AbstractThe current study shows that a clonal derivative of the Jurkat cell line up‐regulates both the avidity and density of the α 6/β1 receptor in response to phorbol 12‐myristate 13‐acetate (PMA). This derivative attaches to fibronectin and, to a lesser degree, laminin constitutively. Adhesion and spreading are dramatically up‐regulated following treatment with PMA. The response on fibronectin peaks within 4 hours, is insensitive to cyclohexaminde, can be blocked by monoclonal antibodies (Mabs) to the β1 and α 5 subunits of the β1 family of integrins, and is not associated with increased expression of the α 5 or β1 epitopes at the cell surface. In contrast, the response on laminin is biphasic. The early phase parallels the response on fibronectin. The second phase peaks after 48–72 hours of treatment with PMA, is sensitive to cycloheximide, can be blocked by Mabs to the β1 and α 6 subunits, and is associated with increased expression of the α 6 epitope. Both the density independent and dependent responses to PMA in Jurkat cells are blocked by the protein kinase inhibitor staurosporine. The HSB‐2, CEM, Molt‐4, and HPB‐ALL T‐lymphoblastic cell lines also up‐regulate attachment to fibronectin and laminin following treatment with PMA. All four lines constitutively attach to fibronectin and show rapid up‐regulation of attachment following treatment with PMA. None of the lines attach to laminin prior to PMA treatment; however, specific adhesion developed after 4–120 hours of treatment. The most mature lines (Jurkat and HPB‐ALL) up‐regulated adhesion on laminin more rapidly than the less phenotypically mature lines (CEM, Molt‐4, and HSB‐2). In summary, clonal derivatives of the Jurkat cell line up‐regulated attachment to laminin through protein kinase dependent increases in α /β1 receptor avidity and density. In addition, the expression of functional receptors for laminin is linked to developmental maturity in a series of T‐l
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