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KMID : 0366919950070010001
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Sungkyun Pharmceutical Journal
1995 Volume.7 No. 1 p.1 ~ p.6
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p70^s6k/p85^s6k：Mechanism of Activation and Role in Mitogenesis
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Lee Hyang-Woo
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Abstract
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ABSTRACT: Activation of cell growth leads to the multiple phosphorylation of 40S ribosomal protein S6. The kinase responsible for controlling this event is termed p70^s6k/p85^s6k. Both isoforms of the kinase are derived from a common gene activated by a complex set of phosphorylation events; each residues in a unique cellular compartment: the p70^s6k in the cytoplasm and the p85^s6k in the nucleus. Although p70^s6k/p85^s6k represent the first mitogen-activated serine/threonine kinase described, the signaling pathway leading to activation of both isoforms remains obscure. Recent studies have shown that this pathway is distinct from that of p21^ras and the p42^mapk/p44^mapk, and that bifurcation of these pathways takes place at the level of the receptor. The p70^s6k signaling pathway can also be ablated by the immunosuppressant rapamycin, which blocks p70^s6k activation and S6 phosphorylation without affecting the other kinases whose activation is triggered by mitogen treatment. In parallel, rapamycin suppresses the translation of a family of mRNAs that contain a polypyrimidine tract at their 5´ transcriptional start site. The implication is that this event is mediated by the phosphorylation form of S6 that may either directly interact with the polypyrimidine tract or alter the affinity of the 40S ribosome mRNA binding site for polypyrimidine tract mRNAs, or recognize proteins that directly bind to the polypyrimidine tract.
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