39); 47% required ventriculoperitoneal shunts, 36% developed seizure disorders, and 20% developed severe ototoxicity. Therapy included no radiation therapy (RT) in 57 (30%), local RT in 87 (45%), and craniospinal irradiation (CSI) in 49 (25%). Overall survival at 10 years was 78 +/- 4%. In a longitudinal analysis of 126 patients with at least one neurocognitive evaluation (NE), the mean rate of intelligence quotient (IQ) change for patients who received CSI (-1.34 points per year) and local RT (-0.51 points per year) was significantly different from the no RT group (0.91 points per year; P = .005 and P = .036, respectively). Patients with hemispheric tumors had a significantly greater IQ decline (-1.52 points per year) than those with midline tumors (0.59 points per year; P = .038). Among those with NE > or = 5 years after diagnosis, 71.4% of CSI recipients compared with 23% of local RT recipients had IQ less than 70 (P = .021). Patients undergoing CSI were more likely to develop endocrinopathies (P < .0001) and to require special education (P = .0007). CONCLUSION: In young children with CNS tumors, CSI and hemispheric location are associated with significant declines in IQ scores.

    Title Targeting the Androgen Receptor: Improving Outcomes for Castration-resistant Prostate Cancer.
    Date March 2005
    Journal Endocrine-related Cancer
    Excerpt

    The categorization of prostate cancers that are progressing after castration as 'hormone-refractory' evolved from the clinical observation that surgical or medical castration (i.e. androgen ablation therapy; AAT) is not curative and, despite an initial response, virtually all tumors eventually regrow. Successful AAT is contingent on the dependence of prostate cancer cells for androgen signaling through an intracellular mediator, the androgen receptor (AR) for survival. Current preclinical and clinical data imply that the AR is expressed and continues to mediate androgen signaling after failure of AAT. As AAT does not completely eliminate circulating androgens, sufficient concentrations of dihydrotestosterone may accumulate in tumor cells to maintain AR signaling, especially in the context of upregulated receptor levels or increased sensitivity of the AR for activation. In addition, ligands of non-testicular origin or ligand-independent activation can contribute to continued AR signaling. In many cases, therefore, from the perspective of the AR, a 'hormone-refractory' classification after failure of AAT is inappropriate. Classifying prostate tumors that progress after AAT as 'castration-resistant' may be more relevant. Clinical responses to second- and third-line hormonal therapies suggest that the mechanisms of AR activation are in part a function of previously administered AAT. Accordingly, the increasing trend to utilize AAT earlier in the course of the clinical disease may have a greater influence on the genotype and phenotype of the resistant tumor. In this article, we detail strategies to inhibit the growth of prostate cancer cells that specifically target the AR in addition to those practiced traditionally that indirectly target the receptor by reducing the amount of circulating ligand. We propose that treatment regimes combining AAT with direct AR targeting strategies may provide a more complete blockade of androgen signaling, thereby preventing or significantly delaying the emergence of treatment-resistant disease.

    Title Mutation of the Androgen Receptor Causes Oncogenic Transformation of the Prostate.
    Date February 2005
    Journal Proceedings of the National Academy of Sciences of the United States of America
    Excerpt

    Recent evidence demonstrates that the androgen receptor (AR) continues to influence prostate cancer growth despite medical therapies that reduce circulating androgen ligands to castrate levels and/or block ligand binding. Whereas the mutation, amplification, overexpression of AR, or cross-talk between AR and other growth factor pathways may explain the failure of androgen ablation therapies in some cases, there is little evidence supporting a causal role between AR and prostate cancer. In this study, we functionally and directly address the role whereby AR contributes to spontaneous cancer progression by generating transgenic mice expressing (i) AR-WT to recapitulate increased AR levels and ligand sensitivity, (ii) AR-T857A to represent a promiscuous AR ligand response, and (iii) AR-E231G to model altered AR function. Whereas transgenes encoding either AR-WT or AR-T857A did not cause prostate cancer when expressed at equivalent levels, expression of AR-E231G, which carries a mutation in the most highly conserved signature motif of the NH2-terminal domain that also influences interactions with cellular coregulators, caused rapid development of prostatic intraepithelial neoplasia that progressed to invasive and metastatic disease in 100% of mice examined. Taken together, our data now demonstrate the oncogenic potential of steroid receptors and implicate altered AR function and receptor coregulator interaction as critical determinants of prostate cancer initiation, invasion, and metastasis.

