CALRETICULINA ARGINILADA ELUDE LA DEGRADACION PROTEOSOMAL POR MEDIO DE SU HOMODIMERIZACIÓN

GOITEA VICTOR E.; HALLAK, MARTA E.

La Falda

Congreso; XIX Jornadas Científicas; 2013

Sociedad de Biología de Córdoba

ARGINYLATED CALRETICULIN AVOIDS PROTEASOMAL DEGRADATION THROUGH SELF-DIMERIZATION Goitea V.E. and Hallak M.E. Centro de Investigaciones en Química Biológica de Córdoba CIQUIBIC-CONICET, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba. Córdoba - Argentina E-mail: vgoitea@fcq.unc.edu.ar Arginylation is a posttranslational modification that occurs at the N-terminal position of proteins and it is catalyzed by the enzyme ATE1. The addition of Arg could be involved in the N-end rule, as a primary destabilizing residue. Calreticulin (CRT) is a protein that retrotranslocates from the endoplasmic reticulum to the cytoplasm, where it is arginylated (R-CRT). We have shown that R-CRT has a greater degree of dimerization than CRT. Here we evaluate if R-CRT is degraded by the proteasome and how dimerization affects its stability. Cells incubated in the presence of the proteasome inhibitor MG132 show increased levels of R-CRT compared with control cells. Moreover, in the presence of MG132 and after stress induced by thapsigargin, R-CRT remains at high levels. While during the recovery period in the absence of MG132, R-CRT levels return to the values of control cells. In order to evaluate the effects of CRT dimerization on its degradation, we transfect CRT -/- cells with CRT-EGFP or C146A-CRT-EGFP (which is unable to dimerize). Cells expressing CRT-EGFP exhibit higher levels of R-CRT than cells transfected with C146A-CRT-EGFP. In addition, when these cells are incubated in the presence of MG132 show an accumulation of R-CRT in both cases. Our results indicate that R-CRT is susceptible to be degraded by the proteasome and that dimer formation protects the protein from proteasomal degradation. Supported by SECyT-UNC, CONICET, ANPCyT-PICT