Protein kinase C isoform expression during the differentiation of 3T3-L1 preadipocytes: Loss of protein kinase C-α isoform correlates with loss of phorbol 12-myristate 13-acetate activation of nuclear factor κB and acquisition of the adipocyte phenotype

Abstract

The regulated expression of protein kinase C (PKC) isoforms was examined during the differentiation program of 3T3-L1 preadipocytes. In a parallel analysis, differentiation was blocked by treatment of the cells with tumor necrosis factor-alpha (TNF) to determine differentiation-specific changes in isoform expression from growth or treatment-induced effects. This analysis revealed that the expression of the conventional PKC-alpha isoform was reduced by 85% as cells attained the adipocyte phenotype. PKC-beta expression was measurable only during the early stages of the differentiation process and was not detectable in fully differentiated cells. An upregulation of PKC-theta, a novel PKC isoform, occurred during the latter stage of differentiation. Expression of PKC-zeta an atypical PKC isoform suggested to participate in TNF signal transduction, occurred throughout the time course with similar levels of expression in both preadipocytes and adipocytes. Nuclear run-on analysis demonstrated an approximately 85% reduction in the transcription of the PKC-alpha gene during differentiation. The reduced expression of this isoform corresponded with the decreased ability to activate nuclear factor kapppaB (NF-kappaB) in response to phorbol 12-myristate 13-acetate (PMA) treatment in the adipocytes. These data suggest that PMA responsiveness in 3T3-L1 adipocytes is markedly diminished.

Protein kinase C mediates tumor necrosis factor-α-induced inhibition of obese gene expression and leptin secretion in brown adipocytes

“…Although TNF receptors in brown adipocytes are not known, we suppose that the effect of TNF-α in our experiments may be mediated through binding of TNF-α on TNF receptors. Among redundant signal transductions after the stimulation of TNF receptors, PKC plays a pivotal role in adipocyte differentiation (Klip et al 1988;McGowan et al 1996) and PKC was identified in brown adipocytes (Barge et al 1988). In an attempt to investigate the role of PKC, two PKC inhibitors concentration-dependently prevented the suppressive effect of TNF-α on both ob gene expression and leptin secretion, suggesting mediation by PKC of an inhibitory effect of TNF-α on leptin secretion.…”

Blockage of PPARγ T166 phosphorylation enhances the inducibility of beige adipocytes and improves metabolic dysfunctions

“…These actions of CDDO inhibited PPARγ p-T166 and thus activated beige cell biogenesis. Furthermore, unlike PKCα inhibitor in adipocytes [ 50 , 51 ], CDDO did not impede normal adipogenesis, which suggested that targeting the PPI of PKCα-PPARγ was a safe tactic for promoting WAT browning.…”

Protein kinase C-? promotes adipogenic commitment and is essential for terminal differentiation of 3T3-F442A preadipocytes

“…Initial studies using phorbol esters, and other non-selective PKC-modulatory agents, suggested both stimulatory and inhibitory roles for PKC in the process [10][11][12][13]. More recently, the expression of specific PKC isoforms has been shown to change as preadipocytes differentiate into adipocytes [14][15][16]. The most notable and consistent of these changes are the reduction in PKC-a expression and the rise in PKC-e expression.…”