OVEREXPRESSION OF BAX GENE SENSITIZES K562-ERYTHROLEUKEMIA-CELLS TO APOPTOSIS INDUCED BY SELECTIVE CHEMOTHERAPEUTIC-AGENTS

Bax and Bcl-2 are a pair of important genes that control programmed ce ll death, or apoptosis, with Bax being the apoptosis promoter and Bcl- 2 the apoptosis protector, Although the detailed mechanism is unknown, the protein products of these two genes form protein dimers with each other and the relative ratio of the two proteins is believed to be a determinant of the balance between life and death, In our preliminary study, we found that K562 erythroleukemia cells have an extremely low level of endogenous Bcl-2 expression and a fairly high level of endoge nous Bar expression, We constructed Bar and Bcl-2 expression vectors a nd transfected them into K562 cells, We found that transfection of Bar vector increased the expression of Bar protein; a shortened form of B ar also appeared, Cell death analysis using the Annexin V assay showed that the Bax vector caused significantly more apoptotic cells that th e Bcl-2 or pCI-neo vector did, After selection with G418, Bar, Bcl-2 a nd pCI-neo stably transfected cells were established, These three cell Lines were examined for their response to the chemotherapeutic agents ara-C, doxorubicin, etoposide and SN-38. Bax-K562 cells showed signif icantly higher fractions of apoptotic cells than pCI-neo-K562 cells wh en treated with ara-C, doxorubicin or SN-38. No sensitization effect w as seen when etoposide was used, In contrast, Bcl-2-K562 cells had few er apoptotic cells than pCI-neo-K562 cells after treatment with all th ese agents, Therefore, Bar may sensitize K562 cells to apoptosis induc ed by a wide range of, but not all, chemotherapeutic agents.