Differentiation of pancreatic ductal carcinoma cells associated with selective expression of protein kinase C isoforms

Background: The signal transduction pathways important in regulating the growth and differentiation of malignant cells an poorly: understood, Recent evidence has implicated activation of the protein kinase C (PKC) family of signaling proteins in pancreatic carcinoma during cytokine-induced cytostasis and differentiation. Methods: A human pancreatic adenocarcinoma (HPAC) cell line was exposed to tumor necrosis factor-alpha (TNF-alpha; 40 ng/ml) for 6 days. Cytostasis and viability were confirmed by daily MTT [(3(4,5)-dimethyl-thiazol-2-yl) 2,5-diphenyl-tetrazolium bromide] and trypan exclusion assay, Protein fractions were isolated daily and subjected to immunoblot analysis for the normal (terminallp difderentiated) pancreatic duclal cell marker carbonic anhydrase II (CA Il) as well as specific PKC isoforms (alpha, beta, gamma, eta, and zeta. Results: Growth arrest occurred in HPAC cells after exposure to TNF-alpha for 48 h, with viability maintained above 90% throughout the 6-day time course. CA II immunoreactivity was not detected in untreated controls bur appeared after 2 days of TNF-alpha exposure, peaking on day 6. Concurrently, TNF-alpha induced the selective downregulation of PKC-alpha, whereas PKC-gamma levels increased. PKC-beta and PKC-eta immunoreactivity did nor change. The atypical PKC-zeta isoform developed a doublet banding pattern in response to TNF-alpha, although overall PKC-zeta levels did not change. Conclusions: TNF-alpha-induced growth arrest and differentiation in HPAC cells is associated with the selective downregulation of PKC-alpha and upregulation of PKC-gamma.