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

Abstract

The Hairy/Enhancer-of-split-related with YRPW-like motif (HEY) family of proteins are transcriptional repressors and downstream effectors of Notch signaling. We previously reported that HEY1 and HEY2 selectively repress androgen receptor (AR) signaling in mammalian cell lines and have shown that in human tissue HEY1 is excluded from the nuclei in prostate cancer but not benign prostatic hyperplasia. We have now characterized a third member of this family, HEYL, which is a more potent repressor of AR activity. HEYL interacted with and repressed AR activation function-1 domain and competitively inhibited SRC1e activation of AR transcriptional activity. Using a cell line inducibly expressing exogenous HEYL, we showed that HEYL represses endogenous AR-regulated genes and reduces androgen-dependent prostate cancer cell growth. Using a transrepression assay, we identified both trichostatin-sensitive and -insensitive domains within HEYL; however, analysis of endogenous AR target genes suggested that HEYL represses AR activity through histone deacetylase I/II-independent mechanisms. Immunohistochemical analyses of tissue indicated that, in a fashion similar to that previously reported for HEY1, HEYL is excluded from the nuclei in prostate cancer but not adjacent benign tissue. This suggests that nuclear exclusion of HEY proteins may be an important step in the progression of prostate cancer.

Notch signaling in the prostate: critical roles during development and in the hallmarks of prostate cancer biology

“…Therefore, these studies suggested that Notch and AR signaling suppressed each other in prostate cells. However, Belandia et al and Lavery et al also discovered that the interaction between Notch and AR signaling could be disrupted in prostate cancers whereby both Hey1 and HEYL were found to be excluded from the nucleus by unknown mechanisms (Belandia et al 2005;Lavery et al 2011). This disruption was correlated with the malignancy of prostate cancer.…”

“…In addition, HEYL, the third member of Hey family and also an effector of Notch signaling, was found to be a more potent repressor of AR signaling. Similar to Hey1, HEYL bound to AR activation function-1 and blocked AR activity, leading to the suppression of androgen-dependent prostate cancer cell growth (Lavery et al 2011). In contrast, a study also suggested that AR signaling repressed Notch signaling (Nantermet et al 2004).…”

“…Like normal prostate tissue, prostate cancer is also dependent on androgen for its growth. AR is expressed in cancer cells, and corruption of its downstream growth control mechanism, such as p53, plays a significant role in tumorigenesis and metastasis of prostate cancer (Chang et al 2014;Lavery et al 2011;Nantermet et al 2004). Therefore, inhibiting the activities of AR is a crucial step in treating primary prostate cancer to prevent tumor progression (Karantanos et al 2013).…”

Bringing androgens up a NOTCH in breast cancer

“…5. Studies on prostate tissue and cancer cell lines elucidated a role for the downstream NOTCH transcriptional repressors, HEY1 and HEYL, in the inhibition of AR-mediated gene transcription via interactions with the AF1 region of AR and direct competition with the AR coactivator SRC1 (Belandia et al 2005, Belandia & Parker 2006, Lavery et al 2011. This was proposed as a mechanism by which aberrant prostate growth develops androgen independence.…”

Hey Factors at the Crossroad of Tumorigenesis and Clinical Therapeutic Modulation of Hey for Anticancer Treatment

“…Heterodimers between Hes1 and Hey factors potentially silence achaete-scute homolog 1, which results in the maintenance of an undifferentiated state of tumors (124)(125)(126). Histone deacetylases (HDAC) are potentially involved in the repressive effects of Hey factors, as treatment with trichostatin A, a pan class I and II HDAC inhibitor, partially abrogates the repressive effect of Hey factors (127)(128)(129). It has been suggested that Hey factors can use their bHLH domain to recruit the mSin3-NCoR-HDAC1 complex or associate with SIRT1, a member of NAD þ -dependent HDACs, and induce transcriptional repression (11,127).…”