The limitation of proliferative potential in human somatic cells imposed by replicative senescence has been proposed as a mechanism of tumor suppression. The E3 ubiquitin ligase Smurf2 is up-regulated during replicative senescence in response to telomere shortening, and induces senescence when expressed adventitiously in early passage or telomerase-immortalized human fibroblasts. To investigate the generality of Smurf2's control of cell proliferation, we have studied the effects of Smurf2 up-regulation on cell proliferation in early passage human mammary epithelial cells which normally do not show elevated expression of Smurf2 during senescence, and in 16 human cancer cell lines derived from both sarcomas and carcinomas. Here we report that Smurf2 up-regulation induced senescence in a wide variety of human cell types, including highly neoplastic cell lines. Consistent with our previous findings, the ability of Smurf2 to arrest cell proliferation did not require its ubiquitin ligase activity. Furthermore, expression of the cyclin-dependent kinase inhibitor p21 was increased in tumor cells undergoing Smurf2-induced senescence, and such increase occurred independently of the transactivation function of p53. Our results, which reveal a previously unsuspected tumor suppression function for Smurf2-induced senescence, suggest that modulation of Smurf2 action may be a useful strategy for inhibition of cancer cell growth.
"Lentiviral packaging and infection were carried out as described previously (Zhang et al. 2008). Briefly, lentiviral vectors were co-transfected into 293T cells with a plasmid (pMD2.VSV-G) encoding vesicular stomatitis virus glycoprotein (VSV-G) and a plasmid (pCMVdR8.74) "
[Show abstract][Hide abstract] ABSTRACT: The inhibitor of differentiation or DNA binding (Id) family of transcription regulators plays an important role in cell proliferation, differentiation, and senescence. However, regulation of Id expression during these processes is poorly understood. Id proteins are known to undergo rapid turnover mediated by the ubiquitin-proteasome pathway. Anaphase-promoting complex has been shown to ubiquitinate Id2, but E3 ubiquitin ligase(s) that ubiquitinate other Id family members are not known. Here, we report for the first time the identification of Smurf2 as the E3 ligase that ubiquitinates Id1 and Id3. Smurf2-mediated ubiquitination and consequent degradation of Id1 or Id3 plays an important role in the regulation of Id expression in senescent cells. Furthermore, we found that Id1 is the mediator through which Smurf2 regulates p16 expression, providing a mechanistic link between Smurf2 and p16 expression during senescence.
[Show abstract][Hide abstract] ABSTRACT: Ubiquitination ofendogenous proteins is one of the key regulatory steps that guides protein degradation through regulation of proteasome activity. During the last years evidence has accumulated that proteasome activity is decreased during the aging process in various model systems and that these changes might be causally related to aging and age-associated diseases. Since in most instances ubiquitination is the primary event in target selection, the system ofubiquitination and deubiquitination might be of similar importance. Furthermore, ubiquitination and proteasomal degradation are not completely congruent, since ubiquitination confers also functions different from targeting proteins for degradation. Depending on mono- and polyubiquitination and on how ubiquitin chains are linked together, post-translational modifications of cellular proteins by covalent attachment of ubiquitin and ubiquitin-like proteins are involved in transcriptional regulation, receptor internalization, DNA repair, stabilization of protein complexes and autophagy. Here, we summarize the current knowledge regarding the ubiquitinome and the underlying ubiquitin ligases and deubiquitinating enzymes in replicative senescence, tissue aging as well as in segmental progeroid syndromes and discuss potential causes and consequences for aging.
Advances in Experimental Medicine and Biology 01/2010; 694:172-96. DOI:10.1007/978-1-4419-7002-2_13 · 1.96 Impact Factor
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