Project description:The cyclin-dependent kinase inhibitor p21WAF1/Cip1 (p21) is a cell-cycle checkpoint effector and inducer of senescence, regulated by p53. Yet, evidence suggests that, through a so-far obscure mechanism, p21 could also be oncogenic. We report that a subset of atypical cancerous cells strongly expressing p21 showed proliferation features. This occurred predominantly in p53-mutant human cancers suggesting p53-independent upregulation of p21 selectively in more aggressive tumour cells. Multifaceted phenotypic and genomic analyses of p21-inducible, p53-null, cancerous and near-normal cellular models showed that after an initial senescence-like phase, a subpopulation of p21-expressing proliferating cells emerged, featuring increased genomic instability, aggressiveness and chemo-resistance. Mechanistically, sustained p21-accumulation inhibited mainly the CRL4CDT2 ubiquitin-ligase, leading to deregulated origin licensing and replication stress. Collectively, our data reveal tumour-promoting ability of p21 through deregulation of DNA replication licensing machinery, an unorthodox role to be considered in cancer treatment, since p21 responds to various stimuli including some chemotherapy drugs.
Project description:The cyclin-dependent kinase inhibitor p21WAF1/Cip1 (p21) is a cell-cycle checkpoint effector and inducer of senescence, regulated by p53. Yet, evidence suggests that, through a so-far obscure mechanism, p21 could also be oncogenic. We report that a subset of atypical cancerous cells strongly expressing p21 showed proliferation features. This occurred predominantly in p53-mutant human cancers suggesting p53-independent upregulation of p21 selectively in more aggressive tumour cells. Multifaceted phenotypic and genomic analyses of p21-inducible, p53-null, cancerous and near-normal cellular models showed that after an initial senescence-like phase, a subpopulation of p21-expressing proliferating cells emerged, featuring increased genomic instability, aggressiveness and chemo-resistance. Mechanistically, sustained p21-accumulation inhibited mainly the CRL4CDT2 ubiquitin-ligase, leading to deregulated origin licensing and replication stress. Collectively, our data reveal tumour-promoting ability of p21 through deregulation of DNA replication licensing machinery, an unorthodox role to be considered in cancer treatment, since p21 responds to various stimuli including some chemotherapy drugs.
Project description:The p21 protein, encoded by CDKN1A, plays a vital role in the induction of senescence, and its transcriptional control by p53 tumour supressor is well-established. However, p21 can also be regulated in a p53-independent manner, by mechanisms that remain poorly understood. Therefore, we here used a chromatin-directed proteomic approach and identified ZNF84 as a novel regulator of p21 in various p53-deficient cell lines.
Project description:SETD1A, a member of the Set1/COMPASS family maintaining H3K4 methylation in the promoters of transcriptionally active genes, is critical for the execution of developmental gene expression and is overexpressed in multiple cancers including breast cancer1-3. Here we show that SETD1A is essential for supporting cellular mitotic processes and consequentially, its depletion leads to senescence. SETD1A directly regulates the expression of several genes orchestrating mitosis and DNA damage responses and its depletion results in multiple mitotic defects including chromosome misalignment and segregation defects. Senescence-associated cell cycle arrest in SETD1A knockdown cells is independent of the mutational status of p53, RB and p16, key mediators of this process, instead, is sustained through direct transcriptional suppression of SKP2, the ubiquitin ligase, which degrades p27 and p21. Rare cells escape senescence and re-enter the cell cycle by restoring SKP2 expression but with enhanced genomic instability. In >200 cancer cell lines and in primary circulating tumor cells, expression of SETD1A correlates with genes involved in mitosis and cell cycle suggesting a role in suppressing senescence induced by aberrant mitosis. Thus, SETD1A encodes a chromatin modifier, whose modulation may maintain the balance between senescence and genomic instability in cells.
Project description:Cisplatin treatment causes genome instability by single-strand annealing (SSA) activation in some cancer cells. Therefore, we checked whether EGC, a RAD52 inhibitor, can restrain genome instability induced by cisplatin treatment.
Project description:Nuclear speckles are prominent nuclear bodies that contain a myriad of factors involved in gene expression. The role of nuclear speckles as activating transcriptional compartments is emerging. However, the extent that the association between speckles and DNA is regulatable, and the mechanisms that govern regulated speckle association are currently unclear. Using DNA- and RNA-FISH, we show that speckle association can be mediated by the p53 transcription factor, finding that p53 activation drives speckle association of specific p53 transcriptional targets. Analysis of a key p53 target, p21, revealed an increase in nascent transcripts at speckle-adjacent transcription sites, supporting a role for speckles in amplifying transcriptional output. Importantly, p53-regulated speckle association of p21 did not depend on transcriptional activation, demonstrating that speckle association is not merely a consequence of gene expression. In contrast, speckle association of p21 did require DNA binding functions of p53, providing a mechanism for the specificity by which speckle association is regulated. Beyond p21, a substantial subset of p53 targets have p53-regulated speckle association, while other p53 targets do not, and we find that genomic context is highly deterministic of which target genes have regulated speckle association. These findings reveal a novel means by which transcription factors may control gene expression and provide a mechanism for the specificity of regulated speckle association.