Tumor suppressor p53 is a transcription factor that regulates a large number of genes and guards against genomic instability. Under multiple cellular stress conditions, p53 functions to block cell cycle progression transiently unless proper DNA repair occurs. Failure of DNA repair mechanisms leads to p53-mediated induction of cell death programs. p53 also induces permanent cell cycle arrest known as cellular senescence. During neoplastic progression, p53 is often mutated and fails to efficiently perform these functions. It has been observed that cancers carrying a wild-type p53 may also have interrupted downstream p53 regulatory signaling leading to disruption in p53 functions. Therefore, strategies to reactivate p53 provide an attractive approach for blocking tumor pathogenesis and its progression. p53 activation may also lead to regression of existing early neoplastic lesions and therefore may be important in developing cancer chemoprevention protocols. A large number of small molecules capable of reactivating p53 have been developed and some are progressing through clinical trials for prospective human applications. However, several questions remain to be answered at this stage. For example, it is not certain if pharmacological activation of p53 will restore all of its multifaceted biological responses, assuming that the targeted cell is not killed following p53 activation. It remains to be demonstrated whether the distinct biological effects regulated by specific post-translationally modified p53 can effectively be restored by refolding mutant p53. Mutant p53 can be classified as a loss-of-function or gain-of-function protein depending on the type of mutation. It is also unclear whether reactivation of mutant p53 has similar consequences in cells carrying gain-of-function and loss-of-function p53 mutants. This review provides a description of various pharmacological approaches tested to activate p53 (both wild-type and mutant) and to assess the effects of activated p53 on neoplastic progression.
"Thus, restoration of tumor suppressor gene function is considered as a rational approach for therapeutic intervention of carcinogenesis. For instance, the pharmacological activation of a tumor suppressor protein, p53, is being widely studied for the development of new cancer chemotherapeutics (22). Like many other tumor suppressor proteins, the expression of Tob1 is frequently lost in various cancers. "
[Show abstract][Hide abstract] ABSTRACT: Transducer of ErbB-2.1 (Tob1), a tumor suppressor protein, is inactivated in a variety of cancers including stomach cancer. However, the role of Tob1 in gastric carcinogenesis remains elusive. The present study aimed to investigate whether Tob1 could inhibit gastric cancer progression in vitro, and to elucidate its underlying molecular mechanisms. We found differential expression of Tob1 in human gastric cancer (MKN28, AGS and MKN1) cells. The overexpression of Tob1 induced apoptosis in MKN28 and AGS cells, which was associated with sub-G1 arrest, activation of caspase-3, induction of Bax, inhibition of Bcl-2 and cleavage of poly (ADP-ribose) polymerase (PARP). In addition, Tob1 inhibited proliferation, migration and invasion, which were reversed in MKN1 and AGS cells transfected with Tob1 siRNA. Overexpression of Tob1 in MKN28 and AGS cells induced the expression of Smad4, leading to the increased expression and the promoter activity of p15, which was diminished by silencing of Tob1 using specific siRNA. Tob1 decreased the phosphorylation of Akt and glycogen synthase kinase-3β (GSK3β) in MKN28 and AGS cells, resulting in the reduced protein expression and the transcriptional activity of β‑catenin, which in turn decreased the expression of cyclin D1, cyclin-dependent kinase-4 (CDK4), urokinase plasminogen activator receptor (uPAR) and peroxisome proliferator and activator receptor-δ (PPARδ). Conversely, silencing of Tob1 induced the phosphorylation of Akt and GSK-3β, and increased the expression of β‑catenin and its target genes. Collectively, our study demonstrates that the overexpression of Tob1 inhibits gastric cancer progression by activating Smad4- and inhibiting β‑catenin-mediated signaling pathways.
