FIG. 7.

Effects of high-dose TPA treatment on the time-dependent degradation of selective PKC isoforms and on the level of induction of endogenous LDL receptor expression in response to depletion of sterols. HepG2 cells were grown in either 10% LPDS or 10% LPDS plus sterols in the continued presence of 1 μM TPA. Expression of PKC isoforms was detected at the indicated time periods by Western blot analysis of HepG2 cell lysates. Total RNA was isolated after 24 h of treatment and subjected to Northern blotting to determine amounts of LDL receptor and actin mRNAs. Autoradiographs obtained after longer exposures were quantitated densitometrically. LDL receptor mRNA levels were normalized to actin mRNA levels. Results are expressed as X-fold induction by depletion of sterols as compared with cells grown in the presence of sterols (10% LPDS plus sterols).