Phosphotyrosine binding domain-dependent upregulation of the platelet-derived growth factor receptor alpha signaling cascade by transforming mutants of Cbl: Implications for Cbl's function and oncogenicity
Phosphotyrosine binding domain-dependent upregulation of the platelet-derived growth factor receptor alpha signaling cascade by transforming mutants of Cbl: Implications for Cbl's function and oncogenicity
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DOI：
10.1128/mcb.17.8.4597
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发表时间：
1997-08-01
影响因子：
5.3
通讯作者：
Band, H
中科院分区：
文献类型：
--
作者：
Bonita, DP;Miyake, S;Band, H
最近的研究表明，Cbl，c-cbl原癌基因的120-kDa蛋白产物，作为底物的受体偶联酪氨酸激酶的数量和形成复合物与SH 3和SH 2结构域的蛋白质，指出其在信号转导中的作用。基于秀丽隐杆线虫Cbl同源物SLI-1作为LET-23受体酪氨酸激酶的负调节剂的遗传证据，以及我们证明Cbl进化上保守的N-末端转化区（Cbl-N;残基1至357）具有与活化的ZAP-70酪氨酸激酶结合的磷酸酪氨酸结合（PTB）结构域，我们研究了致癌Cbl突变体可能通过去调节细胞酪氨酸激酶机制而激活促有丝分裂信号的可能性。在这里，我们表明，在NIH 3 T3成纤维细胞中，Cbl-N和其他两种转化型Cbl突变体（Cbl Y368 Delta和Cbl 366 -382 Delta或Cbl 70 Z）而非野生型Cbl的表达导致内源性酪氨酸激酶信号传导的增强。我们确定了血小板衍生生长因子受体α（PDGFR α）作为突变型Cbl诱导的失调的一个靶点。在突变型Cbl转染子中，PDGFR α被过度磷酸化，并与许多含SH 2结构域的蛋白质组成性复合。PDGFR α过度磷酸化和增强的突变Cbl转染的NIH 3 T3细胞的增殖在血清饥饿时显著降低，并且PDGF-AA取代了这些性状的维持，PDGF-AA刺激血清饥饿的Cbl转染子诱导转染的Cbl蛋白与PDGFR α的体内缔合。在体外，Cbl-N直接结合PDGF-AA刺激的细胞衍生的PDGFR α，但不结合未刺激的细胞衍生的PDGFR α，并且这种结合被对应于SLI-1中的功能丧失突变的点突变（G306 E）废除。Cbl-N/G306 E突变蛋白不能诱导NIH 3 T3细胞的增强生长和转化，也不能诱导PDGFR α的过度磷酸化。总之，这些研究结果确定了一种新的机制Cbl的生理功能和肿瘤发生，涉及其PTB结构域依赖的直接相互作用与细胞酪氨酸激酶。
Recent studies have demonstrated that Cbl, the 120-kDa protein product of the c-cbl proto-oncogene, serves as a substrate of a number of receptor-coupled tyrosine kinases and forms complexes with SH3 and SH2 domain-containing proteins, pointing to its role in signal transduction. Based on genetic evidence that the Caenorhabditis elegans Cbl homolog, SLI-1, functions as a negative regulator of the LET-23 receptor tyrosine kinase and our demonstration that Cbl's evolutionarily conserved N-terminal transforming region (Cbl-N; residues 1 to 357) harbors a phosphotyrosine binding (PTB) domain that binds to activated ZAP-70 tyrosine kinase, we examined the possibility that oncogenic Cbl mutants may activate mitogenic signaling by deregulating cellular tyrosine kinase machinery. Here, we show that expression of Cbl-N and two other transforming Cbl mutants (CblY368 Delta and Cbl366-382 Delta or Cbl70Z), but not wild-type Cbl, in NIH 3T3 fibroblasts leads to enhancement of endogenous tyrosine kinase signaling. We identified platelet-derived growth factor receptor alpha (PDGFR alpha) as one target of mutant Cbl-induced deregulation. In mutant Cbl transfectants, PDGFR alpha was hyperphosphorylated and constitutively complexed with a number of SH2 domain-containing proteins. PDGFR alpha hyperphosphorylation and enhanced proliferation of mutant Cbl-transfected NIH 3T3 cells were drastically reduced upon serum starvation, and PDGF-AA substituted for the maintenance of these traits, PDGF-AA stimulation of serum-starved Cbl transfectants induced the in vivo association of transfected Cbl proteins with PDGFR alpha. In vitro, Cbl-N directly bound to PDGFR alpha derived from PDGF-AA-stimulated cells but not to that from unstimulated cells, and this binding was abrogated by a point mutation (G306E) corresponding to a loss-of-function mutation in SLI-1. The Cbl-N/G306E mutant protein, which failed to induce enhanced growth and transformation of NIH 3T3 cells, also failed to induce hyperphosphorylation of PDGFR alpha. Altogether, these findings identify a novel mechanism of Cbl's physiological function and oncogenesis, involving its PTB domain-dependent direct interaction with cellular tyrosine kinases.