KAPOSIS-SARCOMA TUMOR-CELLS PREFERENTIALLY EXPRESS BCL-X(L)

Several recently identified proteins such as Bcl-2 and Bcl-x have been found to regulate programmed cell death (ie, apoptosis). In this repo rt, we examined the levels of expression of proteins that can either p revent apoptosis (ie, Bcl-2 or he long form of Bcl-x, designated Bcl-x (L)) or promote apoptosis (ie, Bax or the short form of Bcl-x, designa ted Bcl-x(s)) in proliferating benign and malignant endothelial cells (Ecs). In normal skin with quiescent ECs, no detection by immunohistoc hemical staining wa observed for Bcl-x(L), Bcl-x(s), or Bcl-2. However , in diseased skin samples that feature a prominent angiogenic respons e such as in psoriasis or pyogenic granulomas, the proliferating ECs m arkedly overexpressed Bcl-x(L), with little to no Bcl-2. IN an acquire d-immune-deficiency-syndrome-related neoplasm, Kaposi's sarcoma, the s pindle-shaped tumor cells also overexpressed Bcl-x(L) compared with Bc l-2. These in vivo studies were extended in vitro using cultured ECs a nd kaposi's sarcoma tumor cells that were examined by flow cytometry a nd immunoblot analysis. Both cultured ECs and Kaposi's sarcoma tumor c ells express significantly higher levels of Bcl-x(L) than Bcl-2. Such overexpression of cell survival gene products may contribute to prolon ging the longevity of EC-derived cells in several different benign and neoplastic skin disorders that are characterized by a prominent angio genic tissue response.