Regulation of thymocyte β-selection, development and positive selection by glycogen synthase kinase-3

Glycogen synthase kinase-3 (GSK-3) is a ubiquitously expressed serine/threonine kinase, that exists as two isoforms in mammals, GSK-3 and GSK-3{beta}, that are key downstream mediators of the phosphatidylinositol 3 kinase, Wnt, Notch and other pathways. Here, we report that simultaneous inactivation of both GSK-3 and GSK-3{beta} during early thymocyte ontogeny has profound effects on both {beta}-selection and positive selection, key checkpoints essential to producing functionally mature {beta} T cells. Conditional GSK-3/{beta} knockout animals (LckCre+ GSK-3{beta}fl/fl) possessed pre-double positive (pre-DP) thymocytes (CD4-CD8-CD117-CD25-) with compromised TCR{beta} chain expression along with elevated levels of {beta}-catenin and reduced Notch activity. {beta}-selection was impaired allowing pre-DP thymocytes to differentiate to DP thymocytes (CD4+CD8+) while bypassing strict requirements for productive TCR{beta} chain rearrangements and functional expression. Also impaired was the requisite pre-TCR and Notch-mediated expansion that normally precedes differentiation to the DP stage. Consequently, LckCre+ GSK-3{beta}fl/fl mice initially generated fewer DP thymocytes that expressed significantly reduced levels of mature TCR. The aberrant DP thymocytes expressed high levels of the pro-survival Bcl-2 family member Mcl-1, failed positive selection and accumulated as CD4hiCD8lo positive selection intermediates resulting in loss of both mature CD4 and CD8 lineages. LckCre+ GSK-3{beta}fl/fl mice succumbed to oligoclonal peripheral lymphomas with high penetrance. These data reveal essential roles for GSK-3 in several checkpoints of early T cell development.