Killing of sarcoma cells by proapoptotic Bcl-X(S): role of the BH3 domain and regulation by Bcl-X(L).
Kaposi's sarcoma (KS) is the most common tumor affecting AIDS patients with over 20% of these patients afflicted by this disease. Previous studies have demonstrated that KS tumor cells predominantly express the prosurvival protein Bcl-X(L) compared with Bcl-2. In the current study, we have used an adenoviral vector that expresses Bcl-X(S), a functional inhibitor of Bcl-X(L), to study the significance of Bcl-X(L) expression in the KS cell line (SLK) or KS primary cultures. The results demonstrate that 75% to 80% of SLK or KS primary cells were killed by the Bcl-X(S) containing adenovirus whereas KS cells infected with control adenovirus showed no significant cell death or growth inhibition. Overexpression of Bcl-X(L), but not Bcl-2, in SLK cells attenuated apoptosis induced by adenovirus Bcl-X(S). Immunoprecipitation experiments revealed that adenoviral Bcl-X(S) associated with Bcl-X(L), but not with Bcl-2. Mutational analysis showed that the alpha 2 helical region of Bcl-X(S) containing the BH3 motif was critical for killing activity and interaction with Bcl-X(L). These results suggest that Bcl-X(S) is a direct killer and Bcl-X(L) may act by interacting with and sequestering Bcl-X(S.) These studies also suggest that targeting Bcl-X(L) may be of therapeutic benefit for the treatment of tumors that are characterized by inappropriate expression of Bcl-X(L).
Mitra
R S
RS
Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Benedict
M A
MA
Qian
D
D
Foreman
K E
KE
Ekhterae
D
D
Nickoloff
B J
BJ
Nuñez
G
G
D000256:Adenoviridae / Q000235:genetics; D017209:Apoptosis; D005822:Genetic Vectors; D006801:Humans; D015151:Immunoblotting; D008297:Male; D009062:Mouth Neoplasms / Q000378:metabolism / Q000473:pathology*; D009154:Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012514:Sarcoma, Kaposi / Q000378:metabolism / Q000473:pathology*; D014407:Tumor Cells, Cultured; D051020:bcl-X Protein; D018909:src Homology Domains / Q000502:physiology*
C494811:BCL2L1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein