ARGINYLATED CALRETICULIN: A NEW ISOSPECIES OF CALRETICULIN COMPONENT OF STRESS GRANULES

MARCOS A. CARPIO; MARÍA BELÉN DECCA; CHRISTOPHE BOSC; MAURICIO R. GALIANO; MARTA E. HALLAK

Rosario

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2006

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

The post-translational arginylation consists in the covalent union of an arginine into an acidic amino acid at the N-terminal position. Using mass spectrometry, we demonstrated in vitro the posttranslational incorporation of arginine into calreticulin (CRT). To further study arginylated-CRT we raised an antibody against the peptide RDPAIYFK, which contains an arginine followed by the first 7 N terminal aa of mature CRT. This antibody specifically recognizes CRT obtained from rat soluble fraction that was arginylated in vitro and also recognizes endogenous arginylated CRT from cells in culture, indicating that CRT arginylation takes place in living cells. We found that arginylation of CRT is Ca2+- regulated. In vitro and in cells in culture, the level of arginylated- CRT increased with the addition of a Ca2+ chelator, whereas a decreased arginine incorporation into CRT was found in the presence of Ca2+. The arginylated-CRT was observed in the cytosol, in contrast to the non arginylated CRT which is in the ER. Under stress conditions, arginylated-CRT was found associated to stress granules. These results suggest that CRT arginylation occurs in the cytosolic pool of mature CRT which is probably retro-translocated from the ER. [This work was supported in part by grants from the CONICET- FONCyt, SECYT UNC and from SECyT (Argentina)-ECOS (France)].