A Novel Isoform of the Secretory Pathway Ca2+,Mn2+-ATPase, hSPCA2, Has Unusual Properties and Is Expressed in the Brain

Minghui Xiang,Deepti Mohamalawari,Rajini Rao

doi:10.1074/jbc.m413116200

Minghui Xiang, Deepti Mohamalawari + Show 1 more

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https://doi.org/10.1074/jbc.m413116200

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Abstract

Unlike lower eukaryotes, mammalian genomes have a second gene, ATP2C2, encoding a putative member of the family of secretory pathway Ca2+,Mn(2+)-ATPases, SPCA2. Human SPCA2 shares 64% amino acid identity with the protein defective in Hailey Hailey disease, hSPCA1. We show that human SPCA2 (hSPCA2) has a more limited tissue distribution than hSPCA1, with prominent protein expression in brain and testis. In primary neuronal cells, endogenous SPCA2 has a highly punctate distribution that overlaps with vesicles derived from the trans-Golgi network and is thus different from the compact perinuclear distribution of hSPCA1 seen in keratinocytes and nonpolarized cells. Heterologous expression in a yeast strain lacking endogenous Ca2+ pumps reveals further functional differences from hSPCA1. Although the Mn(2+)-specific phenotype of hSPCA2 is similar to that of hSPCA1, Ca2+ ions are transported with much poorer affinity, resulting in only weak complementation of Ca(2+)-specific yeast phenotypes. These observations suggest that SPCA2 may have a more specialized role in mammalian cells, possibly in cellular detoxification of Mn2+ ions, similar to that in yeast. We point to the close links between manganese neurotoxicity and Parkinsonism that would predict an important physiological role for SPCA2 in the brain.

Highlights

The secretory pathway Ca2ϩ-ATPases (SPCA(s))1 are a recently recognized family of ion pumps that supply the lumen of the Golgi with divalent cations requisite for protein sorting, processing, and quality control
The short C terminus of human SPCA2 (hSPCA2) has a dileucine motif that may be involved in adaptor-mediated sorting and a potential type III PDZ binding motif, PEDV, at the C terminus that may be important for localization and trafficking [23, 24]
The absence of homozygous ATP2C1 mutations in humans and the autosomal dominant mode of inheritance of Hailey Hailey disease both point to an apparent essential role for the SPCA in mammalian physiology

Summary

Introduction

The secretory pathway Ca2ϩ-ATPases (SPCA(s)) are a recently recognized family of ion pumps that supply the lumen of the Golgi with divalent cations requisite for protein sorting, processing, and quality control (reviewed in Refs. 1 and 2). The founding member of this family, Pmr (for plasma membrane ATPase-related) was first described in the yeast Saccharomyces cerevisiae [3, 4], and shortly thereafter, a closely related gene (50% protein identity) was cloned from rat [5]. Heterologous expression studies of C. elegans PMR1 and human SPCA1 in COS1 cells and in yeast have confirmed Mn2ϩ transport ability and a similar high affinity for Ca2ϩ in the range of 0.25 ␮M, suggesting that these are shared features of the SPCA family [12,13,14]. We report that the corrected clone encodes a functional SPCA pump that clearly differs from hSPCA1 in its ability to complement the phenotypes of a pmr null strain of yeast. Biochemical characterization of hSPCA2 in yeast and subcellular localization in primary hippocampal cells reveal novel properties that may contribute to a distinct physiological role

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