Involvement of PKCalpha in insulin-induced PKCdelta expression: Importance of SP-1 and NFkappaB transcription factors.
Protein kinase C delta (PKCdelta) is a key molecule in insulin signaling essential for insulin-induced glucose transport in skeletal muscle. Recent studies in our laboratory have shown that insulin rapidly stimulates PKCdelta activity and increases PKCdelta protein and RNA levels, and that the SP-1 transcription factor is involved in insulin-induced transcription of the PKCdelta gene. Activation of SP-1 involves serine phosphorylation and translocation to the nucleus. In this study we examined the possibility that PKCalpha might be involved in serine phosphorylation and activation of SP-1. We found that insulin rapidly phosphorylates and translocates SP-1. In the cytoplasm, SP-1 was constitutively associated with PKCalpha, and insulin stimulation caused these proteins to dissociate. In contrast, in the nucleus insulin induced an increase in association between PKCalpha and SP-1. PKCalpha inhibition blocked insulin-induced serine phosphorylation of SP-1 and its association with PKCalpha in the nucleus. Inhibition of PKCalpha also reduced the insulin-induced increase in PKCdelta RNA and protein in the cytoplasmic and nuclear fractions. We also attempted to determine if another transcription factor might be involved in regulation of PKCdelta expression. We earlier showed that insulin did not affect nuclear NFkappaB levels. Inhibition of NFkappaB, however, increased insulin-induced increase in PKCdelta RNA and protein in the cytoplasmic and nuclear fractions. Surprisingly, this inhibition reduced the insulin-induced increase in cytoplasmic and nuclear PKCalpha RNA and protein. Inhibition of PKCdelta reduced IkappaBalpha phosphorylation as well as NFkappaB activation. Thus, PKCalpha regulates insulin-induced PKCdelta expression levels and this regulation involves activation of SP-1 and NFkappaB.
Horovitz-Fried
Miriam
M
The Faculty of Life Sciences, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel.
Sampson
Sanford R
SR
D000818:Animals; D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011485:Protein Binding; D051571:Protein Kinase C-alpha / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics*
D007328:Insulin; D016328:NF-kappa B; D016329:Sp1 Transcription Factor; D010768:Phosphoserine; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta