The T cell antigen receptor activates phosphatidylinositol 3-kinase-regulated serine kinases protein kinase B and ribosomal S6 kinase 1.

The present study has explored T cell antigen receptor-regulated serine kinases in human T cells. The results identify two phosphatidylinositol 3-kinase (PI3K)-controlled serine kinases operating downstream of the T cell receptor (TCR) in primary T cells: (i) protein kinase B whose activation regulates the phosphorylation of glycogen synthase kinase 3 and (ii) ribosomal S6 kinase 1, a kinase with a critical role in the regulation of protein synthesis and cell growth. T cells express two isoforms of S6k1: a 70 kDa cytoplasmic kinase and an 85 kDa isoform that has a classic nuclear localisation. TCR ligation triggers a parallel engagement of both the 70 and 85 kDa isoforms of S6k1 in a response that requires PI3K function.