Lipoproteins induce expression of the early growth response gene-1 in vascular smooth muscle cells from rat.

Recently, we reported that low-density lipoprotein (LDL) induces in vascular smooth muscle cells (VSMCs) intracellular effects such as an elevation of intracellular free Ca2+ concentration ([Ca2+]i) and intracellular pH (pHi). The early growth response gene-1 (Egr-1) has been identified as a transcription factor belonging to a class of immediate-early genes expressed upon growth, and/or differentiation signals in a large variety of cells and species. Here we show that LDL induces a dose-dependent expression of the Egr-1 mRNA with a maximum at 30 min. Experiments in the presence of the dihydropyridine calcium blocker isradipine suggest that the lipoprotein-induced Egr-1 mRNA induction occurs via a Ca2+ dependent pathway. To demonstrate whether these intracellular responses are only specific to LDL we examined the effects of high- and very low density lipoprotein (HDL and VLDL) on [Ca2+]i and expression of Egr-1 mRNA. The present results show that all lipoproteins induce expression of Egr-1 mRNA and elevation in [Ca2+]i in VSMCs.