    Title A Novel Androgen Receptor Mutant, A748t, Exhibits Hormone Concentration-dependent Defects in Nuclear Accumulation and Activity Despite Normal Hormone-binding Affinity.
    Date June 2003
    Journal Molecular Endocrinology (baltimore, Md.)
    Excerpt

    Functional analysis of androgen receptor (AR) gene mutations isolated from prostate cancer has led to the identification of residues that play important roles in the structure and function of the receptor. Here we report the characteristics of a novel AR mutation A748T located in helix 5 of the ligand-binding domain, which was identified in metastatic prostate cancer. Despite a normal hormone-binding affinity, A748T causes hormone concentration-dependent defects in nuclear accumulation and transcriptional activation. Moreover, when equivalent amounts of DNA are transfected, the mutant is expressed at much lower levels than the wild-type AR (ARWT). Treatment with geldanamycin to disrupt receptor-heat shock protein complexes rapidly decreases the levels of ARWT but not A748T, suggesting that the lower expression and rapid degradation rate of A748T is due to weaker interactions with heat shock proteins. Further analysis revealed that hormone dissociates from A748T five times faster than from ARWT. Loss of the ability to form stable amino/carboxyl-terminal interactions causes accelerated dissociation rates in some AR mutants. However, A748T exhibits normal amino/carboxyl-terminal interactions at high hormone concentrations, suggesting that the mutation alters interactions with ligand. Consistent with this conclusion, our structural model predicts that A748T disrupts crucial contact points with ligand, thereby altering the conformation of the ligand-binding domain.

    Title Effect of Mri on Clinical Outcome of Recurrent Fistula-in-ano.
    Date December 2002
    Journal Lancet
    Excerpt

    Recurrent fistula-in-ano is usually due to sepsis missed at surgery, which can be identified by MRI. We aimed to establish the therapeutic effect of MRI in patients with fistula-in-ano. We did MRI in 71 patients with recurrent fistula, with further surgery done at the discretion of the surgeon. Surgery and MRI agreed in 40 patients, five (13%) of whom had further recurrence, compared with 16 (52%) of 31 in whom surgery and MRI disagreed (p=0.0005). Further recurrence in all 16 was at the site predicted by MRI. For surgeons who always acted on MRI, further recurrences arose in four of 25 (16%) operations versus eight of 14 (57%) operations for those who ignored imaging (p=0.008). Surgery guided by MRI reduces further recurrence of fistula-in-ano by 75% and should be done in all patients with recurrent fistula.

    Title Truncation Analysis of Tata and Tatb Defines the Minimal Functional Units Required for Protein Translocation.
    Date November 2002
    Journal Journal of Bacteriology
    Excerpt

    The TatA and TatB proteins are essential components of the twin arginine protein translocation pathway in Escherichia coli. C-terminal truncation analysis of the TatA protein revealed that a plasmid-expressed TatA protein shortened by 40 amino acids is still fully competent to support protein translocation. Similar truncation analysis of TatB indicated that the final 30 residues of TatB are dispensable for function. Further deletion experiments with TatB indicated that removal of even 70 residues from its C terminus still allowed significant transport. These results imply that the transmembrane and amphipathic helical regions of TatA and TatB are critical for their function but that the C-terminal domains are not essential for Tat transport activity. A chimeric protein comprising the N-terminal region of TatA fused to the amphipathic and C-terminal domains of TatB supports a low level of Tat activity in a strain in which the wild-type copy of either tatA or tatB (but not both) is deleted.

    Title Collocation of Androgen Receptor Gene Mutations in Prostate Cancer.
    Date July 2001
    Journal Clinical Cancer Research : an Official Journal of the American Association for Cancer Research
    Excerpt

