Pontin, a new mutant p53-binding protein, promotes gain-of-function of mutant p53

Genome-wide CRISPR screens identify novel regulators of wild-type and mutant p53 stability

Tumor suppressor p53 (TP53) is frequently mutated in cancer, often resulting not only in loss of its tumor-suppressive function but also acquisition of dominant-negative and even oncogenic gain-of-function traits. While wild-type p53 levels are tightly regulated, mutants are typically stabilized in tumors, which is crucial for their oncogenic properties. Here, we systematically profiled the factors that regulate protein stability of wild-type and mutant p53 using marker-based genome-wide CRISPR screens. Most regulators of wild-type p53 also regulate p53 mutants, except for p53 R337H regulators, which are largely private to this mutant. Mechanistically, FBXO42 emerged as a positive regulator for a subset of p53 mutants, working with CCDC6 to control USP28-mediated mutant p53 stabilization. Additionally, C16orf72/HAPSTR1 negatively regulates both wild-type p53 and all tested mutants. C16orf72/HAPSTR1 is commonly amplified in breast cancer, and its overexpression reduces p53 levels in mouse mammary epithelium leading to accelerated breast cancer. This study offers a network perspective on p53 stability regulation, potentially guiding strategies to reinforce wild-type p53 or target mutant p53 in cancer.

RUVBL1 accelerates tongue squamous cell carcinoma by mediating CRaf/MEK/ERK pathway

RAF/MEK/ERK pathway is frequently activated in tumor. Therefore, this study will investigate the function of RUVBL1 (RAF-binding protein) in tongue squamous cell carcinoma (TSCC). Bioinformatics was performed to identify differentially expressed mRNAs (DE-mRNAs) in TCGA-oral squamous cell carcinoma, GSE13601, and GSE34105 datasets. A total of 672 shared DE-mRNAs were identified in three datasets, and they are regulating metastasis and angiogenesis. Patients with RUVBL1 low expression had high overall survival. Overexpressing RUVBL1 enhanced the viability, wound healing percentage, invasion, sphere formation, angiogenesis, and resistance to cisplatin and 5-fluorouracil in CAL-27 and SCC-4 cells, and the opposite results were obtained by knocking down RUVBL1. Moreover, overexpression of RUVBL1 bolstered tumor growth in vivo. Strikingly, RUVBL1 diminished the phosphorylation of CRAF Ser259, which led to activation of the MEK/ERK pathway. In conclusion, RUVBL1 contributes to the malignant biological behavior of TSCC via activating the CRAF/MEK/ERK pathway. This provides molecular mechanisms and perspectives for targeted therapy of the CRAF/MEK/ERK pathway.

Biomimetic Structure Hydrogel Loaded with Long-Term Storage Platelet-Rich Plasma in Diabetic Wound Repair

Exploring the preparation of multifunctional hydrogels from a bionic perspective is an appealing strategy. Here, a multifunctional hydrogel dressing inspired by the characteristics of porous extracellular matrix produced during Acomys wound healing is prepared. These dressings are printed by digital light processing printing of hydrogels composed of gelatin methacrylate, hyaluronic acid methacrylate, and pretreated platelet-rich plasma (PRP) to shape out triply periodic minimal surface structures, which are freeze-dried for long-term storage. These dressings mimic the porous extracellular matrix of Acomys, while the freeze-drying technique effectively extends the storage duration of PRP viability. Through in vivo and in vitro experiments, the biomimetic dressings developed in this study modulate cell behavior and facilitate wound healing. Consequently, this research offers a novel approach for the advancement of regenerative wound dressings.

CRISPR/Cas9-based application for cancer therapy: Challenges and solutions for non-viral delivery

CRISPR/Cas9 genome editing is a promising therapeutic technique, which makes precise and rapid gene editing technology possible on account of its high sensitivity and efficiency. CRISPR/Cas9 system has been proved to able to effectively disrupt and modify genes, which shows great potential for cancer treatment. Current researches proves that virus vectors are capable of effectively delivering the CRISPR/Cas9 system, but immunogenicity and carcinogenicity caused by virus transmission still trigger serious consequences. Therefore, the greatest challenge of CRISPR/Cas9 for cancer therapy lies on how to deliver it to the target tumor site safely and effectively. Non-viral delivery systems with specific targeting, high loading capacity, and low immune toxicity are more suitable than viral vectors, which limited by uncontrollable side effects. Their medical advances and applications have been widely concerned. Herein, we present the molecule mechanism and different construction strategies of CRISPR/Cas9 system for editing genes at the beginning of this research. Subsequently, several common CRISPR/Cas9 non-viral deliveries for cancer treatment are introduced. Lastly, based on the main factors limiting the delivery efficiency of non-viral vectors proposed in the existing researches and literature, we summarize and discuss the main methods to solve these limitations in the existing tumor treatment system, aiming to introduce further optimization and innovation of the CRISPR/Cas9 non-viral delivery system suitable for cancer treatment.

