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Mol Cell Biol, July 1998, p. 3718-3726, Vol. 18, No. 7
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Differential Effects of Protein Kinase A on Ras Effector Pathways

Marsha J. Miller,1 Lise Rioux,1 Gregory V. Prendergast,1 Sarah Cannon,2 Michael A. White,3 and Judy L. Meinkoth1 *

Department of Medicine and Therapeutics, University College Dublin, Dublin 7, Ireland2; Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas 752353; and Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-60841

Received 17 December 1997/Returned for modification 1 February 1998/Accepted 26 March 1998

Ras mutants with the ability to interact with different effectors have played a critical role in the identification of Ras-dependent signaling pathways. We used two mutants, RasS35 and RasG37, which differ in their ability to bind Raf-1, to examine Ras-dependent signaling in thyroid epithelial cells. Wistar rat thyroid cells are dependent upon thyrotropin (TSH) for growth. Although TSH-stimulated mitogenesis requires Ras, TSH activates protein kinase A (PKA) and downregulates signaling through Raf and the mitogen-activated protein kinase (MAPK) cascade. Cells expressing RasS35, a mutant which binds Raf, or RasG37, a mutant which binds RalGDS, exhibited TSH-independent proliferation. RasS35 stimulated morphological transformation and anchorage-independent growth. RasG37 stimulated proliferation but not transformation as measured by these indices. TSH exerted markedly different effects on the Ras mutants and transiently repressed MAPK phosphorylation in RasS35-expressing cells. In contrast, TSH stimulated MAPK phosphorylation and growth in cells expressing RasG37. The Ras mutants, in turn, exerted differential effects on TSH signaling. RasS35 abolished TSH-stimulated changes in cell morphology and thyroglobulin expression, while RasG37 had no effect on these activities. Together, the data indicate that cross talk between Ras and PKA discriminates between distinct Ras effector pathways.

* Corresponding author. Mailing address: Department of Pharmacology, University of Pennsylvania School of Medicine, 36th St. and Hamilton Walk, Philadelphia, PA 19104-6084. Phone: (215) 898-1909. Fax: (215) 573-2236. E-mail: meinkoth{at}pharm.med.upenn.edu.

Mol Cell Biol, July 1998, p. 3718-3726, Vol. 18, No. 7
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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