Blasband A J, Gilligan D M, Winchell L F, Wong S T, Luetteke N C, Rogers K T, Lee D C
Lineberger Cancer Research Center, University of North Carolina, Chapel Hill 27599-7295.
Oncogene. 1990 Aug;5(8):1213-21.
TGF alpha is one member of a family of soluble growth factors that are derived from integral-membrane precursors. The mature form of TGF alpha is released from its transmembrane precursor (proTGF alpha) by a protease that, in many tumor cells, is inefficient or limiting. We have previously established that, in the absence of processing, membrane-anchored proTGF alpha is biologically active and can interact with the EGF receptor on adjacent cells, thereby inducing the receptor's intrinsic tyrosine kinase activity. We further showed that this interaction leads to immediate downstream signal transduction as evidenced by Ca2+ mobilization. To extend these observations, and to investigate its transforming potential, we infected normal rat kidney (NRK) cells with retroviral expression vectors that encode mutated forms of proTGF alpha containing amino acid substitutions at the proteolytic cleavage sites. NRK cells harboring these mutant constructs do not secrete mature growth factor, but do express biologically active proTGF alpha on the cell surface as shown by their ability to induce the autophosphorylation of EGF receptor on neighboring A431 cells in co-culture. Expression of the mutant proTGF alpha molecules promoted the anchorage-independent growth of NRK cells in soft agar, and caused them to be tumorigenic when injected into nude mice. These results demonstrate that an interaction between EGF receptor and the integral membrane precursor to TGF alpha can provide a mitogenic stimulus that leads to transformation. They further suggest that the accumulation of proTGF alpha on the surface of some transformed cells has physiological relevance.
转化生长因子α（TGFα）是一类可溶性生长因子家族的成员，这些生长因子来源于整合膜前体。TGFα的成熟形式是通过一种蛋白酶从其跨膜前体（前TGFα）释放出来的，而在许多肿瘤细胞中，这种蛋白酶的活性较低或受到限制。我们之前已经确定，在没有加工的情况下，膜锚定的前TGFα具有生物活性，并且可以与相邻细胞上的表皮生长因子（EGF）受体相互作用，从而诱导受体的内在酪氨酸激酶活性。我们进一步表明，这种相互作用导致了如钙离子动员所证明的直接下游信号转导。为了扩展这些观察结果，并研究其转化潜力，我们用逆转录病毒表达载体感染正常大鼠肾（NRK）细胞，这些载体编码在蛋白水解切割位点含有氨基酸取代的前TGFα突变形式。携带这些突变构建体的NRK细胞不分泌成熟生长因子，但在细胞表面表达具有生物活性的前TGFα，这通过它们在共培养中诱导相邻A431细胞上EGF受体自磷酸化的能力得以证明。突变前TGFα分子的表达促进了NRK细胞在软琼脂中不依赖贴壁的生长，并在注射到裸鼠体内时使其具有致瘤性。这些结果表明，EGF受体与TGFα的整合膜前体之间的相互作用可以提供一种促有丝分裂刺激，从而导致细胞转化。它们进一步表明，前TGFα在一些转化细胞表面的积累具有生理相关性。
