바이러스 감염시 미토콘드리아 E3 ubiquitin ligase 인 MARCH5의 새로운 생체 기능

Abstract

Mitochondria have a central role in preserving cellular homeostasis. Ubiquitin proteasome system (UPS) on the mitochondria is one of quality control systems that works as a first line barrier against aggregated or misfolded proteins. In this study, I investigated functional role of mitochondrial E3 ligase, MARCH5, against protein aggregated at the mitochondria membranes. First, the mitochondrial antiviral signaling (MAVS) protein forms aggregates that elicit robust type-I interferon induction on viral infection, but persistent MAVS signaling leads to host immunopathology; it remains unknown how these signaling aggregates are resolved. Here I identify the mitochondria resident E3 ligase, MARCH5, as a negative regulator of MAVS aggregates. March5+/- mice and MARCH5-deficient immune cells exhibited low viral replication and elevated type-I interferon responses to RNA viruses. MARCH5 bound MAVS only during viral stimulation when MAVS forms aggregates, and these interactions required the RING domain of MARCH5 and the CARD of MAVS. MARCH5, but not its RING mutant of MARCH5H43W, reduced the level of MAVS aggregates. MARCH5 transferred ubiquitin to Lys7 and Lys500 of MAVS and promoted its proteasome-mediated degradation. Second, the hepatitis B virus X (HBx) is non-structural protein encoded by hepatitis B virus (HBV) genome. Highly expressed HBx accumulates at the mitochondria and induces mitochondrial dysfunction that contributes to the pathogenesis of liver cancer. I found that MARCH5 was co-immunoprecipitated with HBx, which was subsequently ubiquitinated through interaction with N-terminal RING domain of MARCH5, whereas MARCH5H43W, which has no ligase activity failed to ubiquitinate HBx. In vitro and in vivo ubiquitination assays revealed that MARCH5 facilitated polyubiquitin chain formation at HBx protein and its proteasome-dependent degradation. Taken together, MARCH5 is a crucial mitochondria-resident regulator that plays a protective role against accumulation of aggregated MAVS and HBx.