International Journal of Oncology 06/2012; 41(3):839-48. DOI:10.3892/ijo.2012.1517 · 3.03 Impact Factor
"While some of these compounds directly interact with mutant p53 proteins and reestablish their functions via conformational effects (Athar et al, 2011; Selivanova, 2010; Wiman, 2010), others were designed to inhibit the p53-targeting ubiquitin ligase HDM2, leading to increased p53 concentrations (Shangary & Wang, 2009). Moreover, some agents kill p53-deficient cancer cells based on their increased tendency to undergo polyploidization . "
[Show abstract][Hide abstract] ABSTRACT: The genetic or functional inactivation of p53 is highly prevalent in human cancers. Using high-content videomicroscopy based on fluorescent TP53(+/+) and TP53(-/-) human colon carcinoma cells, we discovered that SP600125, a broad-spectrum serine/threonine kinase inhibitor, kills p53-deficient cells more efficiently than their p53-proficient counterparts, in vitro. Similar observations were obtained in vivo, in mice carrying p53-deficient and -proficient human xenografts. Such a preferential cytotoxicity could be attributed to the failure of p53-deficient cells to undergo cell cycle arrest in response to SP600125. TP53(-/-) (but not TP53(+/+) ) cells treated with SP600125 became polyploid upon mitotic abortion and progressively succumbed to mitochondrial apoptosis. The expression of an SP600125-resistant variant of the mitotic kinase MPS1 in TP53(-/-) cells reduced SP600125-induced polyploidization. Thus, by targeting MPS1, SP600125 triggers a polyploidization program that cannot be sustained by TP53(-/-) cells, resulting in the activation of mitotic catastrophe, an oncosuppressive mechanism for the eradication of mitosis-incompetent cells.
EMBO Molecular Medicine 06/2012; 4(6):500-14. DOI:10.1002/emmm.201200228 · 8.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to investigate the expressions of tumor inhibitor of growth (ING1) gene p33ING1, p53, and autophagy-related gene Beclin1 in human non-small cell lung cancer (NSCLC), and the correlation between their expressions with clinical pathological features and clinical significance. The research can provide new ideas and experimental evidence for early diagnosis and biotherapy for NSCLC in the future. The human NSCLC tissues and surrounding non-cancerous tissues were collected from surgical operation. The expressions of mRNA or protein of p33ING1, p53, and Beclin1 were detected by using of reverse transcription polymerase chain reaction or Western blot in these tissues. The results were used to analyze the relationships between these gene expressions with the developing of NSCLC and clinical pathological features. The expressions of mRNA or protein of p33ING1 and Beclin1 in NSCLC tissues were significantly lower than that in surrounding noncancerous tissues (p < 0.05). The expressions of mRNA or protein of p33ING1 and Beclin1 in well- and middle-differentiated NSCLC tissues were lower than those in poor-differentiated NSCLC tissues (p < 0.05). The expressions of mRNA or protein of p33ING1 and Beclin1 in presence of lymph nodes metastasis were lower than those in absence of lymph nodes metastasis (p < 0.05). The expressions of mRNA or protein of p33ING1 and Beclin1 in patients of pathological stage (stages I-II) were higher than those in pathological stage (stages III-IV) (p < 0.05). But the expression of protein of mutant-type p53 in NSCLC tissues was significantly higher than that in surrounding non-cancerous tissues (p < 0.05). The expressions of protein of mutant-type p53 in well- and middle-differentiated NSCLC tissues were higher than those in poor-differentiated NSCLC tissues (p < 0.05). The expressions of protein of mutant-type p53 in presence of lymph nodes metastasis were higher than those in absence of lymph nodes metastasis (p < 0.05). The expressions of protein of mutant-type p53 in patients of pathological stage (stages I-II) were lower than those in pathological stage (stages III-IV) (p < 0.05). These expression changes of p33ING1, p53, and autophagy-related Beclin1 genes were associated with tumor cell differentiation, lymph nodes metastasis, and pathological stage of NSCLC. But these expression changes of these three genes were not associated with gender, age, size of primary carcinoma, histological type of NSCLC (p > 0.05). The expression of mRNA of p53 and Beclin1 were correlated with p33ING1 mRNA expression in NSCLC tissues (p < 0.05). The activity changes of tumor inhibitor of growth, autophagy, and apoptosis may be related to the emergence and the development of NSCLC. The combined detection of p33ING1, p53, and Beclin1 genes and proteins will be helpful for early diagnosis and prognosis judgment for NSCLC, and can provide experimental evidence for biotherapy of NSCLC.
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