Temozolomide resistance in glioblastoma cells occurs partly through epidermal growth factor receptor-mediated induction of connexin 43

J L Munoz,S H Ramkissoon,P Rameshwar,S J Greco,V Rodriguez-Cruz,K L Ligon

doi:10.1038/cddis.2014.111

Abstract

Glioblastoma Multiforme (GBM) is an aggressive adult primary brain tumor with poor prognosis. GBM patients develop resistance to the frontline chemotherapy, temozolomide (TMZ). As the connexins (Cx) have been shown to have a complex role in GBM, we investigated the role of Cx43 in TMZ resistance. Cx43 was increased in the TMZ-resistant low passage and cell lines. This correlated with the data in The Cancer Genome Atlas. Cx43 knockdown, reporter gene assays, chromatin immunoprecipitation assay, real-time PCR and western blots verified a role for Cx43 in TMZ resistance. This occurred by TMZ-resistant GBM cells being able to activate epidermal growth factor receptor (EGFR). In turn, EGFR activated the JNK-ERK1/2-AP-1 axis to induce Cx43. The increased Cx43 was functional as indicated by gap junctional intercellular communication among the resistant GBM cells. Cell therapy could be a potential method to deliver drugs, such as anti-EGF to tumor cells. Similar strategies could be used to reverse the expression of Cx43 to sensitize GBM cells to TMZ. The studies showed the potential for targeting EGF in immune therapy. These agents can be used in conjunction with stem cell therapy to treat GBM.

Highlights

A number of intracellular pathways have been described in the growth and survival of Glioblastoma Multiforme (GBM)
This study reported on increased expression of connexin 43 (Cx43) in TMZ resistance GBM cell lines and low-passage cells (Figures 1 and 2)
The chromatin immunoprecipitation (ChIP) assay combined with pharmacological inhibitors supported a role for AP-1 in Cx43 induction

Summary

Introduction

A number of intracellular pathways have been described in the growth and survival of GBM. These include the activation of epidermal growth factor receptor (EGFR) in GBM cells. EGFR dysfunction correlates with poor prognosis.[6,7] GBM patients with increased EGFR expression have enhanced activation of the EGFR variant, EGFRvIII.[8] The EGFR is a member of the Erb family of receptor tyrosine kinases. Chemoresistance of GBM cells can occur by intercellular communication through gap junction (GJIC).[11] GJIC is established by the interaction between two hemichannels on adjacent cell membranes.[12] The hemichannels are formed by members of the connexin (Cx) protein family. We show an increase in Cx43 in TMZ-resistant GBM cells that formed GJIC between the resistant cells.

Methods

Results

Conclusion