The ubiquitin ligase TRIM21 regulates mutant p53 accumulation and gain of function in cancer

The tumor suppressor TP53 is the most frequently mutated gene in human cancers. Mutant p53 (mutp53) proteins often accumulate to very high levels in human cancers to promote cancer progression through the gain-of-function (GOF) mechanism. Currently, the mechanism underlying mutp53 accumulation and GOF is incompletely understood. Here, we identified TRIM21 as a critical E3 ubiquitin ligase of mutp53 by screening for specific mutp53-interacting proteins. TRIM21 directly interacted with mutp53 but not WT p53, resulting in ubiquitination and degradation of mutp53 to suppress mutp53 GOF in tumorigenesis. TRIM21 deficiency in cancer cells promoted mutp53 accumulation and GOF in tumorigenesis. Compared with p53R172H knockin mice, which displayed mutp53 accumulation specifically in tumors but not normal tissues, TRIM21 deletion in p53R172H knockin mice resulted in mutp53 accumulation in normal tissues, an earlier tumor onset, and a shortened life span of mice. Furthermore, TRIM21 was frequently downregulated in some human cancers, including colorectal and breast cancers, and low TRIM21 expression was associated with poor prognosis in patients with cancers carrying mutp53. Our results revealed a critical mechanism underlying mutp53 accumulation in cancers and also uncovered an important tumor-suppressive function of TRIM21 and its mechanism in cancers carrying mutp53.

The transcriptional coactivator RUVBL2 regulates Pol II clustering with diverse transcription factors

RNA polymerase II (Pol II) apparatuses are compartmentalized into transcriptional clusters. Whether protein factors control these clusters remains unknown. In this study, we find that the ATPase-associated with diverse cellular activities (AAA + ) ATPase RUVBL2 co-occupies promoters with Pol II and various transcription factors. RUVBL2 interacts with unphosphorylated Pol II in chromatin to promote RPB1 carboxy-terminal domain (CTD) clustering and transcription initiation. Rapid depletion of RUVBL2 leads to a decrease in the number of Pol II clusters and inhibits nascent RNA synthesis, and tethering RUVBL2 to an active promoter enhances Pol II clustering at the promoter. We also identify target genes that are directly linked to the RUVBL2-Pol II axis. Many of these genes are hallmarks of cancers and encode proteins with diverse cellular functions. Our results demonstrate an emerging activity for RUVBL2 in regulating Pol II cluster formation in the nucleus.

RNA polymerase II (Pol II) transcription factories play a central role in gene expression and 3D chromatin organization. Here, the authors demonstrate that RUVBL2 directly regulates Pol II clustering at active gene promoters.

TP53 Gain-of-Function and Non-Gain-of-Function Mutations Are Differentially Associated With Sidedness-Dependent Prognosis in Metastatic Colorectal Cancer

PURPOSE

To examine the association of gain-of-function (GOF) and non-gain-of-function (non-GOF) TP53 mutations with prognosis of metastatic right-sided (RCC) versus left-sided colorectal cancer (LCC).

METHODS

This cohort study included patients with metastatic colorectal cancer (CRC) who had next-generation sequencing performed from November 2017 to January 2021. We defined R175H, R248W, R248Q, R249S, R273H, R273L, and R282W as GOF and all other mutp53 as non-GOF. We used Cox regression modeling to examine the association between GOF and non-GOF mutp53 and overall survival (OS), adjusting for age, sex, ethnicity, performance status, Charlson comorbidity index and receipt of chemotherapy.

RESULTS

Of total 1,043 patients, 735 had tumors with mutp53 and 308 had wild-type p53 (wtp53). GOF was associated with worse OS than non-GOF mutp53 only in LCC (hazard ratio [HR] = 1.66 [95% CI, 1.20 to 2.29]), but not in RCC (HR = 0.79 [95% CI, 0.49 to 1.26]). Importantly, RCC was associated with worse OS than LCC only in the subset of patients whose CRC carried non-GOF (HR = 1.76 [95% CI, 1.30 to 2.39]), but not GOF mutp53 (HR = 0.92 [95% CI, 0.55 to 1.53]) or wtp53 (HR = 0.88 [95% CI, 0.60 to 1.28]). These associations were largely unchanged after also adjusting for RAS, BRAF, and PIK3CA mutations, and microsatellite instability-high.

CONCLUSION

Poorer survival of patients with metastatic RCC versus LCC appeared to be restricted to the subset with non-GOF mutp53, whereas GOF versus non-GOF mutp53 was associated with poorer survival only among patients with LCC. This approach of collectively classifying mutp53 into GOF and non-GOF provides new insight for prognostic stratification and for understanding the mechanism of sidedness-dependent prognosis. If confirmed, future CRC clinical trials may benefit from incorporating this approach.

Identification of limonoids from Walsura yunnanensis and evaluation of their cytotoxicity against cancer cell lines

Three new limonoids, walsurauias A-C (1-3), along with four known ones, were isolated from the leaves and twigs of Walsura yunnanensis C. Y. Wu. Their structures were determined on the basis of comprehensive spectroscopic data analysis. The new limonoids were screened for their cytotoxic activity (IC₅₀ 0.81-5.73 μM) against four human cancer cell lines, including A549, HepG2, HCT116 p21KO and CNE-2. And α,β-unsaturated ketone moieties in rings A and B are essential for their cytotoxic activity. Selected compounds were further investigated. Compounds 1-3 effectively induced G2/M cell cycle arrest and apoptosis in a dose-dependent manner in cancer cells. In addition, compounds 1-3 inhibited the colony formation and compounds 2 and 3 suppressed the migration of cancer cells.

Δ133p53β isoform pro-invasive activity is regulated through an aggregation-dependent mechanism in cancer cells

The p53 isoform, Δ133p53β, is critical in promoting cancer. Here we report that Δ133p53β activity is regulated through an aggregation-dependent mechanism. Δ133p53β aggregates were observed in cancer cells and tumour biopsies. The Δ133p53β aggregation depends on association with interacting partners including p63 family members or the CCT chaperone complex. Depletion of the CCT complex promotes accumulation of Δ133p53β aggregates and loss of Δ133p53β dependent cancer cell invasion. In contrast, association with p63 family members recruits Δ133p53β from aggregates increasing its intracellular mobility. Our study reveals novel mechanisms of cancer progression for p53 isoforms which are regulated through sequestration in aggregates and recruitment upon association with specific partners like p63 isoforms or CCT chaperone complex, that critically influence cancer cell features like EMT, migration and invasion.

