TipC and the chorea-acanthocytosis protein VPS13A regulate autophagy in <i>Dictyostelium</i> and human HeLa cells

Deficient autophagy causes a distinct phenotype in <i>Dictyostelium discoideum</i>, characterized by the formation of multitips at the mound stage. This led us to analyze autophagy in a number of multitipped mutants described previously (<i>tipA</i>⁻, <i>tipB</i>⁻, <i>tipC</i>⁻, and <i>tipD</i>⁻). We found a clear autophagic dysfunction in <i>tipC</i>⁻ and <i>tipD</i>⁻ while the others showed no defects. <i>tipD</i> codes for a homolog of Atg16, which confirms the role of this protein in <i>Dictyostelium</i> autophagy and validates our approach. The <i>tipC-</i>encoded protein is highly similar to human VPS13A (also known as Chorein), whose mutations cause the chorea-acanthocytosis syndrome. No member of the VPS13 protein family has been previously related to autophagy despite the presence of a region of similarity to Atg2 at the C terminus. This region also contains the conserved domain of unknown function DUF1162. Of interest, the expression of the TipC C-terminal coding sequence containing these 2 motifs largely complemented the mutant phenotype. <i>Dictyostelium</i> cells lacking TipC displayed a reduced number of autophagosomes visualized with the markers GFP-Atg18 and GFP-Atg8 and an impaired autophagic degradation as determined by a proteolytic cleavage assay. Downregulation of human <i>VPS13A</i> in HeLa cells by RNA interference confirmed the participation of the human protein in autophagy. VPS13A-depleted cells showed accumulation of autophagic markers and impaired autophagic flux.