Estrogen receptor α(ERα) target gene LRP16 interacts with ERα and enhances receptor's transcriptional activity

Objective: It has been shown that LRP16 is an estrogen-induced gene through its receptor alpha(ER alpha). Although there is evidence demonstrating that inhibition of LRP16 gene expression in MCF-7 human breast cancer cells partially attenuates its estrogen-responsiveness, the underlying molecular mechanism is still unclear. Here, the effect of LRP16 expression on the ER alpha signaling transduction was investigated. Methods: Cotransfection assays were used to measure the effect of LRP16 on ER alpha-mediated transcriptional activity. GST-pulldown and immunoprecipitation ( CoIP) assays were employed to investigate the physical interaction of LRP16 and ER alpha. The mammalian two-hybrid method was used to map the functional interaction region. Results: the results of cotransfection assays demonstrated that the transcriptional activities of ER alpha were enhanced in a LRP16 dose-dependent manner in MCF-7 in the presence of estrogen, however, it was abolished in the absence of E2 in MCF-7 cells. The physical interaction of LRP16 and ER alpha proteins was confirmed by GST-pulldown in vitro and CoIP in vivo assays, which was enhanced by E2 but not dependent on its presence. Furthermore, the results of the mammalian two-hybrid assays indicated that the binding region of ER alpha to LRP16 located at the A/B AF-1 functional domain and E2 stimulated the binding of LRP16 to the full-length ER alpha molecule but not to the A/B region alone. Conclusion: These results support a role for estrogenically regulated LRP16 as an ER alpha coactivator, providing a positive feedback regulatory loop for ER alpha signal transduction. Based on this function of LRP16, we propose that ER alpha-positive breast cancer patients with high expression of LRP16 might benefit from targeting LRP16 therapy.