Gain-of-function mutant p53 in cancer progression and therapy

p53 is a key tumor suppressor, and loss of p53 function is frequently a prerequisite for cancer development. The p53 gene is the most frequently mutated gene in human cancers; p53 mutations occur in >50% of all human cancers and in almost every type of human cancers. Most of p53 mutations in cancers are missense mutations, which produce the full-length mutant p53 (mutp53) protein with only one amino acid difference from wild-type p53 protein. In addition to loss of the tumor-suppressive function of wild-type p53, many mutp53 proteins acquire new oncogenic activities independently of wild-type p53 to promote cancer progression, termed gain-of-function (GOF). Mutp53 protein often accumulates to very high levels in cancer cells, which is critical for its GOF. Given the high mutation frequency of the p53 gene and the GOF activities of mutp53 in cancer, therapies targeting mutp53 have attracted great interest. Further understanding the mechanisms underlying mutp53 protein accumulation and GOF will help develop effective therapies treating human cancers containing mutp53. In this review, we summarize the recent advances in the studies on mutp53 regulation and GOF as well as therapies targeting mutp53 in human cancers.

Pontin Functions as A Transcriptional Co-activator for Retinoic Acid-induced HOX Gene Expression

Pontin is a AAA+ ATPase protein that has functions in various biological contexts including gene transcription regulation, chromatin remodeling, DNA damage sensing and repair, as well as assembly of protein and ribonucleoprotein complexes. Pontin is known to regulate the transcription of several important signaling pathways, including Wnt signaling. However, its role in early embryonic signaling regulation remains unclear. Retinoic acid (RA) signaling plays a central role in vertebrate development. Using an in vivo biotin tagging technology, we mapped the genome-wide binding pattern of Pontin before and after RA-induced differentiation in the pluripotent embryo carcinoma cell line NTERA-2. Biotin ChIP-seq revealed significant changes in genome-wide Pontin binding sites upon RA stimulation. We also identified a substantial amount of overlapping binding peaks between Pontin and RARα, especially on all of the HOX gene loci (A-D clusters). Pontin knockdown experiments showed that its chromatin binding at the HOX gene clusters is required for RA-induced HOX gene expression. Furthermore, we performed Global Run-On sequencing (GRO-seq) to map de novo transcripts genome-wide and found that Pontin knockdown significantly diminished nascent HOX gene transcripts, indicating that Pontin regulates HOX gene expression at the transcriptional level. Finally, proteomic analysis demonstrated that Pontin associates with chromatin organization/remodeling complexes and various other functional complexes. Altogether, we have demonstrated that Pontin is a critical transcriptional co-activator for RA-induced HOX gene activation.

The Role of p53 Signaling in Colorectal Cancer

The transcription factor p53 functions as a critical tumor suppressor by orchestrating a plethora of cellular responses such as DNA repair, cell cycle arrest, cellular senescence, cell death, cell differentiation, and metabolism. In unstressed cells, p53 levels are kept low due to its polyubiquitination by the E3 ubiquitin ligase MDM2. In response to various stress signals, including DNA damage and aberrant growth signals, the interaction between p53 and MDM2 is blocked and p53 becomes stabilized, allowing p53 to regulate a diverse set of cellular responses mainly through the transactivation of its target genes. The outcome of p53 activation is controlled by its dynamics, its interactions with other proteins, and post-translational modifications. Due to its involvement in several tumor-suppressing pathways, p53 function is frequently impaired in human cancers. In colorectal cancer (CRC), the TP53 gene is mutated in 43% of tumors, and the remaining tumors often have compromised p53 functioning because of alterations in the genes encoding proteins involved in p53 regulation, such as ATM (13%) or DNA-PKcs (11%). TP53 mutations in CRC are usually missense mutations that impair wild-type p53 function (loss-of-function) and that even might provide neo-morphic (gain-of-function) activities such as promoting cancer cell stemness, cell proliferation, invasion, and metastasis, thereby promoting cancer progression. Although the first compounds targeting p53 are in clinical trials, a better understanding of wild-type and mutant p53 functions will likely pave the way for novel CRC therapies.

Identification and characterization of R2TP in the development of oral squamous cell carcinoma

R2TP is a well-conserved molecular chaperone complex, composed of Pontin, Reptin, RPAP3, and PIH1D, in eukaryotes. Recent studies have suggested an involvement of R2TP in cancer development. However, it remains unclear if it is related to the development of oral squamous cell carcinoma (OSCC), which is the most common type of oral cancer. Here, we identify and investigate the function of R2TP in OSCC development. Immunohistochemical analysis reveals that all of the R2TP components are strongly expressed in normal oral epithelia and OSCC tissues, where actively proliferating cells are abundant. Co-immunoprecipitation assay identifies that R2TP components form a protein complex in OSCC-derived HSC4-cells. Knockdown experiments show that all R2TP components, except for RPAP3, are required for the cell proliferation and migration of HSC-4 cells. Furthermore, we reveal that Pontin contributes to a gain-of-function (GOF) activity of mutp53-R248Q in HSC-4 cells by regulating phosphorylation levels of mutp53 at Ser15 and Ser46. To our knowledge, this study is the first to report the functional involvement of R2TP and its components in the malignant characteristics of OSCC cells.

