Effect of Hailey-Hailey Disease Mutations on the Function of a New Variant of Human Secretory Pathway Ca2+/Mn2+-ATPase (hSPCA1)

Rebecca J Fairclough,Leonard Dode,Jo Vanoevelen,Jens Peter Andersen,Ludwig Missiaen,Luc Raeymaekers,Frank Wuytack,Alain Hovnanian

doi:10.1074/jbc.m300509200

Abstract

ATP2C1, encoding the human secretory pathway Ca2+/Mn2+ ATPase (hSPCA1), was recently identified as the defective gene in Hailey-Hailey Disease (HHD), an autosomal dominant skin disorder characterized by persistent blisters and erosions. To investigate the underlying cause of HHD, we have analyzed the changes in expression level and function of hSPCA1 caused by mutations found in HHD patients. Mutations were introduced into hSPCA1d, a novel splice variant expressed in keratinocytes, described here for the first time. Encoded by the full-length of optional exons 27 and 28, hSPCA1d was longer than previously identified splice variants. The protein competitively transported Ca2+ and Mn2+ with equally high affinity into the Golgi of COS-1 cells. Ca2+- and Mn2+-dependent phosphoenzyme intermediate formation in forward (ATP-fuelled) and reverse (Pi-fuelled) directions was also demonstrated. HHD mutant proteins L341P, C344Y, C411R, T570I, and G789R showed low levels of expression, despite normal levels of mRNA and correct targeting to the Golgi, suggesting instability or abnormal folding of the mutated hSPCA1 polypeptides. P201L had little effect on the enzymatic cycle, whereas I580V caused a block in the E1 approximately P --> E2-P conformational transition. D742Y and G309C were devoid of Ca2+- and Mn2+-dependent phosphoenzyme formation from ATP. The capacity to phosphorylate from Pi was retained in these mutants but with a loss of sensitivity to both Ca2+ and Mn2+ in D742Y and a preferential loss of sensitivity to Mn2+ in G309C. These results highlight the crucial role played by Asp-742 in the architecture of the hSPCA1 ion-binding site and reveal a role for Gly-309 in Mn2+ transport selectivity.

Highlights

ATP2C1, encoding the human secretory pathway Ca2؉/Mn2؉ ATPase, was recently identified as the defective gene in Hailey-Hailey Disease (HHD), an autosomal dominant skin disorder characterized by persistent blisters and erosions
Mutations were introduced into hSPCA1d, a novel splice variant expressed in keratinocytes, described here for the first time
This variant was identified following the rapid amplification of cDNA ends (RACE)-PCR analysis, performed on cDNA reverse-transcribed from isolated human keratinocyte total RNA

Summary

Introduction

ATP2C1, encoding the human secretory pathway Ca2؉/Mn2؉ ATPase (hSPCA1), was recently identified as the defective gene in Hailey-Hailey Disease (HHD), an autosomal dominant skin disorder characterized by persistent blisters and erosions. Cells: plasma membrane (PMCA), sarco(endo)plasmic reticulum (SERCA), and Golgi-associated secretory pathway (SPCA) Ca2ϩ transport ATPases. Studies of null strains defective in PMR1 illustrated a pleiotropic effect on Golgi function, including impaired proteolytic processing, incomplete glycosylation, and defective pre-, post-, and intra-Golgi translocation of secreted proteins (5) These defects resulted in defective cell wall morphogenesis, which is interestingly reminiscent of abnormal keratinocyte adhesion in HHD. In the reversible enzymatic cycle, the binding of Ca2ϩ from the cytosol to high affinity binding sites located in the transmembrane domains is closely associated with the binding of ATP to the cytosolic domain and the subsequent formation of a phosphoenzyme intermediate In this high energy E1ϳP state, the enzyme goes through an extensive series of conformational changes to move the ion(s) through the transmembrane pore. Overexpression of human SPCA1 in yeast and Chinese hamster ovary cells was restricted to the Golgi compartment and, was able to complement the PMR1 null mutation, as demonstrated by the ability to transport Ca2ϩ and Mn2ϩ in yeast (12)

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