Posttraslational arginylation of calreticulin.

MARÍA BELÉN DECCA; MAURICIO R. GALIANO; CHRISTOPHE BOSC; DIDIER JOB; MARTA E. HALLAK

Newport Beach, CA

Congreso; 34th Meeting of the American Society for Neurochemistry; 2003

American Society for Neurochemistry

Arginine can be posttranslationally incorporated from arginyl-tRNA into the NH2-terminus of soluble acceptor proteins in a reaction catalyzed by arginyl-tRNA protein transferase. The addition of arginine seems to be involved in the N-end rule protein degradation. We previously identified several rat brain proteins, all containing an acidic aminoacid at the N-terminal position that are substrate of the arginylation. One of these is calreticulin (CRT). This protein mainly regarded as endoplasmic reticulum resident, is also associated with proteins in the cytosol, nucleus and extracellular compartments. In this work we show that CRT obtained from different cell lines and species can be posttranslationally arginylated. We studied the arginylation of CRT using an antibody that specifically recognizes the arginylated form of this protein (R-CRT). By Western blot analysis, this antibody recognizes a 60 kDa protein which has an electrophoretic mobility identical to CRT. In in vitro assays, exogenous bovine calreticulin becomes arginylated, and is recognized by the anti R-CRT antibody. As we described previously for the increased arginylation of proteins in animals or cells exposed to stress conditions, immunocytochemical studies with this antibody show that levels of R-CRT are also increased in NIH-3T3 cells submitted to the stress condition of serum deprivation. Since the enzymatic system is cytoplasmic and the substrate is mainly endoplasmic reticulum localized, we postulated that the substrate could be translocated to cytosol for arginylation and further degradation.