Modulates apoptotic signal transduction or effector structures within the mitochondrial matrix. Affect cytochrome C release from the mitochondria and caspase 3 activation, but not caspase 8 activation. Isoform 1 increases apoptosis triggered by both TNF and the DNA-damaging agent mytomycin C; in sharp contrast, isoform 2 suppresses apoptosis. Can modulate IFN-gamma-mediated transcriptional activity. Isoform 2 may play a role in neuromuscular junction development as an effector of the MUSK signaling pathway. Interacts with JAK2, HSPA9B and IFN-gammaR2 chain. Interacts with Ras GTPase-activating protein 1 (RASA1). Isoform 2 interacts with MUSK (via the cytoplasmic domain) (By similarity). Recruited to the postsynaptic cell membrane of the neuromuscular junction through interaction with MUSK. Widely expressed with highest levels in heart, liver, lung and skeletal muscles. Also expressed in keratinocytes. Modulation of apoptosis, i.e. proapoptotic activity of isoform 1 and antiapoptotic activity of isoform 2, is J domain-dependent. Tyrosine phosphorylated. Truncated N-terminus. Truncated N-terminus.