Non-canonical roles of canonical telomere binding proteins in cancers

Reactivation of telomerase is a major hallmark observed in 90% of all cancers. Yet paradoxically, enhanced telomerase activity does not correlate with telomere length and cancers often possess short telomeres; suggestive of supplementary non-canonical roles that telomerase might play in the development of cancer. Moreover, studies have shown that aberrant expression of shelterin proteins coupled with their release from shortening telomeres can further promote cancer by mechanisms independent of their telomeric role. While targeting telomerase activity appears to be an attractive therapeutic option, this approach has failed in clinical trials due to undesirable cytotoxic effects on stem cells. To circumvent this concern, an alternative strategy could be to target the molecules involved in the non-canonical functions of telomeric proteins. In this review, we will focus on emerging evidence that has demonstrated the non-canonical roles of telomeric proteins and their impact on tumorigenesis. Furthermore, we aim to address current knowledge gaps in telomeric protein functions and propose future research approaches that can be undertaken to achieve this.

Astaxanthin Reduces Stemness Markers in BT20 and T47D Breast Cancer Stem Cells by Inhibiting Expression of Pontin and Mutant p53

Astaxanthin (AST) is a product made from marine organisms that has been used as an anti-cancer supplement. It reduces pontin expression and induces apoptosis in SKBR3, a breast cancer cell line. Using Western blotting and qRT-PCR analyses, this study revealed that in the T47D and BT20 breast cancer cell lines, AST inhibits expression of pontin and mutp53, as well as the Oct4 and Nanog cancer stem cell (CSC) stemness genes. In addition, we explored the mechanism by which AST eradicates breast cancer cells using pontin siRNAs. Pontin knockdown by pontin siRNA reduced proliferation, Oct4 and Nanog expression, colony and spheroid formation, and migration and invasion abilities in breast cancer cells. In addition, reductions in Oct4, Nanog, and mutp53 expression following rottlerin treatment confirmed the role of pontin in these cells. Therefore, pontin may play a central role in the regulation of CSC properties and in cell proliferation following AST treatment. Taken together, these findings demonstrate that AST can repress CSC stemness genes in breast cancer cells, which implies that AST therapy could be used to improve the efficacy of other anti-cancer therapies against breast cancer cells.

Astaxanthin Modulates Apoptotic Molecules to Induce Death of SKBR3 Breast Cancer Cells

Astaxanthin (AST) is related to apoptosis but the details of the mechanism of how AST makes apoptosis is not clear. The present study investigated apoptotic effects of AST to SKBR3, a breast cancer cell line in detail. Cell viability assay showed cellular proliferation and morphological changes of the cells were observed under AST treatment. FACS analysis indicated that AST blocked cell cycle progression at G0/G1, suppressed proliferation dose-dependently, and induced apoptosis of the cells. The apoptosis of the cells by AST was further demonstrated through the decreased expression level of mutp53 and cleaved a PARP-1 fragment, respectively. In addition, AST induced the intrinsic apoptosis of the cells by activation of Bax/Bcl2, cleaved caspase-3, and cleaved caspase-9 as well as the phosphorylation of ERK1/2, JNK, and p38. Furthermore, AST decreased production of intracellular reactive oxygen species as well as modulated expressions of superoxide dismutases and Pontin, an anti-apoptotic factor. Co-immunoprecipitation assay revealed AST reduced interaction between Pontin and mutant p53. Taken together, these studies proved that AST regulates the expression of apoptotic molecules to induce intrinsic apoptosis of the cells, suggesting AST therapy might provide an alternative for improving the efficacies of other anti-cancer therapies for breast cancer.

Gain-of-Function Mutant p53: All the Roads Lead to Tumorigenesis

The p53 protein is mutated in about 50% of human cancers. Aside from losing the tumor-suppressive functions of the wild-type form, mutant p53 proteins often acquire inherent, novel oncogenic functions, a phenomenon termed mutant p53 gain-of-function (GOF). A growing body of evidence suggests that these pro-oncogenic functions of mutant p53 proteins are mediated by affecting the transcription of various genes, as well as by protein-protein interactions with transcription factors and other effectors. In the current review, we discuss the various GOF effects of mutant p53, and how it may serve as a central node in a network of genes and proteins, which, altogether, promote the tumorigenic process. Finally, we discuss mechanisms by which "Mother Nature" tries to abrogate the pro-oncogenic functions of mutant p53. Thus, we suggest that targeting mutant p53, via its reactivation to the wild-type form, may serve as a promising therapeutic strategy for many cancers that harbor mutant p53. Not only will this strategy abrogate mutant p53 GOF, but it will also restore WT p53 tumor-suppressive functions.

The Emerging Roles of ATP-Dependent Chromatin Remodeling Complexes in Pancreatic Cancer

Pancreatic cancer is an aggressive cancer with low survival rates. Genetic and epigenetic dysregulation has been associated with the initiation and progression of pancreatic tumors. Multiple studies have pointed to the involvement of aberrant chromatin modifications in driving tumor behavior. ATP-dependent chromatin remodeling complexes regulate chromatin structure and have critical roles in stem cell maintenance, development, and cancer. Frequent mutations and chromosomal aberrations in the genes associated with subunits of the ATP-dependent chromatin remodeling complexes have been detected in different cancer types. In this review, we summarize the current literature on the genomic alterations and mechanistic studies of the ATP-dependent chromatin remodeling complexes in pancreatic cancer. Our review is focused on the four main subfamilies: SWItch/sucrose non-fermentable (SWI/SNF), imitation SWI (ISWI), chromodomain-helicase DNA-binding protein (CHD), and INOsitol-requiring mutant 80 (INO80). Finally, we discuss potential novel treatment options that use small molecules to target these complexes.

