Biomedical subjects
Publications and source records attributed to Alun Thomas.
We present a method that for the marriage node graph of a zero-loop pedigree will enumerate all possible pedigrees that share the same underlying tree structure. The enumeration method leads naturally to a scheme for simulating from a uniform distribution on such pedigrees. This is extended to simulating pedigrees for which the underlying marriage node graph is a tree of any particular size.
EB1089, a novel vitamin D3 analog, has been shown to have cytotoxic and antiproliferative properties in a variety of malignant cells. However, its potential as a treatment for B-cell chronic lymphocytic leukemia (B-CLL) has not been evaluated. EB1089 induced apoptosis in all of the 102 B-CLL samples tested with a mean LD(50) (the concentration of EB1089 required to kill 50% of cells) value (+/- SD) of 2.1 x 10(-8) M (+/- 1.4 x 10(-8) M). Furthermore, no significant difference was found in the cytotoxicity of EB1089 in B-CLL samples from previously treated and untreated patients (P =.1637). Induction of apoptosis was associated with a reduction in Bcl-2 and Mcl-1 protein expression, but this was evident only in the apoptotic cells. In contrast, the expression of Bax, p21, and p53 was not altered in the viable or apoptotic cells from either B- or T-lymphocyte lineages. EB1089-induced apoptosis was preceded by activation of p38 mitogen-activated protein (MAP) kinase and suppression of extracellular signal-regulated kinase (ERK) activity, and this was associated with downstream activation of caspase-3. The pancaspase inhibitor (Z-VAD-FMK) and the caspase-9 inhibitor (Z-LEHD-FMK) were able to partially abrogate the apoptotic effects of EB1089 but did not affect the phosphorylation of p38 MAP kinase or the suppression of ERK. The B-CLL cells in the study were shown to highly express vitamin D receptor, but an additional receptor-independent mechanism of cell killing cannot be ruled out at this stage. These findings show that EB1089 is a potent apoptosis-inducing agent in B-CLL cells and may be useful in the treatment of B-CLL patients, particularly those with p53 mutations or drug-resistant disease.
The genome of the japonica subspecies of rice, an important cereal and model monocot, was sequenced and assembled by whole-genome shotgun sequencing. The assembled sequence covers 93% of the 420-megabase genome. Gene predictions on the assembled sequence suggest that the genome contains 32,000 to 50,000 genes. Homologs of 98% of the known maize, wheat, and barley proteins are found in rice. Synteny and gene homology between rice and the other cereal genomes are extensive, whereas synteny with Arabidopsis is limited. Assignment of candidate rice orthologs to Arabidopsis genes is possible in many cases. The rice genome sequence provides a foundation for the improvement of cereals, our most important crops.
The aim of this study was to investigate the effects of all-trans retinoic acid (ATRA) on apoptosis induction, Bcl-2 family protein expression, and differentiation in B-cell chronic lymphocytic leukaemia (B-CLL) cells. ATRA induced apoptosis in all the B-CLL samples tested, and this was accompanied by a specific reduction in Bcl-2 and Mcl-1 protein expression in the apoptotic cells. In contrast, Bax, p21, and p53 expression was not altered in either the viable or apoptotic B-CLL cells, inferring that ATRA utilises a p53-independent cell death pathway. Caspase-3 activation was shown to be a prerequisite for ATRA-induced apoptosis, which was inhibited by the pan-caspase inhibitor Z-VAD-FMK and the caspase-9 inhibitor Z-LEHD-FMK. In addition, the retinoic acid receptor (RAR) antagonist AGN194310 failed to abrogate the apoptotic effects of ATRA, indicating that RAR binding was not necessary for ATRA-induced apoptosis. Furthermore, there was no evidence of ATRA-induced differentiation of the B-CLL cells in this study either in terms of altered morphology or immunophenotype. In summary these data indicate that ATRA induces apoptosis via the intrinsic apoptotic pathway, and this is independent of RAR binding, p53 activation, and cellular differentiation in B-CLL cells.
Our previous work demonstrated that antisense oligonucleotides complementary to Bcl-2 mRNA sequences were able to reduce Bcl-2 protein expression in B-cell chronic lymphocytic leukaemia (B-CLL) cells. Furthermore, the reduction in Bcl-2 expression led to an increase in apoptotic cell death that was associated with an increase in Bax expression. In this present study antisense oligonucleotides directed towards the Bax translation initiation sequence were employed to determine whether Bcl-2 and Bax protein expression were interdependent upon one another and whether Bcl-2 antisense-induced apoptosis was mediated through a p53-dependent cell death pathway. The antisense oligonucleotide down-regulated Bax protein expression between 23.7 and 68.8% in the 20 B-CLL samples tested and significantly inhibited apoptotic cell death when compared to controls (p = 0.0001). Furthermore, these changes were independent of Bcl-2 expression suggesting that the previously observed increase in Bax expression following exposure of B-CLL cells to Bcl-2 antisense oligonucleotides was probably caused by the induction of apoptosis rather than a rheostatic response to the reduction in Bcl-2 protein expression. This notion was substantiated by the fact that p21 expression was induced in Bcl-2 antisense-treated B-CLL cells, a finding consistent with p53 activation.
Li Fraumeni syndrome (LFS) is characterised by a predisposition to the early onset of certain tumors and is associated with germline mutation of the anti-oncogene p53. In this study we analysed the in vitro responses of lymphocytes from two LFS patients to chemotherapeutic drugs in terms of apoptosis induction and the expression of key intracellular proteins that regulate this process. One of the LFS patients also suffered from B-cell chronic lymphocytic leukemia (B-CLL) and hence presented with a light-chain restricted B-cell lymphocytosis while the other patient had entirely normal blood counts. The B-lymphocytes from both LFS patients showed a marked degree of resistance to chlorambucil and fludarabine when compared to age-matched controls but were remarkably sensitive to the novel flavone, flavopiridol. Loss of function of p53 was demonstrated by a failure to induce Bax and p21 protein expression. In addition, altered basal expression patterns of Bcl-2 and Bax, two key regulators of apoptosis, were found in the LFS lymphocytes when compared with controls. These results suggest that LFS lymphocytes carrying a p53 mutation show intrinsic resistance to conventional chemotherapeutic drugs and this is associated with dysregulation of Bcl-2 family proteins. Furthermore, The innate resistance profile was similar in leukemic and non-leukemic lymphocytes and was therefore independent of genetic changes acquired during malignant transformation. Novel agents that induce p53-independent cell killing may be useful not only in the treatment of LFS-associated tumors but also drug resistant tumors in general where p53 and/or Bcl-2 family dysregulation is a feature.