title: Role of the microfibrillar system in knob action of transformed cells.
abstract: Transformed cells often display knobs (or blebs) distributed over their surface throughout most of interphase. Scanning electron microscopy (SEM) and time-lapse cinematography on CHO-K1 cells reveal roughly spherical knobs of 0.5-4 micron in diameter distributed densely around the cell periphery but sparsely over the central, nuclear hillock and oscillating in and out of the membrane with a period of 15-60 sec. Cyclic AMP derivatives cause the phenomenon of reverse transformation, in which the cell is converted to a fibroblastic morphology with disappearance of the knobs. A model was proposed attributing knob formation to the disorganization of the jointly operating microtubular and microfilamentous structure of the normal fibroblast. Evidence for this model includes the following: 1) Either colcemid or cytochalasin B (CB) prevents the knob disappearance normally produced by cAMP, and can elicit similar knobs from smooth-surfaced cells; 2) knob removal by cAMP is specific, with little effect on microvilli and lamellipodia; 3) immunofluorescence with antiactin sera reveals condensed, amorphous masses directly beneath the membrane of CB-treated cells instead of smooth, parallel fibrous patterns of reverse-transformed cells or normal fibroblasts; 4) transmission electron microscopy (TEM) of sections show dense, elongated microfilament bundles and microtubules parallel to the long axis of the reverse-transformed CHO cell, but sparse, random microtubules throughout the transformed cell and an apparent disordered network of 6-nm microfilaments beneath the knobs; 5) cell membranes at the end of telophase, when the spindle disappears and cleavage is complete, display typical knob activity as expected by this picture.
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002453:Cell Cycle; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000648:ultrastructure*; D002471:Cell Transformation, Neoplastic; D006224:Cricetinae; D003412:Cricetulus; D003571:Cytochalasin B / Q000494:pharmacology; D003599:Cytoskeleton / Q000502:physiology*; D003703:Demecolcine / Q000494:pharmacology; D005260:Female; D008168:Lung; D008855:Microscopy, Electron, Scanning; D008870:Microtubules / Q000502:physiology*; D010053:Ovary
chemical_list: D003571:Cytochalasin B; D003994:Bucladesine; D003703:Demecolcine