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-α (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-α isoform was reduced by 85% as cells attained the adipocyte phenotype. PKC-β expression was measurable only during the early stages of the differentiation process and was not detectable in fully differentiated cells. An upregulation of PKC-θ, a novel PKC isoform, occurred during the latter stage of differentiation. Expression of PKC-ζ 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 ≅ 85% reduction in the transcription of the PKC-α gene during differentiation. The reduced expression of this isoform corresponded with the decreased ability to activate nuclear factor κB (NF-κB) 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. © 1996 Wiley-Liss, Inc.