LRP16 is a special member of the macro domain superfamily, containing only a stand-alone macro domain functional module. Previous study demonstrated that the estrogenically regulated LRP16 cooperates with the estrogen receptor α and enhances the receptor's transcriptional activity in an estrogen-dependent manner. Here, we discovered that LRP16 binds to androgen receptor (AR) via its macro domain and amplifies the transactivation function of AR in response to androgen. Similarly, we also discovered that LRP16 acts as a potential coactivator to amplify the transactivation of at least other four nuclear receptors (NRs). Importantly, we show that the single macro domain in LRP16 can serve as the AR coactivator. RNA interference knockdown of LRP16 leads to impaired AR function and greatly attenuates the coactivation of AR by other AR coactivators such as ART-27 and steroid receptor coactivator-1. This interference also markedly inhibits the androgen-stimulated proliferation of androgen-sensitive LNCaP prostate cancer cells. However, LRP16 knockdown did not significantly affect the growth rate of AR-negative PC-3 prostate cancer cells. Furthermore, we observed the induction effect of LRP16 expression by androgen and established a feedforward mechanism that activated AR transactivation. Our results suggest that the macro domain protein LRP16 represents a novel type of cofactor of NR. They also indicate that LRP16 plays an essential role in AR transactivation.
J Yang, Y-L Zhao, Z-Q Wu, Y-L Si, Y-G Meng, X-B Fu, Y-M Mu and W-D Han
W-D Han, Y-L Zhao, Y-G Meng, L Zang, Z-Q Wu, Q Li, Y-L Si, K Huang, J-M Ba, H Morinaga, M Nomura and Y-M Mu
Previous studies have shown that leukemia related protein 16 (LRP16) is estrogenically regulated and that it can stimulate the proliferation of MCF-7 breast cancer cells, but there are no data on the mechanism of this pathway. Here, we demonstrate that the LRP16 expression is estrogen dependent in several epithelium-derived tumor cells. In addition, the suppression of the endogenous LRP16 in estrogen receptor α (ERα)-positive MCF-7 cells not only inhibits cells growth, but also significantly attenuates the cell line’s estrogen-responsive proliferation ability. However, ectopic expression of LRP16 in ERα-negative MDA-MB-231 cells has no effect on proliferation. These data suggest the involvement of LRP16 in estrogen signaling. We also provide novel evidence by both ectopic expression and small interfering RNA knockdown approaches that LRP16 enhances ERα-mediated transcription activity. In stably LRP16-inhibitory MCF-7 cells, the estrogen-induced upregulation of several well-known ERα target genes including cyclin D1 and c-myc is obviously impaired. Results from glutathione S-transferase pull-down and coimmunoprecipitation assays revealed that LRP16 physically interacts with ERα in a manner that is estrogen independent but is enhanced by estrogen. Furthermore, a mammalian two-hybrid assay indicated that the binding region of LRP16 localizes to the A/B activation function 1 domain of ERα. Taken together, these results present new data supporting a role for estrogenically regulated LRP16 as an ERα coactivator, providing a positive feedback regulatory loop for ERα signal transduction.
Yang-Hsiang Lin, Meng-Han Wu, Ya-Hui Huang, Chau-Ting Yeh, Hsiang-Cheng Chi, Chung-Ying Tsai, Wen-Yu Chuang, Chia-Jung Yu, I-Hsiao Chung, Ching-Ying Chen and Kwang-Huei Lin
Thyroid hormone (T3) and its receptor (TR) are involved in cancer progression. While deregulation of long non-coding RNA (lncRNA) expression has been detected in many tumor types, the mechanisms underlying specific involvement of lncRNAs in tumorigenicity remain unclear. Experiments from the current study revealed negative regulation of BC200 expression by T3/TR. BC200 was highly expressed in hepatocellular carcinoma (HCC) and effective as an independent prognostic marker. BC200 promoted cell growth and tumor sphere formation, which was mediated via regulation of cell cycle-related genes and stemness markers. Moreover, BC200 protected cyclin E2 mRNA from degradation. Cell growth ability was repressed by T3, but partially enhanced upon BC200 overexpression. Mechanistically, BC200 directly interacted with cyclin E2 and promoted CDK2–cyclin E2 complex formation. Upregulation of cell cycle-related genes in hepatoma samples was positively correlated with BC200 expression. Our collective findings support the utility of a potential therapeutic strategy involving targeting of BC200 for the treatment of HCC.