Upregulation of the expression of Fas antigen and Fas ligand in a human submandibular gland ductal cell line by okadaic acid

Fas receptor is a member of a superfamily of receptors characterized by cys teine-rich motifs in the extracellular domain of the molecule. Binding of F as ligand to the receptor leads to receptor activation and the induction of intracellular signals that result in apoptotic cell death. In the present study, the expression of mRNA and proteins of Fas receptor and Fas ligand w ere examined in human submandibular gland ductal (HSG) cells treated with o kadaic acid by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblot analysis. Six hundred and eighty-two bp of the PCR product of F as receptor mRNA was detected in HSG cells and a protein with an estimated molecular weight of 58,000 was expressed in HSG cells. Treatment of HSG cel ls with an agonistic anti-Fas monoclonal antibody resulted in death of HSG cells, indicating that the functional Fas receptor protein is expressed in HSG cells. Fas receptor protein expression stimulated by okadaic acid was e levated in a dose- and time-dependent manner, with maximal expression at 20 nM and 48 h treatment. Fas ligand mRNA was also detected constitutively in HSG cells by RT-PCR. Okadaic acid stimulated the expression of Fas ligand protein in HSG cells in a time-dependent manner, while the expression of th e ligand was low in untreated HSG cells. The molecular weight of Fas ligand was estimated as 68,000. An antagonistic anti-Fas ligand monoclonal antibo dy prevented okadaic acid-induced death in HSG cells in a dose-dependent fa shion as determined by WST-1 assay. The results indicate that the expressio n of Fas receptor and ligand is regulated by protein phosphatase(s) sensiti ve to okadaic acid and is involved in okadaic acid-induced apoptosis in HSG cells, The results also suggest that the Fas receptor-ligand system might regulate apoptosis in HSG cells. (C) 2000 Elsevier Science Ltd. All rights reserved.