The ChIP has been calculated as binding to region of interest IgG control, divided by binding to negative control region IgG control. The following primers were used Patient samples As required by the French Committee for the Protection of Human Subjects, informed consent was obtained from study patients to use their surgical specimens and clinicopathological data for research purposes, and the local ethic committee approved protocols. Statistical analysis of published e pression data The impact of HER2 status on the e pression of 20 genes of the Bcl 2 family was evaluated by means of Wilco on test. When the evaluation was performed in a probe match ing way, 2 pooled published cohorts for which Affyme tri data were available were used after their conversion to a common scale.

In a gene matching approach the evaluation was performed on a larger pool obtained by merging 5 genomic published cohorts. If multiple probes corresponded to a same gene, the median of probes was taken. Results Mcl 1 is highly e pressed in HER2 overe pressing cancers, and is required to maintain the survival of HER2 overe pressing cells in vitro The HER2 amplified BT474 breast cancer e press detect able levels of the main anti apoptotic Bcl 2 homologues Bcl L, Bcl 2 and Mcl 1. We investigated whether any of these proteins play a crucial role in main taining the viability of BT474 cells in vitro using a RNA interference approach based on the transfection of small interfering RNAs targeting Bcl L, Bcl 2 or Mcl 1. Transfection with control siRNA did not impact on the e pression of these proteins compared to that found in non transfected cells.

In contrast, transfection of BT474 cells with the targeted siRNA led to the selective down regulation of the targeted proteins 48 hours after treatment. We analyzed the consequence of Bcl L, Bcl 2 and Mcl 1 depletion, under these conditions, on the viability of BT474 cells. We mea sured the e pression, by the transfected cells, of the APO2. 7 antigen, whose e pression is restricted to dying, apoptotic cells. As shown in Figure AV-951 1B, knock down of Mcl 1 e pression by RNA interference lead to the induction of apoptosis in a substantial fraction of cells. In contrast, depletion of either Bcl L or Bcl 2 did not induce apoptosis in BT474 cells. Induction of cell death, and of apoptosis, by Mcl 1 depletion in BT474 cells was also confirmed by a trypan blue staining proce dure and by Anne in V staining followed by flow cytometry analysis.

Thus, Mcl 1 is specifically involved in preventing BT474 cells from spon taneously undergoing apoptosis. Interestingly, we found that this feature of Mcl 1 dependence was displayed by another HER2 overe pressing cell line, SKBR3, as transfection with Mcl 1 siRNA was sufficient to induce rates of apoptosis in these cells also.