title: Increased LFA-1-mediated homotypic cell adhesion is associated with the G1 growth arrest induced by rapamycin in a T cell lymphoma.
abstract: The immunosuppressive macrolide, rapamycin, impedes the G1 to S cell cycle progression in cytokine-stimulated normal lymphocytes and in certain autonomously proliferating cell lines. Here, we found that the rapamycin-induced growth arrest augments homotypic aggregation in the YAC-1 T cell lymphoma. The growth arrest and increased aggregation were both blocked by the rapamycin antagonist, L-685,818, which interacts with the intracellular binding proteins mediating rapamycin's biochemical action. Moreover, rapamycin-induced aggregation was not seen in YAC-1 cells mutants selected for resistance to the drug's antiproliferative effect. Although the inhibition of G1/S progression induced by serum deprivation also resulted in increased cellular aggregation, cell cycle blockade in late G1 by mimosine, early S phase by hydroxyurea, or G2/M by nocodazole all failed to do so. Furthermore, the aggregation induced by rapamycin was blocked by antibodies to the alpha (CD11a) or beta (CD18) subunits of the integrin, LFA-1, or to its ligands, ICAM-1 and ICAM-2, and did not occur in LFA-1-deficient YAC mutants. However, the surface expression of LFA-1, ICAM-1, or ICAM-2 was not augmented in cells aggregated by rapamycin. Finally, the serine/threonine protein phosphatase inhibitor, okadaic acid, was found to abrogate rapamycin-induced aggregation. Therefore, rapamycin's impairment of YAC-1 cell growth in G1 is accompanied by enhanced LFA-1-mediated homotypic cell adhesion that may reflect an increase of the integrin's avidity for its ligands and may involve protein phosphorylation/dephosphorylation events. This suggests the existence of a link between cell cycle progression and "inside-out" LFA-1 signaling, possibly regulated by rapamycin's biochemical targets.
authors.affiliation: Department of Immunology, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
authors.forename: F J
authors.initials: FJ
authors.lastname: Dumont
authors.forename: P
authors.initials: P
authors.lastname: Fischer
authors.forename: A
authors.initials: A
authors.lastname: Sirotina
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D018845:CD11 Antigens / Q000276:immunology / Q000502:physiology; D018821:CD18 Antigens / Q000276:immunology / Q000502:physiology; D002448:Cell Adhesion / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D016895:Culture Media, Serum-Free; D005434:Flow Cytometry; D016193:G1 Phase; D006918:Hydroxyurea / Q000494:pharmacology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology*; D016399:Lymphoma, T-Cell; D008898:Mimosine / Q000494:pharmacology; D015739:Nocodazole / Q000494:pharmacology; D011090:Polyenes / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D020123:Sirolimus; D016559:Tacrolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000906:Antibodies; D018845:CD11 Antigens; D018821:CD18 Antigens; D016895:Culture Media, Serum-Free; D007166:Immunosuppressive Agents; D016169:Lymphocyte Function-Associated Antigen-1; D011090:Polyenes; C076383:L 685818; D008898:Mimosine; D015739:Nocodazole; D020123:Sirolimus; D016559:Tacrolimus; D006918:Hydroxyurea