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

Abstract

bcl-XS, a member of the bcl-2 family, has been shown to induce and/or sensitize some cells to undergo programmed cell death, and to negate the anti-apoptotic activity of bcl-XL and bcl-2 by mechanisms which are still uncertain. To help understand these mechanisms we have established stable derivatives of the K12 rat colon carcinoma cell line that express bcl-XS in a tetracyclineregulated 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 majority 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 swell to many times their original size. These cells can take on a ghostlike appearance and subsequently detach from the culture plates and die or they may remain intact in a hindered state of proliferation. Doubling times were calculated to be 31.4 h in the presence of tetracycline and 50.4 h without tetracycline, bcl-XS expression also causes dramatic alterations in the cell cycle distribution of K12 cells manifesting as a substantial decrease (&50%) in the fraction of S phase cells with a concomitant increase in the G1 population. Continuous expression of bcl-XS, at levels approximately equal to that of bcl-XL, decreased the viability of K12 cells as demonstrated by a log decline in clonogenic survival. This decrease occurred without considerable apoptosis or a compensatory increase in the level of bcl-XL. None of these phenotypes were present in control cells expressing b-galactosidase in a similar retroviral cassette. These observations demonstrate that bcl-XS can have substantial cytokinetic e ects under circumstances that produce relatively little apoptosis.

Deadly decisions: the role of genes regulating programmed cell death in human preimplantation embryo development

“…Using an antisense mRNA approach in murine embryos, we observed that the classical Bcl-xL isoform is not required for progression of eightcell embryos through the blastocyst stage. In contrast, upregulation of the alternative splicing form Bcl-xS renders blastomeres more susceptible to death and cell cycle arrest , as previously observed in other cell types (Fridman et al 1998, Lindenboim et al 2000, suggesting that this gene may be an important component of the regulation of embryonic fate. Among other anti-apoptotic Bcl-2 family members, Bcl-w and Bfl-1/A1 are only weakly and inconsistently expressed (Jurisicova et al 1998a, Metcalfe et al 2004) and thus are unlikely to play a part in regulating early embryo demise.…”

The Role of Bcl-XSin Radiation Sensitivity

“…Several studies have demonstrated that Bcl-X S expression enhances the sensitivity and apoptosis of cancer cells in response to chemotherapeutic agents (8)(9)(10). The effect of Bcl-X S expression on cell survival has also been assessed in both in vivo animal tumor models (25) and in vitro clonogenic survival assays (15). These studies have provided strong evidence for the role Bcl-X S in apoptosis and chemosensitization.…”

“…In contrast to previous studies, we have employed a tetracycline-regulated expression system to evaluate the effect of Bcl-X S expression on radiation survival. Initial studies carried out in this system showed that Bcl-X S expression induced rapid cell death in NIH 3T3 fibroblasts and reduced clonogenic survival in rat colon carcinoma cells (15,16). Bcl-X S -induced cell death occurred independent of caspase activation and was associated with cytochrome c depletion and loss of mitochondrial membrane potential (16,17).…”

Inhibition of RUNX2 Transcriptional Activity Blocks the Proliferation, Migration and Invasion of Epithelial Ovarian Carcinoma Cells

“…Thus, RUNX2 knockdown resulted in upregulation of gene nodes/genes known to be implicated in apoptosis induction or displaying TSG functions (see Figure 7A). Notably the UBC interaction network and its members were shown to decrease in anchorage-independent cell growth and increase apoptosis, suggesting UBC may act as a negative regulator of skin carcinogenesis [48]; CRYAB has been reported as a potential TSG [49], while increased expression of BCL-XS (BCL2L1) protein in tumors was associated with decreased proliferation and induction of apoptosis [50], [51]. Similarly, CTGF upregulation was found to be associated with apoptosis and decrease of tumor cell invasion [52]–[54]; PPM1A (PP2C) expression could induce cell cycle arrest and apoptosis via activation of the p53 pathway [55], and NF2 has been characterized as a TSG in different cancers [56]–[58].…”