title: The effects of cytochalasins on lymphocytes. Identification of distinct cytochalasin-binding sites in relation to mitogenic response and hexose transport.
abstract: Cytochalasin B inhibits phytomitogen-induced human lymphocyte proliferation with a Ki of approximately 6 X 10(-6) M. Cytochalasins A, C, D, E, and H are also inhibitory with varying degrees of potency, whereas cytochalasin G and chaetoglobosins A, B, C, E, F, and J are not at concentrations as high as 15 microM. Cytochalasin B also competitively inhibits carrier-mediated equilibrium exchange of hexose (Ki of approximately 7 X 10(-7) M), but cytochalasin E is ineffective. Cytochalasin B binds reversibly to the lymphocyte at three distinct sites: L, M, and H. The ligand binding at L site shows the apparent dissociation constant (Kd) of 1 to 3 X 10(-6) M and total binding sites (Bt) of 6 to 8 X 10(7)/cell, represents approximately 85% of the total saturable binding, displays a broad specificity interacting with cytochalasins C, D, and E, is not displaceable by D-glucose, is located mostly in a cytosol fraction, and exists in intimate relation to cytoskeletal actin. M site shows a Kd of 2 to 4 X 10(-7) M and Bt of 5 to 8 X 10(6)/cell, represents about 8% of the total saturable binding, shows stringent specificity not being displaced by cytochalasins C, D, and E, is competitively displaced by D-glucose and phloretin, and is quantitatively recoverable in the plasma membrane fraction. The binding to H site shows a Kd of 0.5 to 1.0 X 10(-7) M and Bt of 4 to 5 X 10(6)/cell, representing approximately 7% of the total saturable binding, shows a broad specificity, is insensitive to D-glucose, and is membrane bound. It is proposed that L site is actin and is involved in the inhibition of lymphocyte mitogenesis, whereas M site is associated with the hexose transport carrier. Structure-activity relationships of cytochalasin effects are also discussed.
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D003571:Cytochalasin B / Q000494:pharmacology; D003572:Cytochalasins / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D008213:Lymphocyte Activation / Q000187:drug effects; D008214:Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D008757:Methylglucosides / Q000378:metabolism; D008934:Mitogens; D011485:Protein Binding; D013329:Structure-Activity Relationship
chemical_list: D003572:Cytochalasins; D008757:Methylglucosides; D008934:Mitogens; D003571:Cytochalasin B