The ribosomal S6 kinase p70(S6k) is involved in the regulation of the proliferation of hematopoietic cell lines but not in the induction of erythroid differentiation by erythropoietin

The ribosomal S6 kinase p70(S6k) is supposed to be involved in the translational control through the phosphorylation of the 40S ribosomal subunit protein S6. Here we show that the proliferative status of several cytokine-responsive hematopoietic cell lines correlates well with p70(S6k) activity. In contrast, erythropoietin-induced erythroid maturation of J2E cells proceeds independently of p70(S6k) function. In the erythropoietin-dependent cell line HCD-57, p70(S6k) appears to be regulated through different erythropoietin-induced pathways. Protein synthesis is supposed to be regulated in part by the multiple phosphorylation of the 40S ribosomal protein S6(1), which is mediated by the serine/threonine specific protein kinase p70(S6k). In-2 rat embryo fibroblasts, p70(S6k) function was shown to be essential throughout the G1 phase of the cell cycle. (3)Activation of the enzyme requires multiple independent inputs(4) and is associated with phosphorylation of several clustered serine/threonine residues in a putative autoinhibitory domain of the kinase. (5)P70(S6k) is regulated through common protein kinase C (cPKC)-dependent and independent pathways. In-6 Somecell types, the PI 3-kinase was shown to mediate activation of p70(S6k). (7,8)