Biochimica et Biophysica Acta, 1092 (1991) 119-123 © 1991 Elsevier Science Publishers B.V. 0167-4889/91/$03.50 ADONIS 0167488991001306 119 BBAMCR 10271 BBA Report Down-regulation of protein kinase C activity in 1,2-dimethylhydrazine-induced rat colonic tumors Ramesh K. Wall, Charles L. Baum, Merry J.G. Bolt, Pradeep K. Dudeja, Michael D. Sitrin and Thomas A. Brasitus Department of Medicine, Universityof Clzicago Hospitals and Clinics, Pritzker School of Medicine, University of Chicago, Chicago, IL (U.S.A.) (Received 14 May 1990) (Revised manuscript received 5 October 1990) Key words: Diacylglycerol; Colonic cancer; Chemical carcinogenesis; Malignant transformation; Signal transduction Recent studies by our laboratory have indicated that alterations in protein kinase C activity may be involved in the early stage(s) of malignant transformation in the 1,2-dimethylhydrazine model o! colonic adenocarcinoma. In order to further evaluate the possible role of protein kinase C in this multistage process, rats were given subcutaneous weekly injections of this procarcinogen (20 mg/kg body weight) or diluent for 26 weeks. One week after receiving the last injection, animals were killed and control colonic tissue, tumor tissue and tissue at least I cm away from these tumors ('uninvolved mucosa') were harvested. The activity and distribution of protein kinase C in the cytosolic and membrane fractions of these preparations as well as their |,2-diacylglycerol mass were then examined and compared. The results of these studies demonstrated that: (1) total protein kinase C activity was reduced by approximately 35% and 60%, respectively, in the 'uninvolved' colonic mucosa and tumors of carcinogen-treated rats compared to their control counterpart values; (2) in the 'uninvolved' mucosa, this decrease in total activity was secondary to a decrease solely in cytosolic protein kinase C, whereas, in tumors both membrane and cytosolic activities were reduced; and (3) |,2-diacylglycerol mass was significantly increased in colonic tumors versus control values. Based on these findings, it would appear that alterations in the cellular distribution and total activity of protein kinase C, possibly secondary to increases in 1,2-diacyiglycerol mass, may also play a role in the latter stage(s) of malignant transformation in this experimental model Protein kinase C (PKC) is a phospholipid- and calcium-dependent serine/threonine protein kinase of fundamental importance in the regulation of normal cellular growth (reviewed in Ref. 1). Several lines of evidence exist which indicate that alterations in the activity of this ubiquitous enzyme(s) may also be in- timately involved in malignant transformation [2-10]. Rat fibroblasts transfected with p!asmids containing PKC-cDNA, for example, overproduce PKC and dem- onstrate disordered growth control and enhanced tumorigenicity [2,3]. Tumor-promoting phorbol esters have also been demonstrated to bind to and directly activate PKC [4]. Additionally, PKC appears to play a Correspondence: T.A. Brasitus, Professor of Medicine, University of Chicago Hospitals& Clinics, 5841 S. Maryland Avenue, Box 400, Chicago, IL, 60637 U.S.A. role in certain oncogene-induced transformation phe- nomena [5-8], and cells that overproduce this kinase have, in fact, been shown to be more susceptible to transformation by the activated H-ras gene [9]. Based on observations in experiments in which a mutant a- PKC gene was expressed in balb/C 3T3 fibroblasts, moreover, Megidish and Mazurek [10] have suggested that PKC genes may belong to the oncogene family. Considerable attention has also recently been given to the possible role of alterations in PKC activity in colonic carcinogenesis [11-16]. Thus, both free fatty acids [11] and bile acids [11,13], which may serve to promote colon cancer [14], have been demonstrated to enhance the activity of PKC in experimental animals and cultured cells. A reduction in the total activity of this kinase in human colonic adenocarcinomas com- pared to 'normal' adjacent colonic mucosa has also been reported [15]. Furthermore, our laboratory [16],