Cellular senescence has been considered a novel target for cancer therapy. It has also been pointed out that p21cip1/waf1 and p27kip1 cyclin-dependent kinase inhibitors (CKIs) play a role in cellular senescence in some tumor types. Therefore, in order to address the possibility of a cooperative role between p21 and p27 proteins in senescence in vivo we analyzed cellular senescence in spontaneous glandular proliferative lesions (adrenal, thyroid and pituitary glands) in a double-KO mice model, using ?H2AX, p53, p16, PTEN and Ki67 as senescence markers. The results obtained showed that p21p27 double-null mice had the lowest number of ?H2AX positive cells in glandular hyperplasias and benign tumors. Also, in this group, Ki67 proliferation index correlated with a lower immunohistochemical expression of ?H2AX and p53. The expression of p16 and PTEN do not seem to cause synergism of senescence in the benign lesions analyzed in p21p27 double-KO mice. These observations suggest an intrinsic cooperation between p21 and p27 CKIs in the activation of stress-induced cellular senescence and tumor progression in vivo, which would be a physiological mechanism to prevent tumor cell proliferation.
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