Distinct nuclear and cytoplasmic functions of androgen receptor cofactor p44 and association with androgen-independent prostate cancer

Abstract

Androgen receptor (AR) mediates transcriptional activation of diverse target genes through interactions with various coactivators that may alter its function and help mediate the switch between prostate cell proliferation and differentiation. We recently identified p44/MEP50 as an AR coactivator and further showed that it is expressed primarily in the nucleus and cytoplasm of benign prostate epithelial and prostate cancer cells, respectively. We also showed that haploinsufficiency in p44 ؉/؊ mice causes prostate epithelial cell proliferation. To establish direct cause-andeffect relationships, we have used p44 fusion proteins that are selectively expressed in the nucleus or cytoplasm of prostate cancer cells (LNCaP), along with RNAi analyses, to examine effects of p44 both in vitro and in vivo (in tumor xenografts). We show that preferential expression of p44 in the nucleus inhibits proliferation of LNCaP cells in an AR-dependent manner, whereas preferential expression of p44 in the cytoplasm enhances cell proliferation. These effects appear to be mediated, at least in part, through the regulation of distinct cell-cycle regulatory genes that include p21 (up-regulated by nuclear p44) and cyclin D2 and CDK6 (up-regulated by cytoplasmic p44). Importantly, we also demonstrate that altered p44 expression is associated with androgen-independent prostate cancer. Our results indicate that nuclear p44 and cytoplasmic p44 have distinct and opposing functions in the regulation of prostate cancer cell proliferation. Mep50 ͉ prostate cancer growth H ormone refractory or androgen-independent prostate cancer remains the primary cause of cancer-related death. Androgens and androgen receptors (ARs) play crucial roles in prostate cancer oncogenesis and progression, including progression into androgenindependent cancer (1-3). AR, a member of the steroid hormone receptor family (4), is a transcription factor with an important role in the regulation of normal prostate growth and differentiation. On the one hand, AR can increase prostate cell proliferation; on the other hand, AR can also inhibit proliferation of prostate cells (5, 6). The mechanism underlying the AR-mediated switch between proliferation and growth suppression remains to be elucidated. In association with its coactivators, AR binds to androgen-responsive elements and activates transcription of AR target genes (4). AR coactivators affect the transcriptional activity of AR by altering its association with either the general transcriptional machinery (7) or chromatin-modifying complexes such as those with histone acetylation or methylation activity (8, 9).Increasing numbers of AR coactivators have been described recently. We and others have observed diverse expression patterns of some cofactors involved in human prostate cancer. Increased expression of some cofactors (ARA24, PIAS1, cyclinD1, SRC1, FHL2, and Par4) and decreased expression of others (ARA70 and ART-27) are found in prostate cancer tissue when compared with adjacent benign tissue (10-15). Thus alterations in ...

Neonatal Gonocyte Differentiation in Mongolian GerbilMeriones unguiculatusInvolves Asynchronous Maturation of Seminiferous Cords and Rapid Formation of Transitional Cell Stage

“…The molecular mechanisms underlying AR inactivation are complex and deserve further investigation in this species. In many cases, especially in prostate cells, the exportation of AR from the nucleus to the cytoplasm and their inactivation has been related to androgen withdrawal (Tyagi et al, 2000, Gregory et al, 2001, Peng et al, 2008. Given that previous gerbil hormonal data evidenced a decline in serum androgen levels only around 14 d (Siegford et al, 2003), it is probable that other cofactors might be involved in neonatal ARinactivation.…”

Repression of Androgen Receptor Activity by HEYL, a Third Member of the Hairy/Enhancer-of-split-related Family of Notch Effectors

“…In support of this, p44, an AR coregulator, is mislocalized to the cytoplasm in prostate cancer but not matched benign sections (45). Intriguingly, nuclear p44 appears to have an antiproliferative role, but cytoplasmic p44 has an opposing, proliferative role in prostate cell line growth (45,46). Further analysis of primary tumor biopsies, sequencing of HEY genes for mutations in regions important for nuclear localization, and analysis of potential sites of post-translational modification may increase our understanding of the mechanisms and significance of HEY protein exclusion in prostate cancer.…”

Molecular cloning, characterization and association analysis of the promoter region of the bovine CDK6 gene

“…CDK6 was shown to be required for proper thymocyte development and tumorigenesis (Hu et al, 2009). Most recently, NANOG in embryonic stem cells, MEP50 in prostate cancer cells and Smad in osteoblast were shown to directly regulate CDK6 transcription (Ogasawara et al, 2004a;Peng et al, 2008;Zhang et al, 2009). Additional evidence of CDK6 function in developmental processes showed that CDK6 expression was regulated by developmentally important miRNAs (Johnson et al, 2007;Lujambio et al, 2007;Silber et al, 2008).…”