Comparison of the effects of tumour necrosis factor alpha stimulation and phorbol ester treatment on the immunocytochemical staining of intercellular adhesion molecule 1 in human renal carcinoma cell cultures.

Incubation of the human renal carcinoma cell line CaKi-1 with tumour necrosis factor alpha (TNF alpha) or the phorbol ester phorbol-12-myristate 13 acetate (PMA) strongly enhanced the immunocytochemical staining of the intercellular adhesion molecule ICAM-1, in a non-linear manner. Since PMA is capable of activating Ca2+/phospholipid-dependent protein kinase C (PKC), we investigated the role of this kinase during TNF alpha signal transduction. Calcium ionophore A23187 significantly enhanced PMA, but not TNF alpha-induced ICAM-1 staining. The PKC inhibitors H7, staurosporine and sphingosine abrogated the action of PMA, while TNF alpha was unaffected. Simultaneous incubation with TNF alpha and PMA resulted in maximal ICAM-1 staining significantly above values obtained when cultures were treated with either agent alone. Finally, chronic PMA treatment with subsequent TNF alpha stimulation enhanced ICAM-1 staining above values from cultures where TNF alpha was omitted. Our findings suggest that the immunocytochemical staining of ICAM-1 in CaKi-1 cells can be induced by TNF alpha through mainly PKC-independent mechanisms or by PMA through PKC-dependent mechanisms. The two agents may work synergistically in this respect.