Background: Androgen receptor (AR) signaling pathways play pivotal roles in the onset and progression of prostate cancer. Despite the fact that androgen-ablation therapy initially triggers tumor regression, virtually all invasive and metastatic prostate cancers eventually progress into a fatal androgen-independent disease. Paradoxically, most of these androgen-independent tumors continue to express AR and remain dependent on AR signaling pathways for growth and proliferation. Unfortunately, the molecular mechanisms underlying this pathology remain poorly understood. Recent studies suggest that hyperactivation or amplification of key AR coregulatory factors may promote tumor progression to the androgen-independent stage. We have found that the MED1 subunit of the Mediator transcriptional coactivator complex is essential for robust AR-dependent transcription and for prostate cancer cell proliferation. Moreover, we have discovered that MED1 expression is amplified in a number of human and mouse prostate cancer specimens and cell lines.Hypothesis: We hypothesize that MED1 regulates AR activity in prostate cancer cells and that its amplification or de-regulated expression may be an important oncogenic event that promotes prostate cancer progression towards the androgen-independent stage of the malignancy.Specific Aims and Study Design:Aim 1: Precisely map the interaction domains of MED1 and AR. We will carry out in vivo and in vitro binding assays using MED1 and AR deletion and point mutants in the presence and absence of androgens. These studies will also address whether ERK phosphorylation of MED1 influences its interaction with AR.Aim 2: Determine MED1 expression levels in the prostate epithelium as a function of prostate cancer progression and age. We will perform MED1 immunohistochemical (IHC) analyses on human tissue microarrays containing statistically significant numbers of prostate cancers of varying Gleason grades, hormone-refractory tumors, and metastases. We will also determine MED1 levels in the progressive stages of a mouse model of prostate cancer and in normal mouse prostates of different ages (0 to 39 months). In each study, we will further examine whether there is a correlative pattern between activated ERK levels and MED1 levels.Aim 3: Investigate the functional consequences of MED1 amplification or silencing in an animal xenograft model of prostate cancer progression. We will ectopically overexpress or silence MED1 expression in LNCaP and LAPC-4 cells via recombinant lentivirus. The cells will then be injected into male nude mice and tumor growth will be measured. Mice will also be castrated to further address whether MED1 amplification promotes or accelerates androgen-independent tumor growth. IHC analyses will also be performed to confirm MED1 overexpression or silencing, and to assess markers of tumor progression.Innovation and Impact: While it is clearly established that MED1 is an essential coactivator for steroid hormone receptors, its pathological role and expression during prostate cancer progression remains largely undefined. This study is innovative in that it will provide fresh insights into MED1's coregulatory role during prostate cancer initiation and progression to the terminal androgen-independent disease. Indeed, we anticipate that an important outcome from our work may be that elevated MED1 expression is a molecular marker for specific stages of prostate cancer progression, and furthermore, establish whether such expression is predominant in specific types of cells within the prostate epithelium. It is also envisaged that the experiments here may lead to the development of small molecules that either block MED1-AR interactions or inhibit MED1 function. Significantly, and relevant to clinical progression of prostate cancer, a future direction of this work may be the identification of pathologically associated MED1 mutant alleles that confer aberrant (e.g., androgen-independent) MED1-AR interactions. Moreover, the studies here may lead to the discovery of novel or alternative targets (e.g., other Mediator complex subunits or associated enzymes) for therapeutic intervention.Focus Areas: The studies proposed here are expected to impact at least four out of the five Fiscal Year 2009 PCRP focus areas: (1) Biomarkers: The work in Aim 2 could directly lead to the discovery of novel biomarkers prognostic for distinct stages of prostate cancer progression (e.g., late-stage hormone-refractory disease) or possibly have implications for alternative therapeutic treatments. (2) Therapy: The work in Aim 1 may lead to the development of small chemical compounds that act therapeutically by blocking MED1-AR interactions. (3) Genetics: As an extension of the work in Aim 1 (that will precisely define the MED1-AR interaction motifs), our data may help identify pathologically-linked MED1 alleles that confer aberrant interactions with AR and consequently influence AR activity. (4) Tumor Biology: Significantly, the studies here will help clarify the molecular roles of MED1 and AR during prostate cancer initiation and progression to the terminal androgen-independent disease.
|Effective start/end date||6/15/10 → 6/14/15|
- Congressionally Directed Medical Research Programs (CDMRP)
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