Inositol-requiring enzyme 1 involved in regulating hemocyte apoptosis upon heat stress in Patinopecten yessoensis

The inositol-requiring enzyme 1 (IRE1), one of the primary endoplasmic reticulum (ER) transmembrane receptor proteins, is involved in regulating unfolded protein response (UPR) signaling pathway and plays an import role in maintaining cell homeostasis. In the present study, an IRE1 homologue was identified from Patinopecten yessoensis (designated as PyIRE1). The cDNA of PyIRE1 was of 3314 bp with a 2646 bp open reading frame (ORF) of IRE1 encoding a polypeptide of 881 amino acids. There was a signal peptide, four pyrrolo-quinoline quinine (PPQ) domains, a transmembrane helix region, a Serine/Threonine protein kinases domain (S_TKc) and a protein kinases or N-glycanases containing protein domain (PUG) in the deduced amino acid sequence of PyIRE1. The PyIRE1 mRNA was constitutively expressed in all the tested tissues, with the highest expression level in gills. PyIRE1 protein was mainly located in the ER of P. yessoensis hemocytes. The expression profiles of PyIRE1, glucose-regulated protein 94 (designated as PyGRP94) and glucose-regulated protein 78 (designated as PyGRP78) were determined by SYBR Green qRT-PCR after heat shock treatment. The mRNA expression levels of all these three genes were significantly up-regulated and reached their peak values at 2 h (3.97-fold, p < 0.05), 8 h (19.67-fold, p < 0.05) and 4 h (27.37-fold, p < 0.05) in hemocytes, 2 h (3.55-fold, p < 0.05), 12 h (8.58fold, p < 0.05) and 8 h (35.31-fold, p < 0.05) in gills after heat shock treatment, respectively. After the injection with PyIRE1 dsRNA, the mRNA expression of pro-apoptotic B-cell lymphoma-2 (Bcl-2) family member PyBax and the activity of caspase-3 significantly decreased in comparison with the control group (p < 0.05) after heat shock treatment. These results collectively suggested that PyIRE1, as an ER stress sensor, was potentially involved in the response upon heat stress by regulating the expression of PyBax and apoptosis of hemocytes in P. yessoensis.