The C9orf72-SMCR8 complex suppresses primary ciliogenesis as a RAB8A GAP

Approximately half of the familial cases of amyotrophic lateral sclerosis (ALS) and frontal temporal dementia (FTD) are attributed to the abnormal GGGGCC repeat expansion within the first intron of C9orf72, potentializing C9orf72 and its product as the most promising target for ALS therapeutics. Nevertheless, the biological function of C9orf72 remains unclear. Previously, we reported that C9orf72 and its binding partner, SMCR8, form a GTPase-activating protein (GAP) complex, which is proposed to regulate membrane trafficking and autophagy. Hereby, we found that the C9orf72-SMCR8 complex negatively regulates primary ciliogenesis and hedgehog (HH) signaling. Furthermore, the biochemical analysis and cell biology experiments identified C9orf72 as the RAB8A binding subunit and SMCR8 as the GAP subunit within the complex. Further, we discussed the relationship among the C9orf72-SMCR8 complex, primary ciliogenesis, and autophagy.