Relationship of bile salt stimulation of colonic epithelial phospholipid turnover and proliferative activity: role of activation of protein kinase C1.

The mechanism by which bile salts stimulate the proliferative activity of colonic epithelium is uncertain. One of the striking cellular actions of certain bile salts that enhance the proliferative activity of colonic epithelium, such as deoxycholate (DOC) and chenodeoxycholate, is the rapid stimulation of membrane phospholipid turnover. Increased membrane phosphoinositol turnover may lead to release of diacylglycerol (DAG). The latter is an endogenous activator of the calcium phospholipid-dependent enzyme protein kinase C (PKC) whose stimulation has been correlated with enhanced proliferation in several cell systems. In the present study, we examined the effects of DOC on PKC of colonic epithelium in vitro and in vivo. When added directly in vitro to partially purified soluble preparations of phospholipid, calcium-dependent PKC from crypts isolated from rat colon, DOC suppressed activity by 20%, presumably due to calcium complex formation. By contrast, the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), and the DAG derivative, 1-oleoyl-2-acetylglycerol (OAG), increased soluble PKC in vitro twofold. The nontumor promoters phorbol and 4 alpha-phorbol-12,13-didecanoate (4 alpha PDD) were without effect. However, in intact colonic epithelial crypt cells prelabeled with arachidonate, DOC caused rapid release of DAG and markedly increased the fraction of PKC associated with the particulate cell fraction, an index of PKC activation. TPA and OAG caused similar shifts in the subcellular distribution of PKC but did not stimulate DAG release, whereas phorbol and 4 alpha PDD were without effect on any parameter. In vivo intracolonic instillation of DOC, OAG, or TPA each induced a shift of soluble PKC to the particulate fraction of colonic mucosal scrapings.(ABSTRACT TRUNCATED AT 250 WORDS)