    Consistent with both the development of the normal prostate gland and prostate tumorigenesis being dependent on testicular androgens, targeting the androgen-signaling axis (i.e., androgen ablation therapy) remains the predominant treatment regime for patients with metastatic prostate cancer. Although there is a very good initial response to androgen ablation, these treatments are essentially palliative. Recent evidence suggests that treatment failure may not result from a loss of androgen signaling but, rather, from the acquisition of genetic changes that lead to aberrant activation of the androgen-signaling axis. A consistent finding is that androgen receptor (AR) gene mutations, present in metastatic prostate cancer and in human prostate cancer cell lines as well as in xenograft and other animal models, result in decreased specificity of ligand-binding and inappropriate receptor activation by estrogens, progestins, adrenal androgens, glucocorticoids and/or AR antagonists. Because a significant proportion of missense mutations in the AR gene reported in prostate cancer collocate to the signature sequence and AF-2, two discrete regions of the ligand-binding domain critical for androgen signaling, we recently proposed that collocation of mutations identified in prostate cancer would identify additional regions of the AR important in receptor function. This approach led to the identification of a four-amino acid region at the boundary of the hinge and ligand-binding domains of the receptor that forms half of a potential protein-protein binding site. AR gene mutations have also been identified that collocate to areas in the DNA-binding domain, to the NH(2)-terminal transactivation domain, and to the hinge region in prostate tumors. In nearly every case, missense mutations in the AR gene identified in prostate cancer that collocate to discrete regions of the receptor contribute to altered androgen signaling and provide a potential mechanism to explain the reemergence of tumor growth during the course of hormone ablation therapies.

    Title Hormone Status Selects for Spontaneous Somatic Androgen Receptor Variants That Demonstrate Specific Ligand and Cofactor Dependent Activities in Autochthonous Prostate Cancer.
    Date May 2001
    Journal The Journal of Biological Chemistry
    Excerpt

    We have used the autochthonous transgenic adenocarcinoma of mouse prostate (TRAMP) model to investigate the relationship between somatic mutation in the androgen receptor (AR) and the emergence of androgen-independent prostate cancer. Here we report the identification, isolation, and characterization of distinct classes of AR variants from spontaneous prostate tumors in the TRAMP model. Using cDNA cloning, single stranded conformation polymorphism and sequencing strategies, 15 unique somatic mutations in the AR were identified in prostate tumors obtained from eight TRAMP mice between 24 and 29 weeks of age. At least one mutation was isolated from each mouse. All mutations were single base substitutions, 10 were missense and 5 were silent. Nine mutations in the AR were identified in tumors of four mice that were castrated at 12 weeks of age. Interestingly, the majority of mutations (seven out of nine, 78%) identified in the androgen-independent tumors colocalized in the AR transactivation domain. The remaining mutations colocalized in the AR ligand binding domain. In general, the AR variants demonstrated promoter-, cell-, and cofactor-specific activities in response to various hormones. All AR variants isolated in this study maintained strong sensitivity for androgens, and four AR variants isolated from castrated mice demonstrated increased activities in the absence of ligand. The K638M and F677S variants demonstrated increased activities in response to androgen, and K638M also demonstrated increased response to estradiol. In the presence of AR coactivator ARA70 the E231G variant demonstrated increased activity in response to both androgen and estradiol. However, in the presence of AR coactivator ARA160 the E231G variant was selectively responsive to androgen. Collectively these analyses not only indicate that somatic mutations in the AR gene occur spontaneously in TRAMP tumors but also how changes in the hormonal environment may drive the selection of spontaneous somatic mutations that provide a growth advantage.

    Title Mutations at the Boundary of the Hinge and Ligand Binding Domain of the Androgen Receptor Confer Increased Transactivation Function.
    Date February 2001
    Journal Molecular Endocrinology (baltimore, Md.)
    Excerpt

    The androgen receptor (AR), a member of the steroid receptor superfamily of nuclear transcription factors, mediates androgen signaling in diverse target tissues. Here we report AR gene mutations identified in human prostate cancer and the autochthonous transgenic adenocarcinoma of the mouse prostate model that colocate to residues (668)QPIF(671) at the boundary of the hinge and ligand-binding domain, resulting in receptors that exhibit 2- to 4-fold increased activity compared with wild-type AR in response to dihydrotestosterone, estradiol, progesterone, adrenal androgens, and the AR antagonist, hydroxyflutamide, without an apparent effect on receptor levels, ligand binding kinetics, or DNA binding. The expression of these or similar variants could explain the emergence of hormone refractory disease in a subset of patients. Homology modeling indicates that amino acid residues (668)QPIF(671) form a ridge bordering a potential protein-protein interaction surface. The naturally occurring AR gene mutations reported in this study result in decreased hydrophobicity of this surface, suggesting that altered receptor-protein interaction mediates the precocious activity of the AR variants.

