Circumventing chemoresistance is crucial for effectively treating
cancer including
glioblastoma, a lethal
brain cancer. The
gap junction protein connexin 43 (
Cx43) renders
glioblastoma resistant to
chemotherapy; however, targeting
Cx43 is difficult because mechanisms underlying Cx43-mediated chemoresistance remain elusive. Here we report that
Cx43, but not other
connexins, is highly expressed in a subpopulation of
glioblastoma and
Cx43 mRNA levels strongly correlate with poor prognosis and chemoresistance in this population, making
Cx43 the prime therapeutic target among all
connexins. Depleting
Cx43 or treating cells with αCT1-a
Cx43 peptide inhibitor that sensitizes
glioblastoma to the
chemotherapy temozolomide-inactivates phosphatidylinositol-3
kinase (PI3K), whereas overexpression of
Cx43 activates this signaling. Moreover, αCT1-induced chemo-sensitization is counteracted by a PI3K active mutant. Further research reveals that αCT1 inactivates PI3K without blocking the release of PI3K-activating molecules from
membrane channels and that
Cx43 selectively binds to the PI3K catalytic subunit β (PIK3CB, also called PI3Kβ or p110β), suggesting that
Cx43 activates PIK3CB/p110β independent of its channel functions. To explore the therapeutic potential of simultaneously targeting
Cx43 and PIK3CB/p110β, αCT1 is combined with
TGX-221 or
GSK2636771, two PIK3CB/p110β-selective inhibitors. These two different treatments synergistically inactivate PI3K and sensitize
glioblastoma cells to
temozolomide in vitro and in vivo. Our study has revealed novel mechanistic insights into
Cx43/PI3K-mediated
temozolomide resistance in
glioblastoma and demonstrated that targeting
Cx43 and PIK3CB/p110β together is an effective therapeutic approach for overcoming chemoresistance.