Androgen receptor coactivator ARA70alpha and ARA70beta isoform-specific antibodies: new tools for studies of expression and immunohistochemical localization

Androgen receptor cofactors: A potential role in understanding prostate cancer

Prostate cancer (PCa) is witnessing a concerning rise in incidence annually, with the androgen receptor (AR) emerging as a pivotal contributor to its growth and progression. Mounting evidence underscores the AR's ability to recruit cofactors, influencing downstream gene transcription and thereby fueling the proliferation and metastasis of PCa cells. Although, clinical strategies involving AR antagonists provide some relief, managing castration resistant prostate cancer (CRPC) remains a formidable challenge. Thus, the need of the hour lies in unearthing new drugs or therapeutic targets to effectively combat PCa. This review encapsulates the pivotal roles played by coactivators and corepressors of AR, notably androgen receptor-associated protein (ARA) and steroid receptor Coactivators (SRC) in PCa. Our data unveils how these cofactors intricately modulate histone modifications, cell cycling, SUMOylation, and apoptosis through their interactions with AR. Among the array of cofactors scrutinised, such as ARA70β, ARA24, ARA160, ARA55, ARA54, PIAS1, PIAS3, SRC1, SRC2, SRC3, PCAF, p300/CBP, MED1, and CARM1, several exhibit upregulation in PCa. Conversely, other cofactors like ARA70α, PIASy, and NCoR/SMRT demonstrate downregulation. This duality underscores the complexity of AR cofactor dynamics in PCa. Based on our findings, we propose that manipulating cofactor regulation to modulate AR function holds promise as a novel therapeutic avenue against advanced PCa. This paradigm shift offers renewed hope in the quest for effective treatments in the face of CRPC's formidable challenges.

Expression and function of nuclear receptor coactivator 4 isoforms in transformed endometriotic and malignant ovarian cells

Iron is proposed to contribute to the transition from endometriosis to specific subtypes of ovarian cancers (OVCAs). Regulation of intracellular iron occurs via a ferritinophagic process involving NCOA4 (Nuclear Receptor Coactivator 4), represented by two major isoforms (NCOA4α and NCOA4β), whose contribution to ovarian cancer biology remains uninvestigated. We thus generated transformed endometriotic cells (via HRAS^V12A, c-MYC^T58A, and p53 inactivation) whose migratory potential was increased in response to conditioned media from senescent endometriotic cells. We identified elevated NCOA4 mRNA in transformed endometriotic cells (relative to non-transformed). Knockdown of NCOA4 increased ferritin heavy chain (FTH1) and p21 protein which was accompanied by reduced cell survival while NCOA4β overexpression reduced colony formation. NCOA4α and NCOA4β mRNA were elevated in malignant versus non-malignant gynecological cells; NCOA4α protein was increased in the assessed malignant cell lines as well as in a series of OVCA subtypes (relative to normal adjacent tissues). Further, NCOA4 protein expression was regulated in a proteasome- and autophagy-independent manner. Collectively, our results implicate NCOA4 in ovarian cancer biology in which it could be involved in the transition from precursors to OVCA.

Mifepristone inhibits GRβ coupled prostate cancer cell proliferation

PURPOSE

The GR gene produces GRα and GRβ isoforms by alternative splicing of a C-terminal exon. GRα binds glucocorticoids, modulates transcription in a glucocorticoid dependent manner and has a growth inhibitory role in prostate cells. Due to this role glucocorticoids are often used to treat androgen independent prostate cancer. In contrast, GRβ has intrinsic transcriptional activity and binds mifepristone (RU486) but not glucocorticoids to control gene expression. To our knowledge the role of GRβ in prostate cell proliferation is unknown.

MATERIALS AND METHODS

We determined GRβ levels in various prostate cancer cell lines by reverse transcriptase-polymerase chain reaction and Western blot. The effect of GRβ on the kinetics of prostate cancer cell growth was determined by cell counting and flow cytometry upon mifepristone and dexamethasone treatment. Cell proliferation was also examined after siRNA mediated knockdown and over expression of GRβ.

RESULTS

GRβ mRNA and protein were up-regulated in LNCaP cells that over expressed the androgen receptor co-factor ARA70β. Treatment of LNCaP-ARA70β with mifepristone or siRNA targeting GRβ inhibited proliferation compared to that of parental LNCaP cells. The immortal but nontumorigenic RC165 prostate cell line and the tumorigenic DU145 prostate cell line with endogenous GRβ also showed partial growth reduction upon GRβ depletion but to a lesser extent than LNCaP-ARA70β cells. The growth stimulatory effect of ARA70β on LNCaP cells was partly GRβ dependent, as was the proliferation of RC165 cells and to a lesser extent of DU145 cells.

CONCLUSIONS

Results suggest that patients with a primary tumor that expresses GRβ and ARA70β may benefit from mifepristone.

