Nuclear S6K1 regulates cAMP-responsive element-dependent gene transcription through activation of mTOR signal pathway

S6K1 serves as an important signaling regulator of cell proliferation and growth in the mTOR signaling pathway. Excessive activation of the mTOR/S6K1 signaling pathway promotes abnormal cell growth and survival, thereby resulting in tumorigenesis. The roles of S6K1 in protein synthesis and metabolism are well known, but an additional role of S6K1 as a gene transcription regulator has not been much understood. Here, we demonstrated that S6K1 is dynamically distributed in the cytoplasm and nuclei of human cervical cancer cells. S6K1 nuclear localization was serum dependent and serum deprivation or rapamycin treatment inhibited S6K1 Thr389 phosphorylation and, thereby, S6K1 was retained in the cytoplasm. Furthermore, we found that endogenous S6K1 interacted with CREB in the cervical cancer cells. Additionally, S6K1 upregulated the CRE-driven promoter luciferase activity. The proto-oncogene c-JUN, which has several CREs, was attenuated in the S6K1 knockdown cervical cancer cells. The binding of CREB/S6K1 to the c-JUN promoter, altered by serum restimulation, was associated with active epigenetic markers. In HeLa cell, 891 promoter regions, to which S6K1 directly binds, were detected. Our findings suggested that active S6K1, which is dynamically translocated into the nucleus, directly binds to chromatin and could play a role in epigenetic mechanisms or transcription factor recruitment.