The homeoprotein SIX1 controls cellular senescence through the regulation of p16INK4A and differentiation-related genes

Cellular senescence is an antiproliferative response with essential functions in tumor suppression and tissue homeostasis. Here we show that SIX1, a member of the SIX family of homeobox transcriptional factors, is a novel repressor of senescence. Our data show that SIX1 is specifically downregulated in fibroblasts upon oncogenic stress and other pro-senescence stimuli, as well as in senescent skin premalignant lesions. Silencing of SIX1 in human fibroblasts suffices to trigger senescence, which is mediated by p16INK4A and lacks a canonical senescence-associated secretory phenotype. Interestingly, SIX1-associated senescence is further characterized by the expression of a set of development and differentiation-related genes that significantly overlap with genes associated with SIX1 in organogenesis or human tumors, and show coincident regulation in oncogene-induced senescence. Mechanistically, we show that gene regulation by SIX1 during senescence is mediated, at least in part, by cooperation with Polycomb repressive complexes. In summary, our results identify SIX1, a key development regulator altered in human tumors, as a critical repressor of cellular senescence, providing a novel connection between senescence, differentiation and tumorigenesis.

Pathological complete response (pCR) in stage II and III breast cancer patients treated with neoadjuvant chemotherapy (CT): Dose dense ACx4 followed by AT/Tx4 (weekly paclitaxel)

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Background: This is a prospective study of a single Institution to determine the pCR in stage II and II breast cancer patients after dose dense and sequential CT using the most active drugs. Patients and Methods: Between June/2004 and July/2005 we collected 28 patients, they have echocardiogram and needle biopsy for IHC before starting the treatment. All of them received Adriamicin 60mg/m2 in 3hrs infusion and Cyclophosphamide 600mg/m2 x4 in dose dense schedule (every 2 weeks) with G-CSF support and then Adriamicin 60mg/m2 and Taxol 80mg/m2 days 1,8 every 3 weeks. Once the treatment was finished they went to surgery. Results: Six (21%) patients were stage II and 22 (79%) were stage III; 8 (35%) patients achieve pCR, 50% of them had Her2/neu positive and 7/8 (90%) were ER/PR negative; 60% (5) had T more than 5cm and 75% were post menopausal. 12 patients had clinical complete remission. Eight patients had progressive disease with 50% ER/PR negative, 37% Her2/neu positive and all of them with T more than 5cm. 50% were premenopausal. Conclusion: This is one of the highest pCR of the literature (35%) achieved and it is interesting to note that 90% of them were ER/PR negative, so this is a potential target group for CT intensification. There is a group of patients (with progressive disease) that will never respond to CT, and it would be worst in the adjuvant setting (blindly treatment) because the great toxicity. We need more studies to confirm this hypothesis.

No significant financial relationships to disclose.