Choline deficiency activates phospholipases A2 and C in rat liver without affecting the activity of protein kinase C.
Singh U. | Yokota K. | Gupta C. | Shinozuka H.
There is evidence to suggest that liver tumor promoters exert their effect through the interference of signal transduction in hepatic cells. Both phospholipase A2 and phospholipase C play important roles in the generation of second messengers and in the activation of Ca2+, phospholipid-dependent protein kinase C. Using male Sprague-Dawley rats, we investigated whether liver tumor-promoting regimens of a choline-deficient diet and phenobarbital alter the activities of phospholipase A, and phospholipase C in the liver, and extended the study to determine the effect of a choline-deficient diet on protein kinase C activities. Feeding a choline-deficient diet for 1 week increased the activities of both phospholipase A2 (50%) and phospholipase C (22%), and the activities of both enzymes were more than doubled after 4 weeks. Feeding a phenobarbital diet resulted in a slight decrease in phospholipase A2 activities at 4 it weeks but no significant changes in PLC activities. The protein kinase C activities and its distribution between soluble and particulate fractions remained unchanged after 1, 2, and 4 weeks feeding of a choline-deficient diet. Thus, activation of both phospholipase A2 and C is distinct for a choline-deficient diet, not shared by phenobarbital diet. Increased activities of these enzymes were not associated with the activation protein kinase C under the present experimental condition.
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