The avian transcription factor c-Rel is induced and translocates into the nucleus of thymocytes undergoing apoptosis

This study investigates the involvement of the avian transcription factor c-Rel in thymocyte apoptosis occurring either in vivo or in organotypic culture. In vivo, only a few cortical thymocytes express the c-Rel protein. Their number, localization and morphology resemble that of apoptotic cells evidenced by TUNEL staining. In organotypic culture, the expression of c-Rel is induced in medullary thymocytes as apoptosis is triggered. This induction would be posttranscriptional since no increase in the c-rel gene expression is detected. Moreover, c-Rel translocates into the nucleus of medullary thymocytes during the time course of apoptosis. This translocation is preceded by a decrease in ikba expression, the gene which encodes the avian homologue of I kappa B alpha. Altogether these results suggest that the protooncogene c-rel could take an active part in apoptosis of cortical thymocytes occurring in vivo during T-cell selection as well as in experimentally-induced apoptosis of medullary thymocytes.