DIFFERENTIATION OF PANCREATIC DUCTAL CARCINOMA-CELLS ASSOCIATED WITH SELECTIVE EXPRESSION OF PROTEIN-KINASE-C ISOFORMS

Background: The signal transduction pathways important in regulating t he growth and differentiation of malignant cells an poorly: understood , Recent evidence has implicated activation of the protein kinase C (P KC) family of signaling proteins in pancreatic carcinoma during cytoki ne-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-te trazolium bromide] and trypan exclusion assay, Protein fractions were isolated daily and subjected to immunoblot analysis for the normal (te rminallp difderentiated) pancreatic duclal cell marker carbonic anhydr ase II (CA Il) as well as specific PKC isoforms (alpha, beta, gamma, e ta, and zeta. Results: Growth arrest occurred in HPAC cells after expo sure to TNF-alpha for 48 h, with viability maintained above 90% throug hout the 6-day time course. CA II immunoreactivity was not detected in untreated controls bur appeared after 2 days of TNF-alpha exposure, p eaking on day 6. Concurrently, TNF-alpha induced the selective downreg ulation of PKC-alpha, whereas PKC-gamma levels increased. PKC-beta and PKC-eta immunoreactivity did nor change. The atypical PKC-zeta isofor m developed a doublet banding pattern in response to TNF-alpha, althou gh overall PKC-zeta levels did not change. Conclusions: TNF-alpha-indu ced growth arrest and differentiation in HPAC cells is associated with the selective downregulation of PKC-alpha and upregulation of PKC-gam ma.