CALCIUM LEVELS MODULATE POST-TRANSLATIONAL ARGINYLATION

CARPIO, MARCOS A; DECCA, MARÍA B; GALIANO, MAURICIO R; HALLAK, MARTA E

PINAMAR, BS. AS., ARGENTINA

Congreso; 20TH ANNUAL MEETING ? ARGENTINE SOCIETY FOR NEUROCHEMISTRY; 2005

SAN, SAIB, PABMB

Arginine can be posttranslationally incorporated by the enzyme arginyl-tRNA protein transferase into the NH2-terminus of soluble acceptor proteins. Among the arginylated proteins is calreticulina (CRT), a mayor intracellular calcium binding protein. Many cellular functions of CRT, such as chaperone and nuclear export activities are regulated by Ca⁺² whose binding alters the conformation of CRT. Taking this into consideration, we studied if the posttranslational arginylation of CRT is also regulated by Ca⁺².  In vitro we found that the incorporation of ¹⁴C-arg is inhibited by Ca⁺² whereas it is increased in the presence of the Ca⁺² chelator EGTA. This is a specific effect on CRT since the arginylation of the other protein substrates was insensitive to calcium or EGTA. To address if arginylation of CRT is also modulated by Ca⁺², we induced intracellular Ca⁺² depletion in cultured cells by treatment with a combination of SERCA pump-inhibitor Thapsigargin and the membrane-permeant Ca⁺² chelator Bapta-AM. We found that intracellular Ca⁺² depletion dramatically increased the amount of arginylated CRT (100 % respect to the cells cultured in the presence of Ca⁺²) as determined by immunocytochemistry assays. These results show that the posttranslational arginylation of CRT is regulated by Ca⁺² levels, suggesting that a conformational change of CRT may be required for this modification to occur.