Expression and function of nuclear receptor co-activator 4: evidence of a potential role independent of co-activator activity

Nuclear receptor coactivator 4 (NcoA4), also known as androgen receptor-associated protein 70 (ARA70), was initially discovered as a component of Ret-Fused Gene expressed in a subset of papillary thyroid carcinomas. Subsequent studies have established NcoA4 as a coactivator for a variety of nuclear receptors, including peroxisome proliferator activated receptors α and γ, and receptors for steroid hormones, vitamins D and A, thyroid hormone, and aryl hydrocarbons. While human NcoA4 has both LXXLL and FXXLF motifs that mediate p160 coactivator nuclear receptor interactions, this ubiquitously expressed protein lacks clearly defined functional domains. Several studies indicate that NcoA4 localizes predominantly to the cytoplasm and affects ligand-binding specificity of the androgen receptor, which has important implications for androgen-independent prostate cancer. Two NcoA4 variants, which may exert differential activities, have been identified in humans. Recent studies suggest that NcoA4 may play a role in development, carcinogenesis, inflammation, erythrogenesis, and cell cycle progression that may be independent of its role as a receptor coactivator. This review summarizes what is currently known of the structure, expression, regulation, and potential functions of this unique protein in cancerous and non-cancerous pathologies.

Dynamic distribution of nuclear coactivator 4 during mitosis: association with mitotic apparatus and midbodies

The cytoplasmic localization of Nuclear Receptor Coactivator 4 (NcoA4), also referred to as androgen receptor associated protein 70 (ARA70), indicates it may possess activities in addition to its role within the nucleus as a transcriptional enhancer. Towards identifying novel functions of NcoA4, we performed an in silico analysis of its amino acid sequence to identify potential functional domains and related proteins, and examined its subcellular distribution throughout the cell cycle. NcoA4 has no known or predicted functional or structural domains with the exception of an LxxLL and FxxLF nuclear receptor interaction motif and an N-terminal putative coiled-coil domain. Phylogenetic analysis indicated that NcoA4 has no paralogs and that a region referred to as ARA70-I family domain, located within the N-terminus and overlapping with the coiled-coil domain, is evolutionarily conserved in metazoans ranging from cnidarians to mammals. An adjacent conserved region, designated ARA70-II family domain, with no significant sequence similarity to the ARA70-I domain, is restricted to vertebrates. We demonstrate NcoA4 co-localizes with microtubules and microtubule organizing centers during prophase. Strong NcoA4 accumulation at the centrosomes was detected during interphase and telophase, with decreased levels at metaphase and anaphase. NcoA4 co-localized with tubulin and acetylated tubulin to the mitotic spindles during metaphase and anaphase, and to midbodies during telophase. Consistent with these observations, we demonstrated an interaction between NcoA4 and α-tubulin. Co-localization was not observed with microfilaments. These findings indicate a dynamic distribution of NcoA4 with components of the mitotic apparatus that is consistent with a potential non-transcriptional regulatory function(s) during cell division, which may be evolutionarily conserved.

Distinct function of androgen receptor coactivator ARA70α and ARA70β in mammary gland development, and in breast cancer

Steroid receptor coactivators are important in regulating the function of the receptors in endocrine organ development and in cancers, including breast. Androgen receptor (AR) coactivator ARA70, was first identified as a gene fused to the ret oncogene and later characterized as an AR coactivator. We previously reported that the full length ARA70α functions as a tumor suppressor gene and that ARA70β functions as an oncogene in prostate cancer. Here we show that both ARA70α and ARA70β function as AR and estrogen receptor (ER) coactivators in breast cancer cells. However, ARA70α and ARA70β serve different functions in mammary gland development and breast cancer tumorigenesis. We observed hypoplastic development of mammary glands in MMTV driven ARA70α transgenic mice and overgrowth of mammary glands in ARA70β transgenic mice at virgin and pregnant stages. We determined that ARA70α inhibited cell proliferation, and that ARA70β promotes proliferation in MCF7 breast cancer cells. These effects were observed in hormone-free media, or in media with androgen or estrogen, though to varying degrees. Additionally, we observed that ARA70β strongly enhanced the invasive ability of MCF7 breast cancer cells in in vitro Matrigel assays. Significantly, decreased ARA70α expression is associated with increased tendency of breast cancer metastasis. In summary, ARA70α and ARA70β have distinct effects in mammary gland development and in the progression of breast cancer.

Stimulation of prostate cancer cellular proliferation and invasion by the androgen receptor co-activator ARA70

ARA70 was first identified as a gene fused to the ret oncogene in thyroid carcinoma and subsequently as a co-activator for androgen receptor (AR). Two isoforms of ARA70 have been identified: a 70-kDa version called ARA70 alpha and an internally spliced 35-kDa variant termed ARA70 beta. We have previously reported that ARA70 alpha expression is reduced in prostate cancer, and its overexpression inhibits proliferation of LNCaP prostate cancer cells. However, the function of the ARA70 beta isoform in prostate cancer is not understood. In this report we examined the effects of ARA70 beta on AR transcriptional regulation as well as prostate cancer cellular proliferation and invasion. Although both ARA70 alpha and ARA70 beta functioned as transcriptional co-activators of AR in cell-based reporter assays, ARA70 beta overexpression, in contrast to ARA70 alpha, promoted prostate cancer cellular proliferation and invasion through Matrigel. Interestingly, genome-wide expression profiling of cells expressing ARA70 beta revealed an increase in the expression of genes involved in the control of cell division and adhesion, compatible with a role for ARA70 beta in proliferation and invasion. Consistent with its function in promoting cell growth and invasion, ARA70 beta expression was increased in prostate cancer. Our findings implicate ARA70 beta as a regulator of tumor cell growth and metastasis by affecting gene expression.