RPS6KA1 and sarcoma: Also, the rat sarcoma (RAS)/rapidly accelerated fibrosarcoma (Raf)/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK)/p90 ribosomal S6 kinase 1 (p90RSK1) cascade impinges on mTORC1, as both ERK and p90RSK1 phosphorylate TSC2 (at Ser664 and Ser1798, respectively), thereby inhibiting the TSC1/TSC2 complex and triggering Rheb-dependent mTORC1 activation [20].