title: The arginylation-dependent association of calreticulin with stress granules is regulated by calcium.
abstract: Post-translational modifications of proteins are important for the regulation of cell functions; one of these modifications is post-translational arginylation. In the present study, we show that cytoplasmic CRT (calreticulin) is arginylated by ATE1 (arginyl-tRNA protein transferase). We also show that a pool of CRT undergoes retrotranslocation from the ER (endoplasmic reticulum) to the cytosol, because in CRT-knockout cells transfected with full-length CRT (that has the signal peptide), cytoplasmic CRT appears as a consequence of its expression and processing in the ER. After the cleavage of the signal peptide, an N-terminal arginylatable residue is revealed prior to retrotranslocation to the cytoplasm where arginylation takes place. SGs (stress granules) from ATE1-knockout cells do not contain CRT, indicating that CRT arginylation is required for its association to SGs. Furthermore, R-CRT (arginylated CRT) in the cytoplasm associates with SGs in cells treated with several stressors that lead to a reduction of intracellular Ca2+ levels. However, in the presence of stressors that do not affect Ca2+ levels, R-CRT is not recruited to these loci despite the fact that SGs are formed, demonstrating Ca2+-dependent R-CRT association to SGs. We conclude that post-translational arginylation of retrotranslocated CRT, together with the decrease in intracellular Ca2+, promotes the association of CRT to SGs.
authors.affiliation: Centro de Investigaciones en Química Biológica de Córdoba, CIQUIBIC, CONICET-Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende X5000HUA, Córdoba, Argentina.
authors.forename: Marcos A
authors.initials: MA
authors.lastname: Carpio
authors.forename: Cecilia
authors.initials: C
authors.lastname: López Sambrooks
authors.forename: Edith S
authors.initials: ES
authors.lastname: Durand
authors.forename: Marta E
authors.initials: ME
authors.lastname: Hallak
mesh_terms: D019881:Aminoacyltransferases / Q000502:physiology*; D000818:Animals; D001120:Arginine / Q000378:metabolism* / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D037282:Calreticulin / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D003594:Cytoplasmic Granules / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D041681:NIH 3T3 Cells; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D013312:Stress, Physiological
chemical_list: D037282:Calreticulin; D001120:Arginine; D019881:Aminoacyltransferases; C019727:arginyltransferase; D002118:Calcium