Mechanism of immune escape of human osteosarcoma cells through abnormal expressions of Fas and Fas ligand.

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Osteosarcoma cells frequently metastasize to the lungs. Metastatic process is composed of several different steps. Of them, escape from the immune surveilance system is one of the essential ability for osteosarcoma cells to obtain. Recent studies have reported that some carcinoma cells could escape from cytotoxic T-lymphocytes through loss of function of Fas receptor and might counter-attack them through gain of function of Fas ligand (Fas L). We investigated status and function of Fas and Fas L in human osteosarcomas to clarify the molecular mechanism of immune escape working in human osteosarcoma.1. Expressions of Fas and Fas L were demonstrated in established three human osteosarcoma cell lines (HOS, OST and Saos2) and three osteosarcma tissues both at message ad protein levels using RT-PCR and Western blot. No structural abnormality was detected by direct sequencing.2. Osteosarcoma tissues showed Fas of both membrane-bounded and soluble-form. Soluble Fas was a predominant form of F … More as produced in established osteosarcoma cell lines and only OST expressed not only soluble but membrane-bounded form, that was confirmed by immunofluorescent study. Immunohistochemical studies demonstrated expression of Fas in 17 of 22 osteosarcomas. Eleven osteosarcomas (65%) were membrane-type and 6 (35%) in the cytoplasm.3. Fas ligand expressed in both established osteosarcoma cells and tissues was membrane-bounded and no soluble Fas L was detected at all. Immunohistochemistry disclosed overexpression of Fas L in 17 (85%) of 20 cases. No significant correlation was detected between the expression of Fas L and clinicopatholgical parameters including stage, chemosensitivity and prognosis. Status of Fas L expression was not correlated to number of apoptosis of cytotoxic T-lymphocytes infiltrated in the tumor tissues demonstrated by TUNEL-CD8 staining.4. Function of Fas L expressed in osteosarcoma tissues and established osteosarcoma cell lines was demonstrated by the osbervation of apoptosis-induction in Fas-sensitive Jurkat cells which were incuvated on the frozen sections of osteosarcoma tissues or on monolayer of established osteosarcoma cell lines. The apoptosis was significantly inhibited by the incubation with neutralizing anti-Fas L antibody (NOK1), indicating that the apoptosis occurred via Fas/Fas L passway.5. Adriamycin-induced cardiaomyopathy was apoptotic mechanism via overexpession of Fas on the myocardium.These results showed that status of Fas and Fas L might reflect imprtant phenomena in human osteosarcoma and that osteosarcoma cells could escape from immune surveilance through loss of Fas and gain of FasL.Modulation of the Fas and Fas L expressions may be one of new therapeutic strategies against osteosarcomas. Less