Different interactomes for p70-S6K1 and p54-S6K2 revealed by proteomic analysis.

S6Ks are major effectors of the mTOR (mammalian target of rapamycin) pathway, signaling for increased protein synthesis and cell growth in response to insulin, AMP/ATP levels, and amino acids. Deregulation of this pathway has been related to disorders and diseases associated with metabolism, such as obesity, diabetes, and cancer. S6K family is composed of two main members, S6K1 and S6K2, which comprise different isoforms resulted from alternative splicing or alternative start codon use. Although important molecular functions have been associated with p70-S6K1, the most extensively studied isoform, the S6K2 counterpart lacks information. In the present study, we performed immunoprecipitation assays followed by mass spectrometry (MS) analysis of FLAG-tagged p70-S6K1 and p54-S6K2 interactomes, after expression in HEK293 cells. Protein lists were submitted to CRAPome (Contaminant Repository for Affinity Purification) and SAINT (Significance Analysis of INTeractome) analysis, which allowed the identification of high-scoring interactions. By a comparative approach, p70-S6K1 interacting proteins were predominantly related to "cytoskeleton" and "stress response," whereas p54-S6K2 interactome was more associated to "transcription," "splicing," and "ribosome biogenesis." Moreover, we have found evidences for new targets or regulators of the S6K protein family, such as proteins NCL, NPM1, eIF2α, XRCC6, PARP1, and ILF2/ILF3 complex. This study provides new information about the interacting networks of S6Ks, which may contribute for future approaches to a better understanding of the mTOR/S6K pathway.

S6Ks isoforms contribute to viability, migration, docetaxel resistance and tumor formation of prostate cancer cells.

BACKGROUND: The S6 Kinase (S6K) proteins are some of the main downstream effectors of the mammalian Target Of Rapamycin (mTOR) and act as key regulators of protein synthesis and cell growth. S6K is overexpressed in a variety of human tumors and is correlated to poor prognosis in prostate cancer. Due to the current urgency to identify factors involved in prostate cancer progression, we aimed to reveal the cellular functions of three S6K isoforms-p70-S6K1, p85-S6K1 and p54-S6K2-in prostate cancer, as well as their potential as therapeutic targets. METHODS: In this study we performed S6K knockdown and overexpression and investigated its role in prostate cancer cell proliferation, colony formation, viability, migration and resistance to docetaxel treatment. In addition, we measured tumor growth in Nude mice injected with PC3 cells overexpressing S6K isoforms and tested the efficacy of a new available S6K1 inhibitor in vitro. RESULTS: S6Ks overexpression enhanced PC3-luc cell line viability, migration, resistance to docetaxel and tumor formation in Nude mice. Only S6K2 knockdown rendered prostate cancer cells more sensitive to docetaxel. S6K1 inhibitor PF-4708671 was particularly effective for reducing migration and proliferation of PC3 cell line. CONCLUSIONS: These findings demonstrate that S6Ks play an important role in prostate cancer progression, enhancing cell viability, migration and chemotherapy resistance, and place both S6K1 and S6K2 as a potential targets in advanced prostate cancer. We also provide evidence that S6K1 inhibitor PF-4708671 may be considered as a potential drug for prostate cancer treatment.