Vega Q C, Cochet C, Filhol O, Chang C P, Rhee S G, Gill G N
Department of Biology, School of Medicine, University of California, San Diego, La Jolla 92093-0650.
Mol Cell Biol. 1992 Jan;12(1):128-35. doi: 10.1128/mcb.12.1.128-135.1992.
Cells expressing mutant epidermal growth factor (EGF) receptors have been used to study mechanisms through which EGF increases phospholipase C (PLC) activity. C-terminal truncation mutant EGF receptors are markedly impaired in their ability to increase inositol phosphate formation compared with wild-type EGF receptors. Mutation of the single tyrosine self-phosphorylation site at residue 992 to phenylalanine in an EGF receptor truncated at residue 1000 abolished the ability of EGF to increase inositol phosphate formation. C-terminal deletion mutant receptors that are impaired in their ability to increase inositol phosphate formation effectively phosphorylate PLC-gamma at the same tyrosine residues as do wild-type EGF receptors. EGF enhances PLC-gamma association with wild-type EGF receptors but not with mutant receptors lacking sites of tyrosine phosphorylation. These results indicate that formation of a complex between self-phosphorylated EGF receptors and PLC-gamma is necessary for enzyme activation in vivo. We propose that both binding of PLC-gamma to activated EGF receptors and tyrosine phosphorylation of the enzyme are necessary to elicit biological responses. Kinase-active EGF receptors lacking sites of tyrosine phosphorylation are unable to signal increased inositol phosphate formation and increases in cytosolic Ca2+ concentration.
表达突变型表皮生长因子（EGF）受体的细胞已被用于研究EGF增加磷脂酶C（PLC）活性的机制。与野生型EGF受体相比，C末端截短的突变型EGF受体在增加肌醇磷酸形成的能力上明显受损。在截短至第1000位残基的EGF受体中，将第992位残基处的单个酪氨酸自磷酸化位点突变为苯丙氨酸，消除了EGF增加肌醇磷酸形成的能力。在增加肌醇磷酸形成能力上受损的C末端缺失突变型受体，能像野生型EGF受体一样有效地在相同的酪氨酸残基上磷酸化PLC-γ。EGF增强PLC-γ与野生型EGF受体的结合，但不增强其与缺乏酪氨酸磷酸化位点的突变型受体的结合。这些结果表明，自磷酸化的EGF受体与PLC-γ之间形成复合物对于体内酶的激活是必需的。我们提出，PLC-γ与活化的EGF受体的结合以及该酶的酪氨酸磷酸化对于引发生物学反应都是必需的。缺乏酪氨酸磷酸化位点的激酶活性EGF受体无法发出增加肌醇磷酸形成和增加胞质Ca2+浓度的信号。
