Guanine nucleotide exchange factor C9orf72 (C9orf72)

C9orf72 is a DENN domain-containing guanine nucleotide exchange factor (GEF) that regulates endosomal trafficking, autophagy, and cellular stress responses[1][2]. The protein functions as a central hub in multiple interconnected pathways: it acts as a GEF for Rab GTPases to control vesicular transport, forms a tripartite complex with SMCR8 and WDR41 to regulate autophagic flux, and coordinates stress granule dynamics and mitochondrial oxidative phosphorylation[2]. Hexanucleotide repeat expansions (GGGGCC) in the C9orf72 gene cause the most common form of familial amyotrophic lateral sclerosis and frontotemporal dementia through two mechanisms: loss of C9orf72 protein function (haploinsufficiency), which impairs autophagy and neuronal homeostasis, and gain of function from pathogenic RNA transcripts that sequester RNA-binding proteins in nuclear foci and generate toxic dipeptide repeat proteins[2][3]. Therapeutic strategies under investigation include antisense oligonucleotides targeting expanded repeat transcripts and approaches to restore C9orf72 protein-mediated autophagy[4].

Other names

C9orf72–SMCR8–WDR41 complex subunitDENN domain-containing protein C9orf72Chromosome 9 open reading frame 72C9-long (481-amino acid isoform)C9-short (222-amino acid isoform)

C9orf72 acts as a guanine nucleotide exchange factor (GEF) that promotes the conversion of inactive Rab GTPases (bound to GDP) to their active form (bound to GTP). The protein interacts with multiple Rab GTPases (Rab1, Rab5, Rab7, Rab11, Rab8a, Rab39b) to regulate their membrane recruitment and activation. C9orf72 also forms a tripartite complex with SMCR8 and WDR41 proteins that may function as a GTPase-activating protein (GAP) rather than a GEF. The protein coordinates cellular homeostasis through regulation of autophagy initiation (via interaction with the ULK1 complex), endosomal dynamics, and lysosomal biogenesis.