Calreticulin signals upstream of calcineurin and MEF2C in a critical Ca(2+)-dependent signaling cascade.
We uncovered a new pathway of interplay between calreticulin and myocyte-enhancer factor (MEF) 2C, a cardiac-specific transcription factor. We establish that calreticulin works upstream of calcineurin and MEF2C in a Ca(2+)-dependent signal transduction cascade that links the endoplasmic reticulum and the nucleus during cardiac development. In the absence of calreticulin, translocation of MEF2C to the nucleus is compromised. This defect is reversed by calreticulin itself or by a constitutively active form of calcineurin. Furthermore, we show that expression of the calreticulin gene itself is regulated by MEF2C in vitro and in vivo and that, in turn, increased expression of calreticulin affects MEF2C transcriptional activity. The present findings provide a clear molecular explanation for the embryonic lethality observed in calreticulin-deficient mice and emphasize the importance of calreticulin in the early stages of cardiac development. Our study illustrates the existence of a positive feedback mechanism that ensures an adequate supply of releasable Ca(2+) is maintained within the cell for activation of calcineurin and, subsequently, for proper functioning of MEF2C.
Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Jeffrey
J
Lynch
Lei
L
Guo
Pascal
P
Gelebart
Kaari
K
Chilibeck
Jian
J
Xu
Jeffery D
JD
Molkentin
Luis B
LB
Agellon
Marek
M
Michalak
D000818:Animals; D019703:Calcineurin / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D037282:Calreticulin / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005246:Feedback / Q000502:physiology; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D006321:Heart / Q000196:embryology; D006801:Humans; D026161:MADS Domain Proteins; D064326:MEF2 Transcription Factors; D051379:Mice; D032383:Myocytes, Cardiac / Q000378:metabolism; D018006:Myogenic Regulatory Factors / Q000235:genetics / Q000378:metabolism*; D041681:NIH 3T3 Cells; D015533:Transcriptional Activation / Q000502:physiology
D037282:Calreticulin; D026161:MADS Domain Proteins; D064326:MEF2 Transcription Factors; C578040:MEF2C protein, human; C578041:Mef2c protein, mouse; D018006:Myogenic Regulatory Factors; D019703:Calcineurin; D002118:Calcium