Cloning and characterization of p70(S6K beta) defines a novel family of p70 S6 kinases.

The human cDNA encoding a novel protein serine/threonine kinase most closely related to p70 S6 kinase was isolated from the human erythroleukemia cDNA library and termed p70(S6Kbeta). p70(S6Kbeta) has 67% amino acid identity in overall sequence with human p70(S6K), and the potential phosphorylation sites of p70(S6K) are conserved in p70(S6Kbeta). Northern blot analysis identified two major transcripts of p70(S6Kbeta) that are ubiquitously expressed in human adult tissues. Similar to p70(S6K), p70(S6Kbeta) was activated by serum stimulation, and the serum-induced activation was inhibited by wortmannin and rapamycin. These findings suggest that p70(S6Kbeta) is an isoform of p70(S6K) with similar regulatory mechanisms.