Mitochondrial nicotinic acetylcholine receptors form complexes with Bax upon apoptosis induction
Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission in muscles and autonomic ganglia and regulate cytokine and neurotransmitter release in the brain and nonexcitable cells. The nAChRs expressed in the outer membrane of mitochondria control the early events of mitochondria-driven apoptosis like cytochrome c release by affecting intramitochondrial kinase pathways. However, the mechanisms through which nAChRs influence mitochondrial permeability remain obscure. Previously we demonstrated that mitochondrial nAChRs interact with voltage-dependent anion channels (VDAC) involved in forming the pore in mitochondria membrane. Here we put an aim to explore the connection of nAChRs to pro-apoptotic protein Bax and its changes in the course of apoptosis induction. By using molecular modeling in silico, it was shown that both Bax and VDAC bind within the 4th transmembrane portion of nAChR subunits. Experimentally, 7 nAChR-Bax and 7 nAChR-VDAC complexes were identified by sandwich ELISA in mitochondria isolated from astrocytoma U373 cells. Stimulating apoptosis of U373 cells by 1M H2O2 disrupted 7-VDAC complexes and favored formation of 7-Bax complexes. 7-selective agonist PNU282987 and type 2 positive allosteric modulator PNU120596 disrupted 7-Bax and returned 7 nAChR to complex with VDAC. It is concluded that mitochondrial nAChRs regulate apoptosis-induced mitochondrial channel formation by modulating the interplay of apoptosis-related proteins in mitochondria outer membrane.