Yeast model based study identified myosin and calcium-dependent calmodulin signalling as a potential target for drug intervention in chorea-acanthocytosis

Abstract

Chorea-acanthocytosis (ChAc) is a rare neurodegenerative disease associated with mutations in the human VPS13A gene. The mechanism of ChAc pathogenesis is unclear. A simple yeast model was used to investigate the function of Vps13. Vps13, like hVps13A, is involved in vesicular protein transport, actin cytoskeleton organisation and phospholipid metabolism. A new phenotype of the vps13Δ mutant, SDS-hypersensitivity, was used to screen a yeast genomic library for multicopy suppressors. A fragment of the MYO3 gene, encoding the N-terminal part of myosin, a protein involved in the actin cytoskeleton and in endocytosis, was isolated. Myo3-N protein contains a motor head domain and a linker. The linker contains IQ motifs that mediate the binding of calmodulin, a negative regulator. Amino acid substitutions that disrupt the interaction of Myo3-N with calmodulin resulted in the loss of vps13Δ suppression. Production of Myo3-N downregulated the activity of calcineurin, a protein phosphatase regulated by calmodulin, and alleviated some defects in early endocytosis events. Importantly, EGTA, which sequesters calcium and thus downregulates calmodulin and calcineurin, was a potent suppressor of vps13Δ. We propose that Myo3-N acts by sequestering calmodulin, downregulating calcineurin and activation of Myo3, which is involved in endocytosis and in Osh2/3 dependent endoplasmic reticulum-plasma membrane contact sites. These results show that defects associated with vps13Δ could be overcome and point to a functional connection between Vps13 and calcium signalling as a possible target for chemical intervention in ChAc. Yeast ChAc models may uncover the underlying pathological mechanisms, may also serve as a platform for drug testing.