Nuclear EGFRvIII‐STAT5b complex contributes to glioblastoma cell survival by direct activation of the Bcl‐XL promoter

Abstract

Aberrant EGFR signaling strongly promotes glioma malignancy and treatment resistance. The most prevalent mutation, ΔEGFR/EGFRvIII, is an in-frame deletion of the extracellular domain, which occurs in more than 25% of glioblastomas and enhances growth and survival of tumor cells. Paradoxically, the signaling of the potent oncogene ΔEGFR is of low intensity, raising the question of whether it exhibits preferential signaling to key downstream targets. We have observed levels of phosphorylation of STAT5 at position Y699 in cells expressing ΔEGFR that are similar or higher than in cells that overexpress EGFR and are acutely stimulated with EGF, prompting us to investigate the role of STAT5 activation in glioblastoma. Here, we show that in human glioblastoma samples, pSTAT5 levels correlated positively with EGFR expression and were associated with reduced survival. Interestingly, the activation of STAT5b downstream of ΔEGFR was dependent on SFKs, while the signal from acutely EGF-stimulated EGFR to STAT5b involved other kinases. Phosphorylated STAT5b and ΔEGFR associated in the nucleus, bound DNA and were found on promoters known to be regulated by STAT5 including that of the Aurora A gene. ΔEGFR cooperated with STAT5b to regulate the Bcl-XL promoter and knockdown of STAT5b suppressed anchorage independent growth, reduced the levels of Bcl-XL and sensitized glioblastoma cells to cisplatin. Together these results delineate a novel association of nuclear ΔEGFR with STAT5b, which promotes oncogenesis and treatment resistance in glioblastoma by direct regulation of anti-apoptotic gene, Bcl-XL.

Multiple receptor tyrosine kinases converge on microRNA-134 to control KRAS, STAT5B, and glioblastoma

“…27,51 It has been shown that nuclear EGFRvIII-STAT5B complexes contribute to GBM cell survival by direct activation of the Bcl-XL promoter. 52 However, a link between MET and STAT5B in GBM has not been established before. We show for the first time that STAT5B protein is regulated by MET via miR-134 and that STAT5B mediates the effects of MET and possibly also other RTKs in GBM.…”

Cucurbitacin-I inhibits Aurora kinase A, Aurora kinase B and survivin, induces defects in cell cycle progression and promotes ABT-737-induced cell death in a caspase-independent manner in malignant human glioma cells

“…This complex serves as a transcriptional co-activator for a series of tumor-promoting genes such as cyclin D1, iNOS, B-myb, Aurora kinase and Cox-2. 57,70 In this report we evaluated the effect of the JAK/STAT inhibitor, cucurbitacin on malignant human glioma cells in vitro. Application of cucurbitacin to glioma cell lines inhibited cell proliferation and induced cell-cycle arrest regardless of mutational status of p53, PTEN and EGFR.…”

“…56 Later, Latha et al demonstrated that EGFRviii cooperated with STAT5 to regulate the Bcl -xL promoter. 57 This prompted us to investigate the role of JAK/STAT inhibitor cucurbitacin-I and the Bcl -2/Bcl -xL antagonist ABT-737 in glioma cell lines. In this study, we report that cotreatment with cucurbitacin-I and ABT-737 induced G2/M arrest and apoptosis regardless of EGFR, PTEN, and TP53 mutation status in malignant human glioma cell lines.…”

Access to the Nucleus and Functional Association with c-Myc Is Required for the Full Oncogenic Potential of ΔEGFR/EGFRvIII

“…Nuclear localization for ⌬EGFR has been reported recently in the context of association with STAT5 (10) and STAT3 (8,9). These interactions were shown to be important for ⌬EGFR regulation of genes, including the Bcl-XL (10) and Cox2 gene (9). The functional role of the nuclear ⌬EGFR is currently unknown.…”

“…Recent work from several laboratories has indicated that EGFR can shuttle directly into the nucleus in normal proliferating and cancerous cells. The functions of nuclear EGFR include regulating gene transcription via physical interaction with transcription factors (3)(4)(5)(6)(7)(8)(9)(10) and DNA damage repair (11). Correlative studies suggest an association of high nuclear EGFR and poor clinical outcome in breast (12), oral (13,14), bladder (15), and ovarian cancer (12,16), allowing that nuclear EGFR may also be significant in the behavior of gliomas.…”