Wild-type p53 oligomerizes more efficiently than p53 hot-spot mutants and overcomes mutant p53 gain-of-function via a "dominant-positive" mechanism

Human p53 protein acts as a transcription factor predominantly in a tetrameric form. Single residue changes, caused by hot-spot mutations of the TP53 gene in human cancer, transform wild-type (wt) p53 tumor suppressor proteins into potent oncoproteins - with gain-of-function, tumor-promoting activity. Oligomerization of p53 allows for a direct interplay between wt and mutant p53 proteins if both are present in the same cells - where a mutant p53's dominant-negative effect known to inactivate wt p53, co-exists with an opposite mechanism - a "dominant-positive" suppression of the mutant p53's gain-of-function activity by wt p53. In this study we determine the oligomerization efficiency of wt and mutant p53 in living cells using FRET-based assays and describe wt p53 to be more efficient than mutant p53 in entering p53 oligomers. The biased p53 oligomerization helps to interpret earlier reports of a low efficiency of the wt p53 inactivation via the dominant-negative effect, while it also implies that the "dominant-positive" effect may be more pronounced. Indeed, we show that at similar wt:mutant p53 concentrations in cells - the mutant p53 gain-of-function stimulation of gene transcription and cell migration is more efficiently inhibited than the wt p53's tumor-suppressive transactivation and suppression of cell migration. These results suggest that the frequent mutant p53 accumulation in human tumor cells does not only directly strengthen its gain-of-function activity, but also protects the oncogenic p53 mutants from the functional dominance of wt p53.

The p53 Family in Brain Disease

SIGNIFICANCE

The p53 family of transcription factors, including p53, p63, and p73, plays key roles in both biological and pathological processes, including cancer and neural development. Recent Advances: In recent years, a growing body of evidence has indicated that the entire p53 family is involved in the regulation of the central nervous system (CNS) functions as well as in the pathogenesis of several neurological disorders. Mechanistically, the p53 proteins control neuronal cell fate, terminal differentiation, and survival, via a complex interplay among the family members.

CRITICAL ISSUES

In this article, we discuss the involvement of the p53 family in neurobiology and in pathological conditions affecting the CNS, including neuroinflammation.

FUTURE DIRECTIONS

Understanding the molecular mechanism(s) underlying the function of the p53 family could improve our general knowledge of the pathogenesis of brain disorders and potentially pave the road for new therapeutic intervention. Antioxid. Redox Signal. 29, 1-14.

Complexes formed by mutant p53 and their roles in breast cancer

Breast cancer is the most frequently diagnosed malignancy in women, and mutations in the tumor suppressor p53 are commonly detected in the most aggressive subtypes. The majority of TP53 gene alterations are missense substitutions, leading to expression of mutant forms of the p53 protein that are frequently detected at high levels in cancer cells. P53 mutants not only lose the physiological tumor-suppressive activity of the wild-type p53 protein but also acquire novel powerful oncogenic functions, referred to as gain of function, that may actively confer a selective advantage during tumor progression. Some of the best-characterized oncogenic activities of mutant p53 are mediated by its ability to form aberrant protein complexes with other transcription factors or proteins not directly related to gene transcription. The set of cellular proteins available to interact with mutant p53 is dependent on cell type and extensively affected by environmental signals, so the prognostic impact of p53 mutation is complex. Specific functional interactions of mutant p53 can profoundly impact homeostasis of breast cancer cells, reprogramming gene expression in response to specific extracellular inputs or cell-intrinsic conditions. The list of protein complexes involving mutant p53 in breast cancer is continuously growing, as is the number of oncogenic phenotypes in which they could be involved. In consideration of the functional impact of such complexes, key interactions of mutant p53 may be exploited as potential targets for development of therapies aimed at defusing the oncogenic potential of p53 mutation.

Pontin Acts as a Potential Biomarker for Poor Clinical Outcome and Promotes Tumor Invasion in Hilar Cholangiocarcinoma

Hilar cholangiocarcinoma (HC) is a devastating malignancy that carries a poor overall prognosis. As a member of the AAA+ superfamily, Pontin becomes highly expressed in several malignant tumors, which contributes to tumor progression and influences tumor prognosis. In our research, Pontin expression in tumor specimens resected from 86 HC patients was detected by immunohistochemistry. Interestingly, high expression of Pontin was significantly associated with lymph node metastasis (p = 0.011) and tumor node metastasis (TNM) stage (p = 0.005). The Kaplan–Meier overall survival rate and multivariate analyses were performed to evaluate the prognosis of patients with HC. Patients with high Pontin expression had significantly poorer overall survival outcomes. Multivariate analyses found that Pontin was an independent prognostic factor (p = 0.001). Moreover, bioinformatics analysis confirmed the increase in Pontin mRNA expression levels in cholangiocarcinoma tissues. In addition, in vitro experiments showed that Pontin expression was inhibited at the mRNA as well as protein levels after transfection with Pontin siRNA in human cholangiocarcinoma cell lines. Moreover, significant suppression of cell invasion was observed after the downregulation of Pontin. Taken together, the present study suggested that Pontin could act as a potential prognostic predictor, which might be a new valuable molecular candidate for the prevention and treatment of HC.

Impact of RUNX2 on drug-resistant human pancreatic cancer cells with p53 mutations

Background

Despite the remarkable advances in the early diagnosis and treatment, overall 5-year survival rate of patients with pancreatic cancer is less than 10%. Gemcitabine (GEM), a cytidine nucleoside analogue and ribonucleotide reductase inhibitor, is a primary option for patients with advanced pancreatic cancer; however, its clinical efficacy is extremely limited. This unfavorable clinical outcome of pancreatic cancer patients is at least in part attributable to their poor response to anti-cancer drugs such as GEM. Thus, it is urgent to understand the precise molecular basis behind the drug-resistant property of pancreatic cancer and also to develop a novel strategy to overcome this deadly disease.

