Expression of G protein alpha subunits in normal rat colon and in azoxymethane-induced colonic neoplasms.
OBJECTIVE
Heterotrimeric G proteins are important in growth-regulating signal transduction. The aim of this study was to characterize the relative expression of G protein alpha subunits in rat colonocytes, colonocyte antipodal plasma membranes, and colonic neoplasms.


METHODS
Antipodal plasma membranes were prepared from isolated colonocytes. Azoxymethane was administered to rats to induce colonic neoplasms. K-ras mutations in the neoplasms were determined by oligonucleotide hybridization and confirmed by primer mediated-restriction fragment length polymorphism. Colonocyte and tumor homogenates or membranes were probed for Galpha subunits by Western blotting with isoform-specific antibodies.


RESULTS
The expressions of Galphai2, alphai3, and alphaq/11 were significantly enriched in the basolateral compared with brush border fraction of colonic antipodal plasma membranes. In neoplasms without K-ras mutations, the expression of Galphai2 increased 4-fold, Galphas(long) increased 2.5-fold, and Galphai3 increased 1.5-2-fold. Expression did not differ among tumor grades. K-ras mutations were associated with lowered expression of G proteins, especially Galphao.


CONCLUSIONS
In colonocytes, Galpha subunits are localized primarily in basolateral plasma membranes. The increased expressions of Galphai2 and, to a lesser degree, Galphai3 and Galphas(long) in tumors was independent of tumor grade but was modulated by the presence of K-ras mutations.
Bolt
M J
MJ
Department of Medicine, University of Chicago, Chicago, Illinois, 60637, USA.
Mailloux
R J
RJ
Rasenick
M M
MM
Wali
R K
RK
Skarosi
S
S
Bissonnette
M
M
Brasitus
T A
TA
Sitrin
M D
MD
D000818:Animals; D001397:Azoxymethane; D003106:Colon / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000096:biosynthesis*; D011905:Genes, ras; D008297:Male; D009154:Mutation; D051381:Rats; D017207:Rats, Sprague-Dawley
D019204:GTP-Binding Proteins; D001397:Azoxymethane