G[alpha]i-2 mediates renal llc-pk1 growth by a raf independent activation of p42/p44 map kinase. Kinane, T. Bernard, I. Kang, A. Chu, S. H. Chin, and Louis Ercolani. Departments of Medicine and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114
APStracts 3:0222F, 1996.
The protooncogene G[alpha]i-2 plays a pivotal role in signaling pathways that control renal cell growth and differentiation. Mitogen activated protein kinases (MAPKs) are potential downstream effectors for G[alpha]i-2 in these pathways. In pre-differentiated LLC-PK1 renal cells, the temporal maximal expression of G[alpha]i-2 coincided with maximal activation of MAPK(p42/p44). By contrast pertussis toxin treatment of these cells, inhibited cell growth and reduced MAPK(p42/p44) activity by 30%. These findings reflected upstream activation of MAPK kinase (MEK1), as transient transfection of cells with a plasmid encoding a constitutively active form of MEK1 increased MAPK(p42/p44) activity and cell growth., whereas treatment with PD 098059, an inhibitor of MEK1 activity, reduced MAPK(p42/p44) activity and cell growth. Expression of a GTPase deficient G[alpha]i -2 in these cells increased MAPK(p42/p44) activity and correspondingly reduced cell doubling time from 24 to 10 hrs without altering the activity of Raf-1 or c-Jun/stress-activated protein kinases (SAPKs). By contrast, expression of a GTPase deficient G[alpha]i-3 in these cells reduced both their cell doubling time by 30% and MAPK(p42/p44) activity by 60%. As the known MEKK isoforms (MEKK 1,2, and 3) can also activate SAPKs, these findings suggest the GTP charged G[alpha]i-2 subunit transduces growth signals in renal cells via activation of MAPK(p42/p44) and that such activation may be linked to pathways containing novel MEKK isoforms that preferentially activate MEKs. 

Received 9 October 1996; accepted in final form 26 November 1996.
APS Manuscript Number F283-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996