Ribosomal protein S6 kinase beta-1 and Eukaryotic translation initiation factor 4E-binding protein 1 (S6K1 and 4E-BP1)

Ribosomal protein S6 kinase beta-1 (S6K1) and Eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) are the two primary downstream effectors of the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway [1, 6]. They serve as critical regulators of protein synthesis and cell growth by integrating signals from nutrients, growth factors, and cellular energy levels [1, 14]. mTORC1 activates S6K1 through phosphorylation at Thr389, which in turn phosphorylates ribosomal protein S6 and other substrates to enhance the translation of specific mRNA subsets [1, 9]. Simultaneously, mTORC1 phosphorylates 4E-BP1 at multiple sites, causing it to dissociate from the translation initiation factor eIF4E and thereby permitting the assembly of the eIF4F complex for cap-dependent translation [1, 10]. Dysregulation of the S6K1 and 4E-BP1 axes is a hallmark of many cancers, driving uncontrolled cell proliferation and survival, and is also implicated in metabolic disorders such as obesity and type 2 diabetes [2, 14]. These proteins are widely used as pharmacodynamic biomarkers to assess the efficacy of mTOR inhibitors, including rapamycin and its analogs, as well as next-generation ATP-competitive mTOR kinase inhibitors [5, 8]. While rapamycin primarily inhibits S6K1, newer ATP-competitive inhibitors more effectively suppress 4E-BP1 phosphorylation, which is often associated with drug resistance in cancer [5, 8]. Therapeutic strategies targeting these effectors aim to restore normal translational control in diseases characterized by hyperactive mTOR signaling [3, 7]. In addition to cancer, these pathways are being explored for their roles in neuroprotection and axon regeneration following central nervous system injury [1, 12].

Other names

p70S6KRPS6KB1STK14Ap70 S6 kinaseEIF4EBP1PHAS-I4EBP1p70-S6K1

mTORC1 inhibition, S6K1 inhibition, 4E-BP1 activation (via dephosphorylation)