The Makes Caterpillars Floppy (MCF)-like domain of Vibrio vulnificus induces mitochondrion-mediated apoptosis

The multifunctional-autoprocessing repeats-in-toxin (MARTX_Vv) toxin of Vibrio vulnificus plays a significant role in the pathogenesis of this bacterium through delivery of up to five effector domains to the host cells. Previous studies have established that the MARTX_Vv toxin is linked to V. vulnificus dependent induction of apoptosis, but the region of the large multifunction protein essential for this activity was not previously identified. Recently, we showed that the Makes Caterpillar Floppy-like MARTX effector domain (MCF_Vv) is an autoproteolytic cysteine protease that induces rounding of various cell types. In this study, we demonstrate that cell rounding induced by MCF_Vv is coupled to reduced metabolic rate and inhibition of cellular proliferation. Moreover, delivery of MCF_Vv into host cells either as a fusion to the N-terminal fragment of anthrax toxin lethal factor or when naturally delivered as a V. vulnificus MARTX toxin led to loss of mitochondrial membrane potential, release of cytochrome c, activation of Bax and Bak, and processing of caspases and poly-(ADP-ribose) polymerase (PARP-γ). These studies specifically link the MCF_Vv effector domain to induction of the intrinsic apoptosis pathway by V. vulnificus.