Résumé :
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?-Dystroglycan (?-DG) is a transmembrane protein that links the extracellular matrix with the cytoskeleton. This protein is a Dystrophin-associated protein (DAP) that has an important role in cell signaling, and cytoplasm and nuclear organization (Fuentes-Mera, 2006). Recently, it has been reported that ?-DG undergoes tyrosine phosphorylation in a cell adhesion-dependent manner. However, phosphorylated ?-DG has not been detected in nuclei. In the present work, we studied the sub-nuclear localization of ?-DG and its phosphorylated status at nuclei from cerebral cortex of rat. We found that the nuclear pattern of ?-DG was different that in rat brain extract. The canonical ?-DG band of 47kDa was detected in rat brain extract with anti-?-DG antibodies (NCL-43DG, G5 and JAF), but was undetectable with anti-phospho Y892 antibody that recognizes the ?-DG C-terminal phosphorylated tyrosine 892 residue, indicating that it is not phosphorylated. The ?-DG band was almost undetected in nuclei, nuclear matrix and nuclear membrane fractions. However, some protein bands with upward or downward mobility shifts (250, 190, 115, 65, 44, 41, 38 and 35 kDa) were detected in nuclear extract and nuclear matrix fraction. These bands were more immunoreactive in nuclear that in rat brain extracts. We hipothethized, that these nuclear proteins are post-transductional modified ?-DG. With the anti-phospho Y892 antibody, we confirmed that ?-DG bands expressed in nuclei are phosphorylated. The phospho-?-DG bands of upward mobility shifts may be poly-glycosilated isoforms. For the first time, we have demonstrated the enriched expression of phospho-?-DG isoforms at nuclei from cerebral cortex and nuclear matrix fraction. These results give new insights about the possible functions of phospho-?-DGs in the nuclear architecture and the anchorage of signaling proteins at nuclei.
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