Very low density lipoprotein receptor （VLDLR） is thought to participate in the pathogenesis of atherosclerosis induced by VLDL and β-VLDL. The present study was undertaken to elucidate the effects of VLDL and β-VLDL on VLDLR expression and its signaling pathway. RAW264.7 cells were incubated with VLDL and β-VLDL. The expression of VLDLR mRNA was detected by RT-PCR. The transcriptional activity of VLDLR gene was detected in recombinant plasmid pGL4.2VR-luciferase transfected RAW264.7. Western blot assay was used to detect the changes of phosphorylated ERK1/2 protein. Inhibitors or activators were used to observe the signal pathway involving VLDLR expression regulation. The results showed that VLDL and β-VLDL stimulated ERK1/2 activity in a PKC-dependent manner. VLDL or β-VLDL-induced VLDLR expression on macrophages was extremely abolished by inhibitors ERK1/2 or PKC. Our findings revealed that VLDL or β-VLDL-induced VLDLR expression via PKC/ERK cascades and the effect was linked to the transcriptional activation of VLDLR gene promoter.
In order to construct the expression recombinant of human receptor associated protein （RAP）, optimize its expression condition and obtain the recombinant protein after expression with high efficiency, two prokaryotic expression vectors-pT7-PL and pET-28a（＋） were used to construct the expression recombinant containing RAP cDNA, and the expression efficiency of two kinds of expression E. coli of BL21 strains was compared. The effect of different induction conditions on the expression of recombinant RAP was observed. After recombinant protein was purified with Ni^＋ -nitrilotriacetic acid （Ni^＋ -NTA） affinity chromatogram, its binding ability with microphage was observed. The results showed that two recombinant plasmids both obtained high expression of RAP. The expression levels of RAP in plasmid pT7-PL-RAP in BL21 （DE3, plysS） strain were significantly higher than in BL21 （DE3） strain. The expression of pT7-PL-RAP in the presence of chloramphenicol was higher than in the absence of chloramphenicol, and most of the inducible expressed RAP was soluble. The RAP which was purified by Ni^＋ -NTA resin could strongly bind with the RAW264.7 cells rich in low density lipoprotein receptor （LDLR） family receptors. It was concluded that the expression condition of recombinant RAP was optimized and functional RAP was obtained, which offered a good foundation for the further production of RAP as research tool.
This study examined the effect of insulin on the expression of very low density lipoprotein receptor (VLDLR) subtypes of SGC7901 cells and discussed its biological implication.In vitro, moderately or poorly-differentiated human gastric adenocarcinoma cell line SGC7901 was incubated with insulin for different lengths of time, and then the expression of protein and RNA level in VLDLR subtypes were detected by Western blotting and real-time PCR, respectively.The results showed that, at certain time interval, insulin could down-regulate expression of type Ⅰ VLDLR and up-regulate the expression of type Ⅱ VLDLR in SGC7901 cells, at both protein and RNA level.We are led to conclude that insulin serves as a regulator in maintaining the balance between glucose and lipid metabolism in vivo, possibly through its effect on the differential expression of VLDLR subtypes.
