Anchorage dependence of mitogen-induced G1 to S transition in primary T lymphocytes.
Anchorage dependence defines the cellular requirement for integrin-mediated adhesion to substrate to initiate DNA replication in response to growth factors. In this study we investigated whether normal T cells, which spend extended periods in a nonadherent state, show similar requirements for cell cycle progression in response to TCR stimulation. Resting primary T lymphocytes were induced to enter the cell cycle by TCR triggering, and leukocyte integrins were either engaged using purified ICAM-1 or inhibited with function-blocking mAbs. Our data indicate that leukocyte integrins complement TCR-driven mitogenic signals not as a result of their direct clustering but, rather, via integrin-dependent organization of the actin cytoskeleton. Leukocyte integrin-dependent reorganization of the actin cytoskeleton cooperates with the TCR to effect mitogen-activated protein kinase activation, but also represents a required late (4-8 h poststimulation) component in the mitogenic response of normal T cells. Prolonged leukocyte integrin-dependent spreading, in the context of intercellular contact, is a requisite for the production of the mitogenic cytokine IL-2, which, in turn, is involved in the induction of D3 cyclin and is primarily responsible for the decrease in the cyclin-dependent kinase inhibitor p27kip, resulting in retinoblastoma protein inactivation and S phase entry. Thus, T lymphocytes represent a peculiar case of anchorage dependence, in which signals conveyed by integrins act sequentially with the activating stimulus to effect a sustained production of the essential mitogenic cytokine.
Geginat
J
J
Scientific Institute San Raffaele-DIBIT, University of Milan School of Medicine, Italy.
Bossi
G
G
Bender
J R
JR
Pardi
R
R
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002448:Cell Adhesion / Q000276:immunology; D002453:Cell Cycle / Q000276:immunology; D018797:Cell Cycle Proteins; D048429:Cell Size / Q000276:immunology; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015536:Down-Regulation / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D016193:G1 Phase / Q000276:immunology*; D005786:Gene Expression Regulation / Q000276:immunology; D016762:Genes, fos; D016758:Genes, jun; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D007399:Interphase / Q000276:immunology; D007700:Kinetics; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology; D008869:Microtubule-Associated Proteins / Q000502:physiology; D008934:Mitogens / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism / Q000502:physiology; D016196:S Phase / Q000276:immunology*; D013601:T-Lymphocytes / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D000911:Antibodies, Monoclonal; D018797:Cell Cycle Proteins; D007376:Interleukin-2; D016169:Lymphocyte Function-Associated Antigen-1; D008869:Microtubule-Associated Proteins; D008934:Mitogens; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases