Macrophage migration inhibitory factor regulates mitochondrial dynamics and cell growth of human cancer cell lines through CD74–NF-κB signaling

Abstract

The indispensable role of macrophage migration inhibitory factor (MIF) in cancer cell proliferation is unambiguous; although which specific roles the cytokine plays to block apoptosis preserving cell growth is still obscure. Using different cancer cell lines (AGS, HepG2, HCT 116 and HeLa), here we report that silencing of MIF severely deregulates mitochondrial structural dynamics by shifting the balance towards excess fission besides inducing apoptosis with increasing sub-G0 cells. Furthermore, enhanced mitochondrial Bax translocation along with cytochrome c release, down-regulation of Bcl-xL and Bcl-2 as well as up-regulation of Bad, Bax and p53 indicate the activation of mitochondrial pathway of apoptosis upon MIF silencing. The data also indicate a concerted down-regulation of Opa1 and Mfn 1 along with a significant elevation of Drp1, cumulatively causing mitochondrial fragmentation upon MIF silencing. Upregulation of Drp1 has been found to be further coupled with fissogenic serine616 phosphorylation and serine637 dephosphorylation to ensure enhanced mitochondrial translocation. Interestingly, MIF silencing has been found to be associated with decreased NF-κB activation. In fact, NF-κB knockdown in turn increases mitochondrial fission and cell death. In addition, silencing of CD74, the cognate receptor of MIF, remarkably increases mitochondrial fragmentation besides preventing cell proliferation, inducing mitochondrial depolarization and increasing apoptotic cell death. Thus it indicates an active operation of a MIF-regulated CD74-NF-κB signaling axis for maintaining mitochondrial stability and cell growth. Collectively, we propose that MIF, through CD74, constitutively activates NF-κB to control mitochondrial dynamics and stability for promoting carcinogenesis via averting apoptosis.