ras-Transformation of MDCK cells alters responses to phorbol ester without altering responses to bradykinin
✍ Scribed by Sandra R. Slivka; Catherine Godson; Paul A. Insel
- Publisher
- John Wiley and Sons
- Year
- 1990
- Tongue
- English
- Weight
- 766 KB
- Volume
- 42
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
The results of studies to evaluate the hypothesis that the 21 kDa GTP-binding protein derived from the rus oncogene is involved in regulation and coupling of hormone receptors to phospholipase activity have thus far been inconsistent. We therefore examined the effect of H-rus transformation on basal, tumor-promoting phorbol ester (TPA)-stimulated, and bradykinin-mediated phospholipid hydrolysis in Madin Darby canine kidney cells (MDCK) by comparing H-ras-transformed MDCK cells (MDCK-RAS) to two non-transformed strains of MDCK cells (MDCK-D1 and MDCK-ATCC). In unstimulated MDCK-RAS, diacylglycerol (DAG), inositol phosphate accumulation, and choline phosphate release were increased while arachidonic acid and arachidonic acid metabolite (AA) release was not increased, suggesting that ras transformation increased phospholipase C activity. Protein kinase C (PK-C) activity was decreased, and specific binding of [3H]phorbol ester was reduced in MDCK-RAS relative to the non-transformed MDCK cells suggesting that elevated DAG may activate and thereby down-regulate PK-C. Consistent with this finding in MDCK-RAS, TPA-stimulated AA release and subsequent prostaglandin E, production were decreased, while TPA-stimulated choline phosphate release was increased. Bradykinin receptor-stimulated phospholipid hydrolysis in MDCK-RAS was similar to that of non-transformed cells, suggesting that the rus-derived protein does not directly couple bradykinin receptors to phospholipases in MDCK cells. However, the ability of TPA-treatment to inhibit bradykinin-stimulated phosphoinositide hydrolysis and enhance bradykinin-stimulated AA release was attenuated in MDCK-RAS.