CONICET | Buscador de Institutos y Recursos Humanos

Introduction: HSPB1 (Hsp27) is usually over-expressed in breast cancers affecting the disease outcome and the sensitivity of tumors to chemotherapy and radiotherapy. This protein interacts with other proteins like beta-catenin, a recent study reported that histone deacetylase HDAC6, transcription factor STAT2 and procaspase-3 were degraded in human cancerous cells displaying genetically decreased levels of Hsp27. Phosphatase and Tensin homologue (PTEN) is a tumor suppressor gene that is deleted in many human tumors, it is involved in the regulation of various cellular processes. The PI3K/Akt signaling pathway is negatively regulated by PTEN. Hsp27 is described as a key components of the Akt signaling cascade: Akt, BAD, FKHR, Hsp27, mitogen-activated protein (MAP) kinase kinase-3 and -6 (MKK3/6).Objectives: To examine whether the down-regulation of Hsp27 affects the PTEN levels in the MCF-7 human breast cancer cell line.Methodology: We examined MCF-7 cells transfected with siHsp27. PTEN was detected with two different antibodies using western blots and immunocytochemistry. p-Akt was also evaluated by western blot. In addition, Hsp27 was immunoprecipitated to know whether this protein interacts with PTEN. Co-localization studies were also carried out by confocal microscopy.Results: A significant reduction in the Hsp27 levels was noted in the siHsp27 transfected cells. In these transfected cells the down-regulation of Hsp27 was accompanied by PTEN up-regulation. The MW 76 kDa and 55 kDa PTEN forms were up-regulated as revealed by two different antibodies. The phosphatase activity of PTEN seems to be active because p-Akt levels were reduced. The immunoprecipitation of Hsp27 was bringing PTEN, and the two proteins seem to interact at cytoplasmic level.Conclusions: The down-regulation of Hsp27 modulates PTEN levels in human breast cancer cells suggesting an interaction between these two molecules.