Deficiency of ATP2C1, a Golgi Ion Pump, Induces Secretory Pathway Defects in Endoplasmic Reticulum (ER)-associated Degradation and Sensitivity to ER Stress

Jose Ramos-Castañeda,Young-Nam Park,Ming Liu,Karin Hauser,Hans Rudolph,Gary E Shull,Marcel F Jonkman,Kazutoshi Mori,Shigaku Ikeda,Hideoki Ogawa,Peter Arvan

doi:10.1074/jbc.m413243200

Abstract

Relatively few clues have been uncovered to elucidate the cell biological role(s) of mammalian ATP2C1 encoding an inwardly directed secretory pathway Ca2+/Mn2+ pump that is ubiquitously expressed. Deficiency of ATP2C1 results in a human disease (Hailey-Hailey), which primarily affects keratinocytes. ATP2C1-encoded protein is detected in the Golgi complex in a calcium-dependent manner. A small interfering RNA causes knockdown of ATP2C1 expression, resulting in defects in both post-translational processing of wild-type thyroglobulin (a secretory glycoprotein) as well as endoplasmic reticulum-associated protein degradation of mutant thyroglobulin, whereas degradation of a nonglycosylated misfolded secretory protein substrate appears unaffected. Knockdown of ATP2C1 is not associated with elevated steady state levels of ER chaperone proteins, nor does it block cellular activation of either the PERK, ATF6, or Ire1/XBP1 portions of the ER stress response. However, deficiency of ATP2C1 renders cells hypersensitive to ER stress. These data point to the important contributions of the Golgi-localized ATP2C1 protein in homeostatic maintenance throughout the secretory pathway.

Highlights

Few clues have been uncovered to elucidate the cell biological role(s) of mammalian ATP2C1 encoding an inwardly directed secretory pathway Ca2؉/Mn2؉ pump that is ubiquitously expressed
Effects of ATP2C1 on ER-associated degradation (ERAD), ER Stress Response, and ER Stress-induced Cell Toxicity—We have previously shown that the cog thyroglobulin mutation encodes a mutant glycoprotein that serves as a substrate for ERAD via the ubiquitin-proteasome system [26]
Despite the fact that the Hailey-Hailey disease phenotype is restricted to the skin of heterozygous individuals, no higher eukaryotic models have been identified to date in which both functional alleles of ATP2C1 are lacking, suggesting the possibility that homozygotes may suffer from a more general phenotype, which may be lethal

Summary

Introduction

Few clues have been uncovered to elucidate the cell biological role(s) of mammalian ATP2C1 encoding an inwardly directed secretory pathway Ca2؉/Mn2؉ pump that is ubiquitously expressed. Using siRNA-mediated knockdown of ATP2C1, we show that such cells exhibit defects in glycan processing of wild-type thyroglobulin (a secretory glycoprotein), ERAD of mutant thyroglobulin, and hypersensitivity to ER stress.

Results

Conclusion