GABA Type A receptors expressed in triple negative breast cancer cells mediate chloride ion flux

Triple negative breast cancer (TNBC) is known for its heterogeneous nature and aggressive onset, limited unresponsiveness to hormone therapies and immunotherapy as well as high likelihood of metastasis and recurrence. Since no targeted standard treatment options are available for TNBC, novel and effective therapeutic targets are urgently needed. Ion channels have emerged as possible novel therapeutic candidates for cancer therapy. We previously showed that GABA_A β3 subunit are expressed at higher levels in TNBC cell lines than non-tumorigenic MCF10A cells. GABA_A β3 subunit knockdown causes cell cycle arrest in TNBC cell lines via decreased cyclin D1 and increased p21 expression. However, it is not known if the upregulated GABA_AR express at the cell-surface in TNBC and mediate Cl^- flux. Cl^- ions are known to play a role in cell-cycle progression in other cancers such as gastric cancer. Here, using surface biotinylation and (N-(Ethoxycarbonylmethyl)-6-Methoxyquinolinium Bromide) MQAE-dye based fluorescence quenching, we show that upregulated GABA_AR are on the cell-surface in TNBC cell lines and mediate significantly higher chloride (Cl^-) flux as compared to non-tumorigenic MCF10A cells. Moreover, this GABA_AR mediated Cl^- flux can be modulated by pharmacological agents and is decreased in TNBC cells with GABA_A β3 subunit knockdown. Further, treatment of TNBC cells with bicuculline, a GABA_AR antagonist reduced cell viability in TNBC cells Overall, these results point to an unexplored role of GABA_AR mediated Cl^- flux in TNBC.