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 are 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 (terminally differentiated) pancreatic ductal cell marker carbonic anhydrase II (CA II) 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 but 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 not 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.
Department of Surgery, University of South Florida College of Medicine, Tampa, USA.
M G
MG
Franz
J G
JG
Norman
P J
PJ
Fabri
W R
WR
Gower
D002256:Carbonic Anhydrases / Q000032:analysis; D018270:Carcinoma, Ductal, Breast / Q000201:enzymology* / Q000473:pathology*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D006801:Humans; D007527:Isoenzymes / Q000032:analysis*; D010190:Pancreatic Neoplasms / Q000201:enzymology* / Q000473:pathology*; D011493:Protein Kinase C / Q000032:analysis*; D064546:Protein Kinase C beta; D051571:Protein Kinase C-alpha; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D000099221:Protein Kinase C zeta
D002256:Carbonic Anhydrases; D007527:Isoenzymes; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D051571:Protein Kinase C-alpha; D014409:Tumor Necrosis Factor-alpha; D000099221:Protein Kinase C zeta; C081975:protein kinase C eta; C087857:protein kinase C gamma; C496628:PRKCA protein, human