title: Rac1-mediated Bcl-2 induction is critical in antigen-induced CD4 single-positive differentiation of a CD4+CD8+ immature thymocyte line.
abstract: Rac1, one of the Rho family small guanosine triphosphatases, has been shown to work as a "molecular switch" in various signal transduction pathways. To assess the function of Rac1 in the differentiation process of CD4 single-positive (CD4-SP) T cells from CD4CD8 double-positive (DP) cells, we used a DP cell line DPK, which can differentiate into CD4-SP cells upon TCR stimulation in vitro. DPK expressing dominant-negative (dn)Rac1 underwent massive apoptosis upon TCR stimulation and resulted in defective differentiation of CD4-SP cells. Conversely, overexpression of dnRac2 did not affect differentiation. TCR-dependent actin polymerization was inhibited, whereas early ERK activation was unaltered in dnRac1-expressing DPK. We found that TCR-dependent induction of Bcl-2 was suppressed greatly in dnRac1-expressing DPK, and this suppression was independent of actin rearrangement. Furthermore, introduction of exogenous Bcl-2 inhibited TCR-dependent induction of apoptosis and restored CD4-SP generation in dnRac1-expressing DPK without restoring TCR-induced actin polymerization. Collectively, these data indicate that Rac1 is critical in differentiation of CD4-SP from the DP cell line by preventing TCR-induced apoptosis via Bcl-2 up-regulation.
authors.affiliation: Department of Microbiology and Immunology, Yamaguchi University School of Medicine, Ube, Japan.
authors.forename: Hiroyo
authors.initials: H
authors.lastname: Oda
authors.forename: Harumi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Kouhei
authors.initials: K
authors.lastname: Sakai
authors.forename: Seiji
authors.initials: S
authors.lastname: Kitahara
authors.forename: Michael S
authors.initials: MS
authors.lastname: Patrick
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Azuma
authors.forename: Kazuro
authors.initials: K
authors.lastname: Sugi
authors.forename: Toshio
authors.initials: T
authors.lastname: Kitamura
authors.forename: Jonathan
authors.initials: J
authors.lastname: Kaye
authors.forename: Mutsunori
authors.initials: M
authors.lastname: Shirai
mesh_terms: D017209:Apoptosis / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002454:Cell Differentiation / Q000276:immunology; D002460:Cell Line; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; C107953:RAC1 protein, human; D011948:Receptors, Antigen, T-Cell; D020830:rac1 GTP-Binding Protein