title: Overexpression of calreticulin modulates protein kinase B/Akt signaling to promote apoptosis during cardiac differentiation of cardiomyoblast H9c2 cells.
abstract: Calreticulin is a Ca(2+)-binding molecular chaperone of the lumen of the endoplasmic reticulum. Calreticulin has been shown to be essential for cardiac and neural development in mice, but the mechanism by which it functions in cell differentiation is not fully understood. To examine the role of calreticulin in cardiac differentiation, the calreticulin gene was introduced into rat cardiomyoblast H9c2 cells, and the effect of calreticulin overexpression on cardiac differentiation was examined. Upon culture in a differentiation medium containing fetal calf serum (1%) and retinoic acid (10 nm), cells transfected with the calreticulin gene were highly susceptible to apoptosis compared with controls. In the gene-transfected cells, protein kinase B/Akt signaling was significantly suppressed during differentiation. Furthermore, protein phosphatase 2A, a Ser/Thr protein phosphatase, was significantly up-regulated, implying suppression of Akt signaling due to dephosphorylation of Akt by the up-regulated protein phosphatase 2A via regulation of Ca(2+) homeostasis. Thus, overexpression of calreticulin promotes differentiation-dependent apoptosis in H9c2 cells by suppressing the Akt signaling pathway. These findings indicate a novel mechanism by which cytoplasmic Akt signaling is modulated to cause apoptosis by a resident protein of the endoplasmic reticulum, calreticulin.
authors.affiliation: Department of Biochemistry and Molecular Biology in Disease, Atomic Bomb Disease Institute, Nagasaki 852-8523, Japan.
authors.forename: Kan
authors.initials: K
authors.lastname: Kageyama
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Ihara
authors.forename: Shinji
authors.initials: S
authors.lastname: Goto
authors.forename: Yoshishige
authors.initials: Y
authors.lastname: Urata
authors.forename: Genji
authors.initials: G
authors.lastname: Toda
authors.forename: Katsusuke
authors.initials: K
authors.lastname: Yano
authors.forename: Takahito
authors.initials: T
authors.lastname: Kondo
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D015152:Blotting, Northern; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D037282:Calreticulin; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000378:metabolism; D015536:Down-Regulation; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005822:Genetic Vectors; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D007476:Ionophores / Q000494:pharmacology; D008387:Marine Toxins; D008856:Microscopy, Fluorescence; D009206:Myocardium / Q000166:cytology; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D012261:Ribonucleoproteins / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D007476:Ionophores; D008387:Marine Toxins; D010080:Oxazoles; D011518:Proto-Oncogene Proteins; D012261:Ribonucleoproteins; C059041:calyculin A; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D002118:Calcium; D000077191:Wortmannin