Resumen de Mechanisms behind the oncogene-induced senescence (OIS) – oncogene-induced apoptosis (OIA) decision in cells expressing p95HER2
Cristina Bernadó Morales
In response to oncogenic stresses cells activate two different tumor suppressor mechanisms: Oncogene-induced senescence (OIS), a terminal cell proliferation arrest, or Oncogene-induced apoptosis (OIA), which leads to cell disintegration. We have shown that the oncogene p95HER2-611 leads cells to OIS and that senescent cells increase the ability of neighbor proliferating breast cancer cells to metastatize. In contrast, available evidence indicates that OIA does not have this undesirable side effect. The mechanisms by which an oncogenic insult results in OIS or OIA remains poorly characterized. In this work, we addressed the functional characterization and the mechanism of activation of another previously described, but uncharacterized, p95HER2 fragment, the p95HER2-648. We showed that the expression of p95HER2-648 does not lead to senescence but to apoptosis. In vivo data shows that p95HER2611-induced senescent cells favor the metastatic capability of MDA-MB-231 cells while p95HER2-648-induced apoptotic cells do not have this effect. We observed that cells bearing p95HER2-611 seem to be protected from apoptosis. Consistently, cells expressing p95HER2-611 show increased levels of p21, a wellknown cell cycle regulator and also an apoptotic repressor. Knockdown of p21 in these cells shows increased apoptosis indicating that p21 is protecting senescent cells against apoptosis. We conclude that the expression of different active p95HER2 fragments can lead to either apoptosis or senescence, indicating that HER2 signaling can induce both cellular responses depending on the activated pathways. Elucidating the complete mechanism by which these pathways are activated could help to find a way to promote apoptosis on senescent cells, in order to avoid their pro-metastatic effect.
