PO-061 BCL-2 family of proteins, BCL-XL and MCL-1, regulate apoptosis and cancer cell survival by different mechanisms

Abstract

U-CLL (Unmutated-Chronic Lymphocytic Leukaemia) and M-CLL (Mutated-Chronic Lymphocytic Leukaemia),suggesting a possible correlation between the IBtk expression levels and aggressiveness of disease. Recently, we provided the evidence of IBtk as a prognostic marker of CLL progression. Material and methods Ibtk -/-mice were bred with congenic Em-myc transgenic mice, a pre-clinical mouse model of NonHodgkin's Lymphoma, to generate Ibtk -/-Em-myc mice, which were monitored for survival and tumour development. We used flow-cytometry for B cells immunophenotyping. Primary murine B cells were compared using different approaches: proliferation, cell viability and cell death assays. Results and discussions Our data provide the evidence that Ibtk gene increases survival and delays tumour onset in Emmyc mice.Ibtk -/-Em-myc mice mostly developed pre-B lymphoma and to a lesser extent mature B lymphoma, which was consistent with the tumour phenotype of Em-myc mice.Loss of Ibtk substantially reduced the number of premalignant Blymphoid cells without affecting their proliferation rate. In particular, pre-cancerous immature B cells were reduced in bone marrow and spleen of Ibtk -/-Em-myc compared to Ibtk +/ + Em myc mice.In Em-myc mice, the pre-cancerous state is characterised by aberrant proliferation of B-lymphoid cells, which is initially offset by pro-apoptotic action of c-Myc.We have previously shown that the enhanced expression of IBtk in CLL cells down regulate the expression of pro-apoptotic genes, thus counteracting apoptosis.According to this hypothesis, we found an increased spontaneous apoptosis of pre-cancerous Ibtk Introduction The ability to resist anoikis, a form of apoptosis triggered by detachment of non-malignant epithelial cells from the extracellular matrix (ECM), is thought to be critical for breast tumour invasion and metastasis. ErbB2/Her2, an oncoprotein often overproduced by breast cancer cells, blocks anoikis of breast cancer cells via mechanisms that are not well understood. Our goal is to understand these mechanisms. Material and methods We studied the expression of a transcription factor Irf6, an important mediator of the mammary gland homeostasis, in non-malignant breast epithelial cells MCF-10A and non-malignant primary human mammary epithelial cells (HMEC) before and after their detachment from the ECM. We also examined Irf6 expression in detached ErbB2-overproducing breast cancer cells. We used small interfering RNAs (siRNAs) to knock down Irf6 in the non-malignant cells, infected breast tumour cells with an Irf6-encoding retrovirus to overexpress Irf6 and measured detachmentinduced apoptosis of the cells before and after the indicated changes in Irf6 expression. Results and discussions We found that detachment of MCF-10A or HMEC cells upregulates Irf6 and that Irf6 upregulation promotes their anoikis. We established that ErbB2 downregulates Irf6 in detached breast cancer cells. We also found that an anti-ErbB2 antibody trastuzumab and a small molecule ErbB2 inhibitor lapatinib used for ErbB2-po...