Phospho-p70 S6 kinase (Thr389) Recombinant Rabbit mAb

Phospho-p70 S6 kinase (Thr389) refers to the phosphorylated form of the 70 kDa ribosomal protein S6 kinase at threonine 389, a key modification that serves as the principal indicator of p70S6K kinase activity in vivo and a widely used readout for mTORC1 pathway activation. Thr389 lies within the linker domain of p70S6K, and its phosphorylation is stimulated by growth factors such as insulin, EGF, and serum, as well as by mechanical stimuli, while being blocked by PI3K inhibitors (wortmannin, LY294002) and the mTOR inhibitor rapamycin. mTOR is the rapamycin-sensitive kinase that directly confers Thr389 phosphorylation, and prior phosphorylation of Thr389 is required for PDK1 to subsequently act on Thr229 in the activation loop, making Thr389 a prerequisite for full kinase activation. Beyond its role in kinase activation, Thr389 phosphorylation is also essential for the nuclear localization of p70S6K, with only hyperphosphorylated p70S6K detectable in the nucleus. In experimental research, site-specific antibodies against phospho-p70S6K (Thr389) are widely used in Western blotting and immunocytochemistry to monitor mTORC1 activity, and commercial antibodies detect the ~70 kDa p70 isoform as well as the ~85 kDa p85 isoform when phosphorylated at the analogous site.