Critical role of diacylglycerol- and phospholipid-regulated protein kinase C epsilon in induction of low-density lipoprotein receptor transcription in response to depletion of cholesterol.

Abstract

Induction of low-density lipoprotein (LDL) receptor transcription in response to depletion of cellular sterols in animal cells is well established. The intracellular signal or signals involved in regulating this process, however, remain unknown. Using a specific inhibitor of protein kinase C (PKC), calphostin C, we show the requirement of this kinase in the induction process in human hepatoma HepG2 cells. Overexpression of PKC epsilon, but not PKC alpha, -gamma, -delta, or -zeta was found to dramatically induce (approximately 18-fold) LDL receptor promoter activity. Interestingly, PKC epsilon-mediated induction was found to be sterol resistant. To further establish that PKC epsilon is involved in the sterol regulation of LDL receptor gene transcription, endogenous PKC epsilon was specifically inhibited by transfection with antisense PKC epsilon phosphorothionate oligonucleotides. Antisense treatment decreased endogenous PKC epsilon protein levels and completely blocked induction of LDL receptor transcription following sterol depletion. PKC epsilon-induced LDL receptor transcription is independent of the extracellular signal-regulated kinase 1 and 2 (p42/44(MAPK)) cascade, because the MEK-1/2 inhibitor, PD98059 did not inhibit, even though it blocked p42/44(MAPK) activation. Finally, photoaffinity labeling studies showed an isoform-specific interaction between PKC epsilon and sterols, suggesting that sterols may directly modulate its function by hampering binding of activators. This was confirmed by PKC activity assays. Altogether, these results define a novel signaling pathway leading to induction of LDL receptor transcription following sterol depletion, and a model is proposed to account for a new function for PKC epsilon as part of a sterol-sensitive signal transduction pathway in hepatic cells.

• Authors: Kamal D Mehta, Anna Radominska-Pandya, Gurpreet S Kapoor, Bhuvanesh Dave, Brett A Atkins
• Journal: Molecular and cellular biology (Mol Cell Biol) Vol. 22 Issue 11 Pg. 3783-93 (Jun 2002) ISSN: 0270-7306 [Print] United States
• PMID: 11997513 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Diglycerides
• Eicosanoids
• Isoenzymes
• Oligodeoxyribonucleotides, Antisense
• Phospholipids
• Receptors, LDL
• Recombinant Proteins
• Cholesterol
• PRKCE protein, human
• Protein Kinase C
• Protein Kinase C-epsilon
• Mitogen-Activated Protein Kinases
• Type C Phospholipases

Topics

• Animals
• Cholesterol (metabolism)
• Diglycerides (metabolism)
• Eicosanoids (metabolism)
• Gene Expression
• Humans
• Isoenzymes (genetics, metabolism)
• Mitogen-Activated Protein Kinases (metabolism)
• Models, Biological
• Oligodeoxyribonucleotides, Antisense (genetics, pharmacology)
• Phospholipids (metabolism)
• Protein Kinase C (genetics, metabolism)
• Protein Kinase C-epsilon
• Receptors, LDL (biosynthesis, genetics)
• Recombinant Proteins (genetics, metabolism)
• Signal Transduction
• Transcription, Genetic
• Tumor Cells, Cultured
• Type C Phospholipases (metabolism)