PKC/Raf/MEK/ERK signaling pathway modulates native-LDL-induced E2F-1 gene expression and endothelial cell proliferation.
OBJECTIVE
The interactions of low-density lipoprotein (LDL) with the endothelium are thought to play a major role in the development of atherosclerosis. Due to this reason, the molecular sequelae of events resulting from native LDL (N-LDL) interaction with human endothelial cells (HECs) are largely under investigation.


RESULTS
Here, we report that the exposure of serum-free HECs to different concentrations of N-LDL-cholesterol (LDL-chol) elicited a time- and dose-dependent induction of DNA synthesis. The exposure of serum-free HECs to N-LDL was able to elicit a time- and dose-dependent increase of protein kinase C (PKC) activity that, along with the activation of the Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathway, leads to an increase in E2F-1 gene expression. In addition, the treatment of HECs with N-LDL was also able to induce both E2F-1 gene transcription and protein expression. These N-LDL-aroused responses were dramatically counteracted by PKC inhibition or down regulation. Similarly to what observed for Raf/MEK/ERK activation and E2F-1 gene expression, the inhibition of PKC as well as its down regulation, significantly lowered the DNA synthesis induced by N-LDL in serum-free HECs.


CONCLUSIONS
These results suggest that the activation of PKC/Raf/MEK/ERK-mediated events controlling E2F-1 gene expression by N-LDL may represent an important mechanism in the regulation of HECs proliferation during normal and pathological processes.
Pintus
Gianfranco
G
Department of Biomedical Sciences, Division of Biochemistry, Laboratory of Cardiovascular Research, University of Sassari, Viale San Pietro 43/B, 07100 Sassari, Italy. gpintus@uniss.it
Tadolini
Bruna
B
Posadino
Anna M
AM
Sanna
Bastiano
B
Debidda
Marcella
M
Carru
Ciriaco
C
Deiana
Luca
L
Ventura
Carlo
C
D018797:Cell Cycle Proteins; D002455:Cell Division; D002478:Cells, Cultured; D008078:Cholesterol, LDL / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics*
D018797:Cell Cycle Proteins; D008078:Cholesterol, LDL; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D014157:Transcription Factors; D004247:DNA; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases