Similar Ca2+-signaling properties in keratinocytes and in COS-1 cells overexpressing the secretory-pathway Ca2+-ATPase SPCA1

Abstract

Mutations in the ubiquitously expressed secretory-pathway Ca2+-ATPase (SPCA1) Ca2+ pump result in Hailey–Hailey disease, which almost exclusively affects the epidermal part of the skin. We have studied Ca2+ signaling in human keratinocytes by measuring the free Ca2+ concentration in the cytoplasm and in the lumen of both the Golgi apparatus and the endoplasmic reticulum. These signals were compared with those recorded in SPCA1-overexpressing and control COS-1 cells. Both the sarco(endo)plasmic-reticulum Ca2+-ATPase (SERCA) and SPCA1 can mediate Ca2+ uptake into the Golgi stacks. Our results indicate that keratinocytes mainly used the SPCA1 Ca2+ pump to load the Golgi complex with Ca2+ whereas the SERCA Ca2+ pump was mainly used in control COS-1 cells. Cytosolic Ca2+ signals in keratinocytes induced by extracellular ATP or capacitative Ca2+ entry were characterized by an unusually long latency reflecting extra Ca2+ buffering by an SPCA1-containing Ca2+ store, similarly as in SPCA1-overexpressing COS-1 cells. Removal of extracellular Ca2+ elicited spontaneous cytosolic Ca2+ transients in keratinocytes, similarly as in SPCA1-overexpressing COS-1 cells. With respect to Ca2+ signaling keratinocytes and SPCA1-overexpressing COS-1 cells therefore behaved similarly but differed from control COS-1 cells. The relatively large contribution of the SPCA1 pumps for loading the Golgi stores with Ca2+ in keratinocytes may, at least partially, explain why mutations in the SPCA1 gene preferentially affect the skin in Hailey–Hailey patients.