    Title Breast Cancer Susceptibility Gene 1 (brcai) is a Coactivator of the Androgen Receptor.
    Date November 2000
    Journal Cancer Research
    Excerpt

    In the present study, the role of BRCA1 in ligand-dependent androgen receptor (AR) signaling was assessed. In transfected prostate and breast cancer cell lines, BRCA1 enhanced AR-dependent transactivation of a probasin-derived reporter gene. The effects of BRCA1 were mediated through the NH2-terminal activation function (AF-1) of the receptor. Cotransfection of p160 coactivators markedly potentiated BRCA1-mediated enhancement of AR signaling. In addition, BRCA1 was shown to interact physically with both the AR and the p160 coactivator, glucocorticoid receptor interacting protein 1. These findings suggest that BRCA1 may directly modulate AR signaling and, therefore, may have implications regarding the proliferation of normal and malignant androgen-regulated tissues.

    Title Neutrophil Pool Sizes and Granulocyte Colony-stimulating Factor Production in Human Mid-trimester Fetuses.
    Date September 1995
    Journal Pediatric Research
    Excerpt

    We quantified neutrophils and neutrophil progenitors, and assessed granulocyte colony-stimulating factor (G-CSF) production in the liver and bone marrow of 20 human abortuses after elective pregnancy termination between 14 and 24 wk of gestation. Mature neutrophils were not observed in any of the liver specimens, but were present in the bone marrow as early as 14 wk. The concentrations of neutrophils in the fetal marrow were extremely low, by comparison with term infants and adults, with less than 5% of the nucleated cells being segmented neutrophils, band neutrophils, or metamyelocytes compared with 31-69% in term infants. Despite the low neutrophil populations, progenitors which had the capacity for clonal maturation into neutrophils in vitro were abundant in the fetal liver and fetal bone marrow. In addition, such progenitors had a dose-response relationship to recombinant G-CSF similar to that of progenitors from the bone marrow of healthy adults. At each gestational age tested, stimulation of mononuclear cells from fetal liver with IL-1 alpha generated less G-CSF protein and fewer G-CSF mRNA transcripts than did stimulation of mononuclear cells from fetal bone marrow. Mononuclear cells from the fetal bone marrow produced less G-CSF protein and mRNA than did mononuclear cells from the blood of adults. Thus, the liver of the mid-trimester human fetus is almost devoid of neutrophils, and the bone marrow contains a significantly lower proportion of neutrophils than does the marrow of term neonates or adults. These findings correlate with IL-1 alpha-induced production of G-CSF in these organs.(ABSTRACT TRUNCATED AT 250 WORDS)

    Title Treatment of Cns Relapse in Children with Acute Lymphoblastic Leukemia: A Pediatric Oncology Group Study.
    Date March 1993
    Journal Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology
    Excerpt

    PURPOSE: To assess the efficacy and toxicity of chemotherapy and cranial radiation for the treatment of children with acute lymphoblastic leukemia (ALL) following first isolated CNS relapse. PATIENTS AND METHODS: One hundred twenty children were treated on Pediatric Oncology Group (POG) protocol 8304. All children had received prophylactic CNS therapy during their initial treatment. The treatment protocol included a four-drug reinduction and six weekly doses of triple intrathecal therapy (TIT). Cranial radiation, 24 Gy, was followed by monthly TIT. Systemic consolidation and maintenance therapy included 6-week cycles of mercaptopurine/methotrexate (6MP/MTX) and vincristine/cyclophosphamide (VCR/CTX), with randomization to intervening pulses of prednisone/doxorubicin (PDN/DOX) or teniposide (VM26)/cytarabine (Ara-C) for a total of 88 weeks. RESULTS: All 120 patients achieved a second complete remission. There have been 61 protocol failures. Thirty-five patients had a bone marrow relapse, four with simultaneous CNS involvement and one with concurrent testicular leukemia. Thirteen patients had a second isolated CNS relapse, 10 a testicular relapse, and two relapsed in other sites. One patient died in remission. Overall event-free survival (EFS) at 4 years was 46% +/- 7%. The toxicity associated with this protocol was minimal except for leukoencephalopathy, which occurred in 20 (17%) patients. The treatment comparison between VM26/Ara-C or PDN/DOX pulses showed a trend toward superior EFS (P = .12) in favor of VM-26/Ara-C. CONCLUSION: To date, this represents the largest series of patients with ALL treated uniformly for an isolated CNS relapse. Since marrow relapse remains the primary site of failure, future protocols must intensify systemic therapy.

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