Calcimycin kills mycobacteria by inducing autophagy through intracellular calcium in P2RX7 dependent pathway

Abstract

Calcium ionophores like calcimycin show in vitro antimicrobial activity against gram-positive bacteria and fungi but its effect on mycobacteria is not known. Present study was undertaken to understand the role of calcimycin that increases intracellular calcium level on intracellular mycobacteria in THP-1 cells. Firstly, MTT assay revealed that 0.4 μM of calcimycin is non-cytotoxic in phorbol myristate acetate (PMA) differentiated THP-1 cells till 72 h of treatment. Secondly, we found optimum upregulation of different autophagy markers like Beclin-1, Atg 7, Atg 3 and more conversion of LC3-II from LC3-I by calcimycin after 12 h of treatment through western blotting and confocal microscopy respectively. Increased autophagy in calcimycin treated cells led to decrease in intracellular M. smegmatis and M. bovis BCG viability and addition of 3-MA reversed this effect. Calcimycin binding with P2RX7 led to increase in intracellular calcium level that regulated the extracellular release of ATP. Blocking of either P2RX7 expression by KN-62 or reducing intracellular calcium levels by BAPTA-AM abrogated the antimycobacterial activity of calcimycin. We conclude that calcimycin exerts its antimycobacterial effect by regulating intracellular calcium-dependent ATP release that induces autophagy in a P2RX7 dependent manner.