Cytosolic phosphorylation of calnexin controls intracellular Ca2+ oscillations via an interaction with SERCA2b

H. Llewelyn Roderick, James D. Lechleiter, Patricia Camacho

Research output: Contribution to journalArticlepeer-review

177 Scopus citations

Abstract

Calreticulin (CRT) and calnexin (CLNX) are lectin chaperones that participate in protein folding in the endoplasmic reticulum (ER). CRT is a soluble ER lumenal protein, whereas CLNX is a transmembrane protein with a cytosolic domain that contains two consensus motifs for protein kinase (PK) C/proline-directed kinase (PDK) phosphorylation. Using confocal Ca2+ imaging in Xenopus oocytes, we report here that coexpression of CLNX with sarco endoplasmic reticulum calcium ATPase (SERCA) 2b results in inhibition of intracellular Ca2+ oscillations, suggesting a functional inhibition of the pump. By site-directed mutagenesis, we demonstrate that this interaction is regulated by a COOH-terminal serine residue (S562) in CLNX. Furthermore, inositol 1,4,5-trisphosphate-mediated Ca2+ release results in a dephosphorylation of this residue. We also demonstrate by coimmunoprecipitation that CLNX physically interacts with the COOH terminus of SERCA2b and that after dephosphorylation treatment, this interaction is significantly reduced. Together, our results suggest that CRT is uniquely regulated by ER lumenal conditions, whereas CLNX is, in addition, regulated by the phosphorylation status of its cytosolic domain. The S562 residue in CLNX acts as a molecular switch that regulates the interaction of the chaperone with SERCA2b, thereby affecting Ca2+ signaling and controlling Ca2+-sensitive chaperone functions in the ER.

Original languageEnglish (US)
Pages (from-to)1235-1247
Number of pages13
JournalJournal of Cell Biology
Volume149
Issue number6
DOIs
StatePublished - Jun 12 2000

Keywords

  • Ca ATPases
  • Ca signaling
  • Calnexin
  • ER lectin chaperones
  • Phosphorylation

ASJC Scopus subject areas

  • Cell Biology

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