Resumen de Molecular mechanisms of apoptosis induced by dexamethasone in chronic lymphocytic leukemia

María Joao Gomes Monteiro Lopes Baptista

• Glucocorticoids are frequently included in the chemotherapy regimens administered to patients with CLL because they are potent immunosuppressant agents and because they are able to induce apoptosis in CLL cells. Although used from a long time, the molecular mechanisms by which glucocorticoids induce cell death in CLL cells are largely unknown. Interestingly, CLL cells from prognostic groups defined by the mutational load of the IGHV genes and the expression of ZAP70 seem to have different responses to glucocorticoids. The hypothesis in this thesis is that there are genes or proteins that determine the different response to glucocorticoids among the specific prognostic groups of patients with CLL. Sensitivity to dexamethasone was analyzed ex vivo in 50 CLL and compared according to IGHV mutational status and/or ZAP70 expression. The response was further compared by gene expression profiling (GEP) of selected cases. Expression of genes of interest was validated by quantitative reverse transcriptase PCR. Response to dexamethasone is higher in cases with unmutated IGHV/high ZAP70 expression and the levels of induction of the pro-apoptotic BIM gen correlate with the degree of cell death. The different levels of apoptosis induced by dexamethasone observed in the CLL groups defined by ZAP70 expression translate into different profiles of gene expression. These differences are mainly quantitative; cases with high ZAP70 expression show higher levels of gene induction/repression than cases with low ZAP70 expression. Specific analysis of genes of interest performed in a large series disclosed that baseline mRNA and protein expression levels of FKBP5, the co-chaperone of the glucocorticoid receptor, correlate with the extent of CLL cells apoptosis induced by the treatment with dexamethasone. Baseline FKBP5 levels are higher in samples from patients with high ZAP70 expression. GILZ is differentially induced by dexamethasone in ZAP70 expression groups of CLL, being higher in cases with high ZAP70 expression. Induction of GILZ correlates with induction of BIM and levels of apoptosis. Unmutated IGHV/high ZAP70 CLL cells exhibit better response to dexamethasone treatment, which is accompanied by a differential expression of genes involved in the glucocorticoid-receptor pathway and by an increased induction of genes related to apoptosis.