ERp57 Modulates STAT3 Signaling from the Lumen of the Endoplasmic Reticulum

Helen Coe,Joanna Jung,Jody Groenendyk,Daniel Prins,Marek Michalak

doi:10.1074/jbc.m109.054015

Abstract

ERp57 is an endoplasmic reticulum (ER) resident thiol disulfide oxidoreductase. Using the gene trap technique, we created a ERp57-deficient mouse model. Targeted deletion of the Pdia3 gene, which encodes ERp57, in mice is embryonic lethal at embryonic day (E) 13.5. Beta-galactosidase reporter gene analysis revealed that ERp57 is expressed early on during blastocyst formation with the highest expression in the inner cell mass. In early stages of mouse embryonic development (E11.5) there is a relatively low level of expression of ERp57. As the embryos developed, ERp57 became highly expressed in both the brain and the lungs (E15.5 and E18.5). The absence of ERp57 has no impact on ER morphology; expression of ER-associated chaperones and folding enzymes, ER stress, or apoptosis. ERp57 has been reported to interact with STAT3 (signal transducer and activator of transcription)-DNA complexes. We show here that STAT3-dependent signaling is increased in the absence of ERp57 and this can be rescued by expression of ER-targeted ERp57 but not by cytoplasmic-targeted protein, indicating that ERp57 affects STAT3 signaling from the lumen of the ER. ERp57 effects on STAT3 signaling are enhanced by ER luminal complex formation between ERp57 and calreticulin. In conclusion, we show that ERp57 deficiency in mouse is embryonic lethal at E13.5 and ERp57-dependent modulation of STAT3 signaling may contribute to this phenotype.

Highlights

Ulation of Ca2ϩ homeostasis, phospholipid and steroid synthesis, and regulation of the response to cellular stress [1,2,3]
It is not clear how STAT3 activity is negatively regulated by endoplasmic reticulum (ER) resident ERp57, it has been reported that ERp57 may sequester the inactive and active STAT3 preventing its interaction with DNA and activation of STAT3-dependent genes [6, 12]
We showed that the ER, but not cytoplasmic, form of ERp57 is responsible for inhibition of STAT3 activity

Summary

Introduction

Ulation of Ca2ϩ homeostasis, phospholipid and steroid synthesis, and regulation of the response to cellular stress [1,2,3]. Lentiviral transduction techniques were used to generate ERp57Ϫ/Ϫ and wild-type fibroblast-derived cells lines stably expressing recombinant proteins ERp57 or no signal sequence ERp57 [25]. Some of the ERp57-deficient cells were transfected with expression vectors encoding full-length, ER-targeted ERp57, or cytoplasm-targeted ERp57 with no signal sequence and were designated ERp57Ϫ/Ϫ-ERp57ER or ERp57Ϫ/Ϫ-ERp57cyt, respectively.

Results

Conclusion