OVEREXPRESSION OF BCL-2 IN KAPOSIS SARCOMA-DERIVED CELLS

The pathogenesis of Kaposi's sarcoma (KS), a tumor of probable vascula r origin, remains an enigma, It is still unclear whether KS is a true malignancy or whether it represents a reactive polyclonal process. Usi ng both an immunohistochemical and an immunoblot approach, we found th at cells derived from KS lesions express significant levels of Bcl-2, a protein known to prolong cellular viability and to antagonize apopto sis, Bcl-2 expression was found in AIDS-related KS-derived cells, as w ell as in cells derived from iatrogenic and sporadic KS, indicating th at Bcl-2 upregulation may be important in the pathogenesis of KS regar dless of its epidemiologic form, By contrast, fibroblasts and dermal m icrovascular endothelial, cells which are the probable vascular progen itors of KS cells, expressed low levels of Bcl-2, The expression of Bc l-2 in KS-derived cells was associated with a longterm survival in ser um-deprived conditions, a situation that has been shown to induce apop tosis in various cell types. Incubation of fibroblasts or of dermal mi crovascular endothelial cells with KS cell-free supernatants did not e nhance Bcl-2 expression, suggesting that Bcl-2 expression is not media ted by an agent released by KS cells, Analogously, KS supernatants fai led to promote the viability of fibroblasts and of dermal microvascula r endothelial cells cultured in serum-free conditions. Our findings su ggest that the spindle cells derived from KS have a survival advantage and may adequately represent the tumor cells of KS.