title: Choline deficiency activates phospholipases A2 and C in rat liver without affecting the activity of protein kinase C.
abstract: There is evidence to suggest that liver tumor promoters exert their effect through the interference of signal transduction in hepatic cells. Both phospholipase A(2) and phospholipase C play important roles in the generation of second messengers and in the activation of Ca(2+), 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(2) 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 A(2) (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 A(2) activities at 4 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 A(2) 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 of protein kinase C under the present experimental condition.
authors.affiliation: Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
authors.forename: U
authors.initials: U
authors.lastname: Singh
authors.forename: K
authors.initials: K
authors.lastname: Yokota
authors.forename: C
authors.initials: C
authors.lastname: Gupta
authors.forename: H
authors.initials: H
authors.lastname: Shinozuka