Review

Accumulating evidence strongly suggests that p53 mutations contribute to the acquisition and/or maintenance of drug-resistant property of pancreatic cancer. Indeed, certain p53 mutants render pancreatic cancer cells much more resistant to GEM, implying that p53 mutation is one of the critical determinants of GEM sensitivity. Intriguingly, runt-related transcription factor 2 (RUNX2) is expressed at higher level in numerous human cancers such as pancreatic cancer and osteosarcoma, indicating that, in addition to its pro-osteogenic role, RUNX2 has a pro-oncogenic potential. Moreover, a growing body of evidence implies that a variety of miRNAs suppress malignant phenotypes of pancreatic cancer cells including drug resistance through the down-regulation of RUNX2. Recently, we have found for the first time that forced depletion of RUNX2 significantly increases GEM sensitivity of p53-null as well as p53-mutated pancreatic cancer cells through the stimulation of p53 family TAp63/TAp73-dependent cell death pathway.

Conclusions

Together, it is likely that RUNX2 is one of the promising molecular targets for the treatment of the patients with pancreatic cancer regardless of their p53 status. In this review article, we will discuss how to overcome the serious drug-resistant phenotype of pancreatic cancer.

Parkin targets HIF-1α for ubiquitination and degradation to inhibit breast tumor progression

Mutations in E3 ubiquitin ligase Parkin have been linked to familial Parkinson’s disease. Accumulating evidence suggests that Parkin is a tumor suppressor, but the underlying mechanism is poorly understood. Here we show that Parkin is an E3 ubiquitin ligase for hypoxia-inducible factor 1α (HIF-1α). Parkin interacts with HIF-1α and promotes HIF-1α degradation through ubiquitination, which in turn inhibits metastasis of breast cancer cells. Parkin downregulation in breast cancer cells promotes metastasis, which can be inhibited by targeting HIF-1α with RNA interference or the small-molecule inhibitor YC-1. We further identify lysine 477 (K477) of HIF-1α as a major ubiquitination site for Parkin. K477R HIF-1α mutation and specific cancer-associated Parkin mutations largely abolish the functions of Parkin to ubiquitinate HIF-1α and inhibit cancer metastasis. Importantly, Parkin expression is inversely correlated with HIF-1α expression and metastasis in breast cancer. Our results reveal an important mechanism for Parkin in tumor suppression and HIF-1α regulation.

Parkin is an E3 ubiquitin ligase involved in Parkinson’s disease. Parkin has also been linked to cancer suppression but the mechanisms are unclear. Here the authors show that Parkin regulates HIF-1α through ubiquitin-dependent degradation, thus inhibiting metastasis of breast cancer cells.

Gain-of-function mutant p53 activates small GTPase Rac1 through SUMOylation to promote tumor progression

Here, Yue et al. investigated the mechanisms underlying p53 gain-of-function (GOF) mutations and found that mutant p53 activates small GTPase Rac1 as a critical mechanism for mutant p53 GOF to promote tumor progression. Their findings provide insight into a new mechanism for Rac1 activation in tumors and show that activation of Rac1 is an unidentified and critical mechanism for mutant p53 GOF in tumorigenesis.

Tumor suppressor p53 is frequently mutated in human cancer. Mutant p53 often promotes tumor progression through gain-of-function (GOF) mechanisms. However, the mechanisms underlying mutant p53 GOF are not well understood. In this study, we found that mutant p53 activates small GTPase Rac1 as a critical mechanism for mutant p53 GOF to promote tumor progression. Mechanistically, mutant p53 interacts with Rac1 and inhibits its interaction with SUMO-specific protease 1 (SENP1), which in turn inhibits SENP1-mediated de-SUMOylation of Rac1 to activate Rac1. Targeting Rac1 signaling by RNAi, expression of the dominant-negative Rac1 (Rac1 DN), or the specific Rac1 inhibitor NSC23766 greatly inhibits mutant p53 GOF in promoting tumor growth and metastasis. Furthermore, mutant p53 expression is associated with enhanced Rac1 activity in clinical tumor samples. These results uncover a new mechanism for Rac1 activation in tumors and, most importantly, reveal that activation of Rac1 is an unidentified and critical mechanism for mutant p53 GOF in tumorigenesis, which could be targeted for therapy in tumors containing mutant p53.

The Role of Pontin and Reptin in Cellular Physiology and Cancer Etiology

Pontin (RUVBL1, TIP49, TIP49a, Rvb1) and Reptin (RUVBL2, TIP48, TIP49b, Rvb2) are highly conserved ATPases of the AAA+ (ATPases Associated with various cellular Activities) superfamily and are involved in various cellular processes that are important for oncogenesis. First identified as being upregulated in hepatocellular carcinoma and colorectal cancer, their overexpression has since been shown in multiple cancer types such as breast, lung, gastric, esophageal, pancreatic, kidney, bladder as well as lymphatic, and leukemic cancers. However, their exact functions are still quite unknown as they interact with many molecular complexes with vastly different downstream effectors. Within the nucleus, Pontin and Reptin participate in the TIP60 and INO80 complexes important for chromatin remodeling. Although not transcription factors themselves, Pontin and Reptin modulate the transcriptional activities of bona fide proto-oncogenes such as MYC and β-catenin. They associate with proteins involved in DNA damage repair such as PIKK complexes as well as with the core complex of Fanconi anemia pathway. They have also been shown to be important for cell cycle progression, being involved in assembly of telomerase, mitotic spindle, RNA polymerase II, and snoRNPs. When the two ATPases localize to the cytoplasm, they were reported to promote cancer cell invasion and metastasis. Due to their various roles in carcinogenesis, it is not surprising that Pontin and Reptin are proving to be important biomarkers for diagnosis and prognosis of various cancers. They are also current targets for the development of new therapeutic anticancer drugs.

