Potentiation of oncogenic N-ras-induced neurite outgrowth and ornithine decarboxylase activity by phorbol dibutyrate and protein kinase inhibitor H-8.
A recombinant N-ras oncogene, under the transcriptional control of a corticosteroid-inducible mouse mammary tumor virus (MMTV) promoter, has been stably transfected into a PC12 rat pheochromocytoma subline. This cell line, designated UR61, undergoes N-ras-induced neurite outgrowth and cessation of division when treated with dexamethasone (Guerrero et al.: Biochemical and Biophysical Research Communications 150:1185-1192, 1988). We have employed the UR61 cell line as a model for ras oncogene-induced neuronal differentiation. In UR61 cells, dexamethasone-induced expression of the recombinant N-ras gene resulted in time-dependent expression of ornithine decarboxylase enzyme (ODC) activity. Prompted by recent reports of possible functional (Lacal et al.: Molecular and Cellular Biology 7:4146-4149, 1987; Wolfman and Macara: Nature 325: 359-361, 1987) and direct (Jeng et al.: Biochemical and Biophysical Research Communications 145:782-788, 1987) interactions between oncogene ras-coded p21 and protein kinase C (PK-C; Ca++/phospholipid-dependent protein kinase), we employed the protein kinase inhibitor H-8 (N-[2-(methylamino)ethyl]-5-isoquinoline sulfonamide dihydrochloride) and phorbol 12,13-dibutyrate (PDBu) to investigate this putative interaction in the UR61 cells, where ODC activity and neurite outgrowth were used as indicators of oncogenic N-ras action. Treatment of UR61 cells with PDBu depleted cells of PK-C and failed to promote neurite outgrowth but enhanced N-ras-induced neurite outgrowth and ODC activity. H-8, which suppressed ODC induction by forskolin and phorbol myristate acetate, enhanced both N-ras-induced ODC activity and neurite outgrowth. Inhibition of ODC activity by difluoromethylornithine (DFMO) did not suppress oncogenic ras-induced neurite outgrowth, suggesting that these two ras-triggered events are mechanistically independent. These findings suggest that certain actions of N-ras can occur in cells depleted of PK-C, and thus, the role of PK-C in ras-induced differentiation differs from its role in ras-induced mitogenesis and transformation.
Trotta
R J
RJ
Department of Pathology, New York University School of Medicine, New York 10016.
Thomson
T M
TM
Lacal
J C
JC
Pellicer
A
A
Burstein
D E
DE
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D005576:Colforsin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology*; D009414:Nerve Growth Factors / Q000494:pharmacology; D009474:Neurons / Q000166:cytology*; D015689:Oncogene Protein p21(ras) / Q000502:physiology*; D009955:Ornithine Decarboxylase / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000502:physiology; D047428:Protein Kinase Inhibitors; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D007546:Isoquinolines; D009414:Nerve Growth Factors; D047428:Protein Kinase Inhibitors; D005576:Colforsin; D015240:Phorbol 12,13-Dibutyrate; D014212:Tretinoin; D004815:Epidermal Growth Factor; D003907:Dexamethasone; C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D011493:Protein Kinase C; D015689:Oncogene Protein p21(ras); D009955:Ornithine Decarboxylase; D013755:Tetradecanoylphorbol Acetate