Mjg. Bolt et al., Expression of G protein alpha subunits in normal rat colon and in azoxymethane-induced colonic neoplasms, GASTROENTY, 115(6), 1998, pp. 1494-1503
Background & Aims: Heterotrimeric G proteins are important in growth-regula
ting signal transduction. The aim of this study was to characterize the rel
ative expression of G protein a subunits in rat colonocytes, colonocyte ant
ipodal plasma membranes, and colonic neoplasms. Methods: Antipodal plasma m
embranes were prepared from isolated colonocytes, Azoxymethane was administ
ered to rats to induce colonic neoplasms. K-ras mutations in the neoplasms
were determined by oligonucleotide hybridization and confirmed by primer me
diated-restriction fragment length polymorphism. Colonocyte and tumor homog
enates or membranes were probed for G alpha subunits by Western blotting wi
th isoform-specific antibodies. Results: The expressions of G alpha i2, alp
ha i3, and alpha q/11 were significantly enriched in the basolateral compar
ed with brush border fraction of colonic antipodal plasma membranes. In neo
plasms without K-ras mutations, the expression of G alpha i2 increased 4-fo
ld, G alpha s(long) increased 2.5-fold, and G alpha i3 increased 1.5-2-fold
. Expression did not differ among tumor grades. K-ras mutations were associ
ated with lowered expression of G proteins, especially G alpha o. Conclusio
ns: In colonocytes, G alpha subunits are localized primarily in basolateral
plasma membranes. The increased expressions of G alpha i2 and, to a lesser
degree, G alpha i3 and G alpha s(long) in tumors was independent of tumor
grade but was modulated by the presence of K-ras mutations.