- Insulin-dependent Stimulation of a Subtype of p38Map Kinases and Its Role in Insulin's Antiapoptotic Activity.
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Shin Hae Kang, Ji Hoon Kang, Hee Kyoung Kang, Dae Ho Lee, Young Ki Lee, Deok Bae Park
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J Korean Endocr Soc. 2004;19(4):358-368. Published online August 1, 2004
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 Abstract
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- BACKGROUND
The p38 mitogen-activated protein kinases (p38Map kinases) are a family of prolinedirected serine/threonine kinases. At least four isoforms of p38Map kinases have been identified; however, their physiological significances remain to be understood. Recently, the role of p38Map kinase in insulin-stimulated glucose uptake has been suggested. The present study aimed to investigate which isoform(s) were responsive to insulin stimulation. In addition, the activities of p38 Map kinase isoforms that may participate in the insulin's antiapoptotic function in CHO-IR cells were also determined. METHODS: Chinese hamster ovary cells, expressing wild- or mutated human insulin receptors (CHO-IR cells), were used to investigate whether insulin can stimulate any of the isoform(s) of the p38Map kinases. The p38Map kinase activity was determined by measuring the degree of 32P-labelling of ATF-2 protein, a specific substrate of p38Map kinase. A DNA laddering assay was performed to examine the degree of apoptosis and a RT-PCR analysis to determine which isoform(s) of the p38Map kinases were expressed in response to insulin. RESULTS: p38Map kinase activation by insulin was sharply suppressed in only the CHO-IR/A1018K cells, which lack the intrinsic tyrosine kinase activity of insulin receptors. Insulin stimulation of p38Map kinase was insensitive to SB203580, an inhibitor of the alpha(alpha)-and beta(beta)-isoforms of p38Map kinases. Moreover, orthovanadate, known as a specific stimulator of the gamma(gamma)-and delta(delta-) isoforms, stimulated the p38Map kinase activity in CHO-IR cells. Insulin increased the degree of mRNA expression of the delta-isoform, but not that of the alpha-isoform p38Map kinase. Interestingly, PD98059, an inhibitor of ERK, suppressed p38Map kinase stimulation, as well as the antiapoptotic protection of cells by insulin. As insulin was found to still protect ERK-lacking cells (CHO-IR/ SOS) from apoptosis, any substantial role(s) of ERK might be excluded. CONCLUSION: Our data suggest that insulin may stimulate the activity and expression of the-isoform of p38Map kinase in a MEK1/2-dependent manner. The involvement of the delta-isoform of p38Map kinase in insulin's antiapoptotic protection was also suggested, but remains to be investigated further to clarify the nature of its mechanism of action
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