Stolz D B, Michalopoulos G K
Department of Pathology, University of Pittsburgh School of Medicine, Pennsylvania 15261.
J Cell Biochem. 1994 Aug;55(4):445-64. doi: 10.1002/jcb.240550405.
Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) are major hepatocyte mitogens, but HGF, also known as scatter factor (SF), has also been shown as a potent motogen for epithelial and endothelial cells. The mechanisms by which HGF is a stronger motogen compared to other mitogens are not understood. Here we report a comparative study of the effect of the two growth factors on cultured primary rat hepatocytes regarding their differential effects on morphology, mitogenicity, and motility as well as the phosphorylation of cytoskeletal-associated proteins. Using three different motility assays, both HGF and EGF increased the motility of hepatocytes, but HGF consistently elicited a significantly greater motility response than EGF. Additionally, HGF induced a more flattened, highly spread morphology compared to EGF. To examine if HGF and EGF phosphorylated different cytoskeletal elements as signal transduction targets in view of the observed variation in morphology and motility, primary cultures of 32P-loaded rat hepatocytes were stimulated by either HGF or EGF for up to 60 min. Both mitogens rapidly stimulated four isoforms of MAP kinase with similar kinetics and also rapidly facilitated the phosphorylation of cytoskeletal-associated F-actin. Two cytoskeletal-associated proteins, however, were observed to undergo rapid phosphorylation by HGF and not EGF during the time points described. One protein of 28 kDa was observed to become phosphorylated fivefold over controls, while the EGF-stimulated cells showed only a slight increase in the phosphorylation of this protein. Another protein with an apparent mwt of 42 kDa was phosphorylated 20-fold at 1 min and remained phosphorylated over 50-fold over control up to the 60 min time point. This protein was observed to become phosphorylated by EGF only after 10 min, and to a lesser extent (20-fold). Taken together, the data suggest that HGF and EGF stimulate divergent as well as redundant signal transduction pathways in the hepatocyte cytoskeleton, and this may result in unique HGF- or EGF-specific motility, morphology, and mitogenicity in hepatocytes.
肝细胞生长因子（HGF）和表皮生长因子（EGF）是主要的肝细胞有丝分裂原，但HGF，也被称为分散因子（SF），已被证明是上皮细胞和内皮细胞的一种强效促动因子。与其他有丝分裂原相比，HGF成为更强效促动因子的机制尚不清楚。在此，我们报告了一项关于这两种生长因子对原代培养大鼠肝细胞作用的比较研究，涉及它们在形态、有丝分裂活性和运动性以及细胞骨架相关蛋白磷酸化方面的差异效应。使用三种不同的运动性检测方法，HGF和EGF均增加了肝细胞的运动性，但HGF始终引发比EGF显著更强的运动性反应。此外，与EGF相比，HGF诱导出更扁平、高度伸展的形态。鉴于观察到的形态和运动性变化，为了研究HGF和EGF是否磷酸化不同的细胞骨架成分作为信号转导靶点，用HGF或EGF刺激32P标记的大鼠肝细胞原代培养物长达60分钟。两种有丝分裂原均以相似的动力学迅速刺激丝裂原活化蛋白激酶的四种同工型，并且也迅速促进细胞骨架相关F - 肌动蛋白的磷酸化。然而，在所述时间点观察到两种细胞骨架相关蛋白被HGF迅速磷酸化而未被EGF磷酸化。观察到一种28 kDa的蛋白磷酸化程度比对照增加了五倍，而EGF刺激的细胞中该蛋白的磷酸化仅略有增加。另一种表观分子量为42 kDa的蛋白在1分钟时磷酸化20倍，并在长达60分钟的时间点内保持比对照高50倍以上的磷酸化水平。观察到该蛋白仅在10分钟后被EGF磷酸化，且程度较小（20倍）。综上所述，数据表明HGF和EGF在肝细胞细胞骨架中刺激不同以及冗余的信号转导途径，这可能导致肝细胞中独特的HGF或EGF特异性运动性、形态和有丝分裂活性。