Mutant p53 in Cancer: Accumulation, Gain-of-Function, and Therapy

Tumor suppressor p53 plays a central role in tumor suppression. p53 is the most frequently mutated gene in human cancer, and over half of human cancers contain p53 mutations. Majority of p53 mutations in cancer are missense mutations, leading to the expression of full-length mutant p53 (mutp53) protein. While the critical role of wild-type p53 in tumor suppression has been firmly established, mounting evidence has demonstrated that many tumor-associated mutp53 proteins not only lose the tumor-suppressive function of wild-type p53 but also gain new activities to promote tumorigenesis independently of wild-type p53, termed gain-of-function. Mutant p53 protein often accumulates to very high levels in tumors, contributing to malignant progression. Recently, mutp53 has become an attractive target for cancer therapy. Further understanding of the mechanisms underlying mutp53 protein accumulation and gain-of-function will accelerate the development of targeted therapies for human cancer harboring mutp53. In this review, we summarize the recent advances in the studies on mutp53 protein accumulation and gain-of-function and targeted therapies for mutp53 in human cancer.

RUVBL1-ITFG1 interaction is required for collective invasion in breast cancer

BACKGROUND

The mechanisms of breast cancer collective invasion are poorly understood limiting the metastasis therapy. The ATPase RUVBL1 is frequently overexpressed in various cancers and plays a crucial role in oncogenic process. We further investigated the role of RUVBL1 in promoting collective invasion and uncovered that targeting RUVBL1 could inhibit metastatic progression.

METHODS

The expression levels of RUVBL1 and ITFG1 were examined by Western blot and qRT-PCR. Co-localization and interaction of RUVBL1 and ITFG1 were determined by immunofluorescence and co-immunoprecipitation. The invasive ability was examined by transwell assay and microfluidic assay. The metastatic and tumorigenic abilities of breast cancer cells were revealed in BALB/c nude mice by xenograft and tail vein injection.

RESULTS

ATPase RUVBL1 is highly expressed in breast cancer and predicts the poor prognosis. Elevated expression of RUVBL1 is found in high metastatic breast cancer cells. Silencing RUVBL1 suppresses cancer cell expansion and invasion in vitro and in vivo. RUVBL1 interacts with a conserved transmembrane protein ITFG1 in cytoplasm and plasma membrane to promote the collective invasion. Using a microfluidic model, we demonstrated that silencing RUVBL1 or ITFG1 individually compromises collective invasion of breast cancer cells.

CONCLUSION

RUVBL1 is a vital regulator for collective invasion. The interaction between RUVBL1 and ITFG1 is required for breast cancer cell collective invasion and progression.

GENERAL SIGNIFICANCE

Targeting collective invasion promoted by RUVBL1-ITFG1 complex provides a novel therapeutic strategy to improve the prognosis of invasive breast cancer.

p53: Multiple Facets of a Rubik's Cube

The p53 tumor suppressor has been studied for decades, and still there are many questions left unanswered. In this review, we first describe the current understanding of the wild-type p53 functions that determine cell survival or death, and regulation of the protein, with a particular focus on the negative regulators, the murine double minute family of proteins. We also summarize tissue-, stress-, and age-specific p53 activities and the potential underlying mechanisms. Among all p53 gene alterations identified in human cancers, p53 missense mutations predominate, suggesting an inherent biological advantage. Numerous gain-of-function activities of mutant p53 in different model systems and contexts have been identified. The emerging theme is that mutant p53, which retains a potent transcriptional activation domain, also retains the ability to modify gene transcription, albeit indirectly. Lastly, because mutant p53 stability is necessary for its gain of function, we summarize the mechanisms through which mutant p53 is specifically stabilized. A deeper understanding of the multiple pathways that impinge upon wild-type and mutant p53 activities and how these, in turn, regulate cell behavior will help identify vulnerabilities and therapeutic opportunities.

Novel targets and interaction partners of mutant p53 Gain-Of-Function

In many human cancers p53 expression is lost or a mutant p53 protein is expressed. Over the past 15 years it has become apparent that a large number of these mutant p53 proteins have lost wild type function, but more importantly have gained functions that promote tumorigenesis and drive chemo-resistance, invasion and metastasis. Many researchers have investigated the underlying mechanisms of these Gain-Of-Functions (GOFs) and it has become apparent that many of these functions are the result of mutant p53 hijacking other transcription factors. In this review, we summarize the latest research on p53 GOF and categorize these in light of the hallmarks of cancer as presented by Hannahan and Weinberg.

