Expression of Bcl-XS alters cytokinetics and decreases clonogenic survivalin K12 rat colon carcinoma cells

bcl-XS, a member of the bcl-2 family, has been shown to induce and/or sensi tize some cells to undergo programmed cell death, and to negate the anti-ap optotic activity of bcl-XL and bcl-2 by mechanisms which are still uncertai n. To help understand these mechanisms we have established stable derivativ es of the K12 rat colon carcinoma cell line that express bcl-XS in a tetrac ycline-regulated manner, using an autoregulatory retroviral cassette. When bcl-XS expression is induced, we observe two phenotypic responses. A small fraction of cells appear to undergo spontaneous apoptosis while the majorit y of cells undergo a form of cytostasis. In the latter case, the cells stop dividing (or divide a limited number of times at a retarded rate) and swel l to many times their original size. These cells can take on a ghostlike ap pearance and subsequently detach from the culture plates and die or they ma y remain intact in a hindered state of proliferation. Doubling times were c alculated to be 31.4 h in the presence of tetracycline and 50.4 h without t etracycline, bcl-XS expression also causes dramatic alterations in the cell cycle distribution of K12 cells manifesting as a substantial decrease (app roximate to 50%) in the fraction of S phase cells with a concomitant increa se in the G1 population. Continuous expression of bcl-XS, at levels approxi mately equal to that of bcl-XL, decreased the viability of K12 cells as dem onstrated by a log decline in clonogenic survival. This decrease occurred w ithout considerable apoptosis or a compensatory increase in the level of bc l-XL. None of these phenotyes were present in control cells expressing beta -galactosidase in a similar retroviral cassette. These observations demonst rate that bcl-XS can have substantial cytokinetic effects under circumstanc es that produce relatively little apoptosis.