Resistance to apoptotic cell death in a drug resistant T cell leukaemia cell line

In this study, we investigated the responses of the T cell leukaemia cell line, CCRF-CEM, and a vincristine-resistant subline, CEM/VCR R, to the induction of cell death by serum withdrawal. This treatment was used to overcome any contribution of P-glycoprotein-mediated drug resistance to the responses of the CEM/VCR R cells. Following serum withdrawal both cell lines exhibited typical apoptotic responses including morphological changes and nucleosomal cleavage of the DNA. However, using several different assays for cell death the CEM/VCR R cell line was shown to undergo apoptosis at a slower rate than the parental CCRF-CEM cell line. Expression of c-Myc, Bcl-2 and p53 was found to be similar in both cell lines, discounting involvement of these proteins in the observed difference in apoptotic response. Given our previous finding that reorganisation of tubulin is involved in apoptosis, we examined the expression of alpha-, beta- and acetylated alpha-tubulin in the parental and resistant lines. The CEM/VCR R cell line had altered tubulin expression when compared to that of the CCRF/CEM line. Transnuclear microtubule networks were observed in log phase CEM/VCR R cells. In addition, increased expression of the acetylated form of the alpha-tubulin isotype suggested that a more stable microtubule network was present in the CEM/VCR R cells. These findings imply that the drug-resistance phenotype in the CEM/VCR R cells may involve the suppression of apoptosis, and that the development of an altered microtubule network may contribute to this suppression.