Differential regulated microRNA by wild type and mutant p53 in induced pluripotent stem cells

The tumour suppressor p53 plays an important role in somatic cell reprogramming. While wild-type p53 reduces reprogramming efficiency, mutant p53 exerts a gain of function activity that leads to increased reprogramming efficiency. Furthermore, induced pluripotent stem cells expressing mutant p53 lose their pluripotency in vivo and form malignant tumours when injected in mice. It is therefore of great interest to identify targets of p53 (wild type and mutant) that are responsible for this phenotype during reprogramming, as these could be exploited for therapeutic use, that is, formation of induced pluripotent stem cells with high reprogramming efficiency, but no oncogenic potential. Here we studied the transcriptional changes of microRNA in a series of mouse embryonic fibroblasts that have undergone transition to induced pluripotent stem cells with wild type, knock out or mutant p53 status in order to identify microRNAs whose expression during reprogramming is dependent on p53. We identified a number of microRNAs, with known functions in differentiation and carcinogenesis, the expression of which was dependent on the p53 status of the cells. Furthermore, we detected several uncharacterised microRNAs that were regulated differentially in the different p53 backgrounds, suggesting a novel role of these microRNAs in reprogramming and pluripotency.

A novel mutant p53 binding partner BAG5 stabilizes mutant p53 and promotes mutant p53 GOFs in tumorigenesis

Tumor suppressor p53 is the most frequently mutated gene in human tumors. Many tumor-associated mutant p53 (mutp53) proteins gain new tumor-promoting activities, including increased proliferation, metastasis and chemoresistance of tumor cells, which are defined as gain-of-functions (GOFs). Mutp53 proteins often accumulate at high levels in human tumors, which is important for mutp53 to exert their GOFs. The mechanism underlying mutp53 proteins accumulation in tumors is not fully understood. Here, we report that BAG5, a member of Bcl-2-associated athanogene (BAG) family proteins, promotes mutp53 accumulation in tumors, which in turn enhances mutp53 GOFs. Mechanistically, BAG5 interacts with mutp53 proteins to protect mutp53 from ubiquitination and degradation by E3 ubiquitin ligases MDM2 and CHIP, which in turn promotes mutp53 protein accumulation and therefore GOFs in promoting cell proliferation, tumor growth, cell migration and chemoresistance. BAG5 is frequently overexpressed in many human tumors and the overexpression of BAG5 is associated with poor prognosis of cancer patients. Altogether, this study revealed that inhibition of mutp53 degradation by BAG5 is a novel and critical mechanism underlying mutp53 protein accumulation and GOFs in cancer. Furthermore, our results also uncovered that promoting mutp53 accumulation and GOFs is a novel mechanism of BAG5 in tumorigenesis.

Glutaminase 2 is a novel negative regulator of small GTPase Rac1 and mediates p53 function in suppressing metastasis

Glutaminase (GLS) isoenzymes GLS1 and GLS2 are key enzymes for glutamine metabolism. Interestingly, GLS1 and GLS2 display contrasting functions in tumorigenesis with elusive mechanism; GLS1 promotes tumorigenesis, whereas GLS2 exhibits a tumor-suppressive function. In this study, we found that GLS2 but not GLS1 binds to small GTPase Rac1 and inhibits its interaction with Rac1 activators guanine-nucleotide exchange factors, which in turn inhibits Rac1 to suppress cancer metastasis. This function of GLS2 is independent of GLS2 glutaminase activity. Furthermore, decreased GLS2 expression is associated with enhanced metastasis in human cancer. As a p53 target, GLS2 mediates p53's function in metastasis suppression through inhibiting Rac1. In summary, our results reveal that GLS2 is a novel negative regulator of Rac1, and uncover a novel function and mechanism whereby GLS2 suppresses metastasis. Our results also elucidate a novel mechanism that contributes to the contrasting functions of GLS1 and GLS2 in tumorigenesis.

How do oncoprotein mutations rewire protein-protein interaction networks?

The acquisition of mutations that activate oncogenes or inactivate tumor suppressors is a primary feature of most cancers. Mutations that directly alter protein sequence and structure drive the development of tumors through aberrant expression and modification of proteins, in many cases directly impacting components of signal transduction pathways and cellular architecture. Cancer-associated mutations may have direct or indirect effects on proteins and their interactions and while the effects of mutations on signaling pathways have been widely studied, how mutations alter underlying protein-protein interaction networks is much less well understood. Systematic mapping of oncoprotein protein interactions using proteomics techniques as well as computational network analyses is revealing how oncoprotein mutations perturb protein-protein interaction networks and drive the cancer phenotype.

BAG2 promotes tumorigenesis through enhancing mutant p53 protein levels and function

Tumor suppressor p53 is the most frequently mutated gene in tumors. Many mutant p53 (mutp53) proteins promote tumorigenesis through the gain-of-function (GOF) mechanism. Mutp53 proteins often accumulate to high levels in tumors, which is critical for mutp53 GOF. Its underlying mechanism is poorly understood. Here, we found that BAG2, a protein of Bcl-2 associated athanogene (BAG) family, promotes mutp53 accumulation and GOF in tumors. Mechanistically, BAG2 binds to mutp53 and translocates to the nucleus to inhibit the MDM2-mutp53 interaction, and MDM2-mediated ubiquitination and degradation of mutp53. Thus, BAG2 promotes mutp53 accumulation and GOF in tumor growth, metastasis and chemoresistance. BAG2 is frequently overexpressed in tumors. BAG2 overexpression is associated with poor prognosis in patients and mutp53 accumulation in tumors. These findings revealed a novel and important mechanism for mutp53 accumulation and GOF in tumors, and also uncovered an important role of BAG2 in tumorigenesis through promoting mutp53 accumulation and GOF.

Pontin, a novel interactor of mutant p53 that promotes mutant p53 gain of function

Many tumor-associated mutant p53 proteins gain new activities to promote tumorigenesis, which is termed as gain of function of mutant p53 (GOF). Currently, the mechanisms of mutant p53 GOF remain elusive. We recently identified the AAA+ ATPase pontin as a critical regulator of mutant p53 GOF, thus providing a novel mechanism for mutant p53 GOF.