Insulin-Regulated Actin Dynamics is Disrupted in a Human Keratinocyte Model of Hailey Hailey Disease

Hailey Hailey Disease (HHD) is an autosomal dominant cutaneous disorder caused by mutations in ATP2C1, the gene encoding the Golgi/secretory pathway Ca²⁺-ATPase SPCA1. Characterized by suprabasal acantholysis and intertriginous blistering of the skin, HHD treatment focuses on managing symptoms as there is no cure. Challenges to targeted therapy are due to the lack of facile and reliable models, both human and rodent, for mechanistic studies. Here we validate and characterize CRISPR/Cas9 mediated single and bi-allelic ATP2C1 knockouts in immortalized human hTERT keratinocytes. Whereas SPCA1 expression, Golgi morphology and Golgi Ca²⁺ accumulation were proportionately affected in heterozygous and homozygous ATP2C1 null mutants as expected, both single and double allelic mutants showed near complete loss of cadherins associated with desmosomal and adherens junctions. HHD is characterized by poor wound healing and impaired keratinocyte migration. We show that SPCA1 is required for dynamic reorganization of actin cytoskeleton in keratinocyte spreading. We identified an insulin activated PI3K-AKT-Rac1 signaling pathway required for lamellipodia formation and keratinocyte spreading, defective in SPCA1 mutants. Transgenic expression of hSPCA1 or treatment with CDN1163, a small molecule Ca²⁺-ATPase agonist, restored defective phenotypes in the HHD model, paving the way for future therapeutic approaches to treat this disorder.