Protein kinase C delta (PKC delta) 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 PKC delta activity and increases PKC delta protein and RNA levels, and that the SP-1 transcription factor is involved in insulin-induced transcription of the PKC delta gene. Activation of SP-1 involves serine phosphorylation and translocation to the nucleus. In this study we examined the possibility that PKC alpha 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 PKC alpha, and insulin stimulation caused these proteins to dissociate. In contrast, in the nucleus insulin induced an increase in association between PKC alpha and SP-1. PKC alpha inhibition blocked insulin-induced serine phosphorylation of SP-1 and its association with PKC alpha in the nucleus. Inhibition of PKC alpha also reduced the insulin-induced increase in PKC delta RNA and protein in the cytoplasmic and nuclear fractions. We also attempted to determine if another transcription factor might be involved in regulation of PKC delta expression. We earlier showed that insulin did not affect nuclear NF kappa B levels. Inhibition of NF kappa B, however, increased insulin-induced increase in PKC delta RNA and protein in the cytoplasmic and nuclear fractions. Surprisingly, this inhibition reduced the insulin-induced increase in cytoplasmic and nuclear PKCa RNA and protein. Inhibition of PKC delta reduced I kappa B alpha phosphorylation as well as NF kappa B activation. Thus, PKC alpha regulates insulin-induced PKC delta expression levels and this regulation involves activation of SP-1 and NF kappa B. (c) 2006 Elsevier Inc. All rights reserved.