Department of Cancer Biology
Actins; Antigens, Surface; Carbazoles; Carcinoma, Squamous Cell; Cell Membrane; Cell Size; *Chemotaxis; Desmosomes; Enzyme Activation; Epidermal Growth Factor; Humans; Indoles; Integrin alpha6beta4; Integrins; Keratins; Laminin; Phosphorylation; Phosphoserine; Phosphotyrosine; Protein Kinase C; Pseudopodia; Receptor, Epidermal Growth Factor; Signal Transduction; Tumor Cells, Cultured
We explored the hypothesis that the chemotactic migration of carcinoma cells that assemble hemidesmosomes involves the activation of a signaling pathway that releases the alpha6beta4 integrin from these stable adhesion complexes and promotes its association with F-actin in cell protrusions enabling it to function in migration. Squamous carcinoma-derived A431 cells were used because they express alpha6beta4 and migrate in response to EGF stimulation. Using function-blocking antibodies, we show that the alpha6beta4 integrin participates in EGF-stimulated chemotaxis and is required for lamellae formation on laminin-1. At concentrations of EGF that stimulate A431 chemotaxis ( approximately 1 ng/ml), the alpha6beta4 integrin is mobilized from hemidesmosomes as evidenced by indirect immunofluorescence microscopy using mAbs specific for this integrin and hemidesmosomal components and its loss from a cytokeratin fraction obtained by detergent extraction. EGF stimulation also increased the formation of lamellipodia and membrane ruffles that contained alpha6beta4 in association with F-actin. Importantly, we demonstrate that this mobilization of alpha6beta4 from hemidesmosomes and its redistribution to cell protrusions occurs by a mechanism that involves activation of protein kinase C-alpha and that it is associated with the phosphorylation of the beta4 integrin subunit on serine residues. Thus, the chemotactic migration of A431 cells on laminin-1 requires not only the formation of F-actin-rich cell protrusions that mediate alpha6beta4-dependent cell movement but also the disruption of alpha6beta4-containing hemidesmosomes by protein kinase C.
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Citation: J Cell Biol. 1999 Sep 6;146(5):1147-60. Link to article on publisher's website