Li L, Chakraborty S, Yang C-R, Hatanpaa K J, Cipher D J, Puliyappadamba V T, Rehman A, Jiwani A J, Mickey B, Madden C, Raisanen J, Burma S, Saha D, Wang Z, Pingle S C, Kesari S, Boothman D A, Habib A A
Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Simmons Comprehensive Cancer Center, Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Oncogene. 2014 Aug 14;33(33):4253-64. doi: 10.1038/onc.2013.400. Epub 2013 Sep 30.
EGFRvIII is a key oncogene in glioblastoma (GBM). EGFRvIII results from an in-frame deletion in the extracellular domain of EGFR, does not bind ligand and is thought to be constitutively active. Although EGFRvIII dimerization is known to activate EGFRvIII, the factors that drive EGFRvIII dimerization and activation are not well understood. Here we present a new model of EGFRvIII activation and propose that oncogenic activation of EGFRvIII in glioma cells is driven by co-expressed activated EGFR wild type (EGFRwt). Increasing EGFRwt leads to a striking increase in EGFRvIII tyrosine phosphorylation and activation while silencing EGFRwt inhibits EGFRvIII activation. Both the dimerization arm and the kinase activity of EGFRwt are required for EGFRvIII activation. EGFRwt activates EGFRvIII by facilitating EGFRvIII dimerization. We have previously identified HB-EGF, a ligand for EGFRwt, as a gene induced specifically by EGFRvIII. In this study, we show that HB-EGF is induced by EGFRvIII only when EGFRwt is present. Remarkably, altering HB-EGF recapitulates the effect of EGFRwt on EGFRvIII activation. Thus, increasing HB-EGF leads to a striking increase in EGFRvIII tyrosine phosphorylation while silencing HB-EGF attenuates EGFRvIII phosphorylation, suggesting that an EGFRvIII-HB-EGF-EGFRwt feed-forward loop regulates EGFRvIII activation. Silencing EGFRwt or HB-EGF leads to a striking inhibition of EGFRvIII-induced tumorigenicity, while increasing EGFRwt or HB-EGF levels resulted in accelerated EGFRvIII-mediated oncogenicity in an orthotopic mouse model. Furthermore, we demonstrate the existence of this loop in human GBM. Thus, our data demonstrate that oncogenic activation of EGFRvIII in GBM is likely maintained by a continuous EGFRwt-EGFRvIII-HB-EGF loop, potentially an attractive target for therapeutic intervention.
表皮生长因子受体III型变异体（EGFRvIII）是胶质母细胞瘤（GBM）中的一种关键致癌基因。EGFRvIII是由表皮生长因子受体（EGFR）胞外结构域的框内缺失产生的，不结合配体，被认为具有组成性活性。虽然已知EGFRvIII二聚化可激活EGFRvIII，但驱动EGFRvIII二聚化和激活的因素尚不清楚。在此，我们提出了一种新的EGFRvIII激活模型，并认为胶质瘤细胞中EGFRvIII的致癌激活是由共表达的活化型EGFR野生型（EGFRwt）驱动的。增加EGFRwt会导致EGFRvIII酪氨酸磷酸化和激活显著增加，而沉默EGFRwt则会抑制EGFRvIII激活。EGFRwt的二聚化臂和激酶活性都是EGFRvIII激活所必需的。EGFRwt通过促进EGFRvIII二聚化来激活EGFRvIII。我们之前已鉴定出EGFRwt的一种配体——肝素结合表皮生长因子（HB-EGF），它是一种由EGFRvIII特异性诱导的基因。在本研究中，我们发现只有当EGFRwt存在时，HB-EGF才会被EGFRvIII诱导。值得注意的是，改变HB-EGF可重现EGFRwt对EGFRvIII激活的影响。因此，增加HB-EGF会导致EGFRvIII酪氨酸磷酸化显著增加，而沉默HB-EGF则会减弱EGFRvIII磷酸化，这表明EGFRvIII-HB-EGF-EGFRwt前馈环调节EGFRvIII激活。沉默EGFRwt或HB-EGF会导致EGFRvIII诱导的肿瘤发生受到显著抑制，而在原位小鼠模型中增加EGFRwt或HB-EGF水平则会导致EGFRvIII介导致癌作用加速。此外，我们在人GBM中证实了这种环的存在。因此，我们的数据表明GBM中EGFRvIII的致癌激活可能由持续的EGFRwt-EGFRvIII-HB-EGF环维持，这可能是一个有吸引力的治疗干预靶点。
