Hsu H Y, Nicholson A C, Hajjar D P
Department of Biochemistry, Cornell University Medical College, New York, New York 10021.
J Biol Chem. 1994 Mar 25;269(12):9213-20.
Basic fibroblast growth factor (bFGF) has been implicated in the regulation of cell proliferation and cholesterol metabolism. In studies reported herein, we show bFGF increases low density lipoprotein (LDL) binding, uptake, and degradation in arterial smooth muscle cells in a dose-dependent manner. This increase was paralleled by an increase in LDL receptor mRNA steady state levels. To determine if bFGF activated transcription of the LDL receptor gene, we transiently transfected smooth muscle cells with a gene construct consisting of the 5'-upstream promoter region of the DNA from the human LDL receptor gene ligated to a plasmid containing the luciferase gene. We found that bFGF and a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate, significantly induced luciferase activity driven by the LDL receptor promoter, whereas 25-hydroxycholesterol reduced the luciferase activity in bFGF-stimulated cells. These findings show that bFGF and PKC are inducing LDL receptor gene transcription. We also evaluated potential signal transduction pathways induced by bFGF to establish the mechanism(s) leading to the activation of the LDL receptor gene. Activation of the activity of FGF receptor tyrosine kinase in smooth muscle cells by ligand binding resulted in tyrosine phosphorylation of one of the FGF receptors and a 90-kDa-protein as well as increased tyrosine phosphorylation of phospholipase C-gamma. Parallel observations were made in that increased PKC and protein kinase A activities occurred with bFGF as compared with control cells. Inhibitors of receptor tyrosine kinase and other protein kinases significantly reduced transcription and surface expression of LDL receptor. Finally, several key enzymes that are central to the regulation of LDL-cholesteryl ester metabolism were also studied in bFGF-stimulated cells. An increase in acyl-CoA:cholesterol acyltransferase activity and cholesterol esterification was observed with bFGF stimulation, but there was no effect on the lysosomal or cytoplasmic cholesteryl ester hydrolase activities. Our findings suggest potential signal transduction pathways activated by bFGF which play a role in regulating transcription and surface expression of the LDL receptor.
碱性成纤维细胞生长因子（bFGF）与细胞增殖和胆固醇代谢的调节有关。在本文报道的研究中，我们发现bFGF以剂量依赖的方式增加动脉平滑肌细胞中低密度脂蛋白（LDL）的结合、摄取和降解。这种增加与LDL受体mRNA稳态水平的增加平行。为了确定bFGF是否激活了LDL受体基因的转录，我们用一个基因构建体瞬时转染平滑肌细胞，该构建体由人LDL受体基因DNA的5'-上游启动子区域与一个含有荧光素酶基因的质粒连接而成。我们发现bFGF和一种蛋白激酶C（PKC）激活剂，佛波酯12-肉豆蔻酸酯13-乙酸酯，显著诱导由LDL受体启动子驱动的荧光素酶活性，而25-羟基胆固醇降低了bFGF刺激细胞中的荧光素酶活性。这些发现表明bFGF和PKC正在诱导LDL受体基因转录。我们还评估了bFGF诱导的潜在信号转导途径，以确定导致LDL受体基因激活的机制。配体结合激活平滑肌细胞中FGF受体酪氨酸激酶的活性，导致一种FGF受体和一种90 kDa蛋白的酪氨酸磷酸化，以及磷脂酶C-γ的酪氨酸磷酸化增加。与对照细胞相比，bFGF处理的细胞中PKC和蛋白激酶A的活性也有类似增加。受体酪氨酸激酶和其他蛋白激酶的抑制剂显著降低了LDL受体的转录和表面表达。最后，我们还研究了bFGF刺激细胞中对LDL-胆固醇酯代谢调节至关重要的几种关键酶。bFGF刺激后观察到酰基辅酶A：胆固醇酰基转移酶活性和胆固醇酯化增加，但对溶酶体或细胞质胆固醇酯水解酶活性没有影响。我们的发现表明bFGF激活的潜在信号转导途径在调节LDL受体的转录和表面表达中发挥作用。
