Abstract
Phospholipase C (PLC), Which hydrolyzes phosphoinositides, has been implicated as a key enzyme in signal transduction. We examined the expression of an isozyme of PLC, PLC,‐δ, in rat colon neoplasms induced by methylazoxymethanol (MAM) acetate. Large‐bowel neoplasms were observed in five of 10 rats given MAM acetate (25 mg/kg body weight, by interperitoneal injection at 6 and 7 wk of age) 40 wk after treatment. Expression of PLC‐δ in the neoplasms was not detected by northern blot analysis, and a low level of expression was detected by immunoblot analysis, although PLC‐δ expression was apparent in the non‐neoplastic colon mucosae of MAM acetate‐treated rats as well as in the colon mucosae of control rats. Furthermore, analysis by reverse transcriptase‐polymerase chain reaction revealed that the ratio of the expression of PLC‐δ to that of β‐action in the neoplasms was significantly lower than the ratios in the non‐neoplastic colon mucosae of carcinogen‐treated and control rats (P<0.01) However, the ornithine decarboxylase (ODC) activity in the neoplsms was significantly greater than that of the non‐neoplastic and control mucosae (P<0.001). The differences in the levels of PLC‐δ expression in neoplastic and non‐neoplastic tissues and the inverse correlation of PLC‐δ expression with ODC activity may suggest that PLC‐δ has little effect on the PLC‐mediated mitogenic signaling system, at least in MAM acetate‐induced colon neoplasms in rats.