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

S-Nitrosylation of Septin2 Exacerbates Aortic Aneurysm and Dissection by Coupling the TIAM1-RAC1 Axis in Macrophages

BACKGROUND

S-Nitrosylation (SNO), a prototypic redox-based posttranslational modification, is involved in cardiovascular disease. Aortic aneurysm and dissection are high-risk cardiovascular diseases without an effective cure. The aim of this study was to determine the role of SNO of Septin2 in macrophages in aortic aneurysm and dissection.

METHODS

Biotin-switch assay combined with liquid chromatography-tandem mass spectrometry was performed to identify the S-nitrosylated proteins in aortic tissue from both patients undergoing surgery for aortic dissection and Apoe-/- mice infused with angiotensin II. Angiotensin II-induced aortic aneurysm model and β-aminopropionitrile-induced aortic aneurysm and dissection model were used to determine the role of SNO of Septin2 (SNO-Septin2) in aortic aneurysm and dissection development. RNA-sequencing analysis was performed to recapitulate possible changes in the transcriptome profile of SNO-Septin2 in macrophages in aortic aneurysm and dissection. Liquid chromatography-tandem mass spectrometry and coimmunoprecipitation were used to uncover the TIAM1-RAC1 (Ras-related C3 botulinum toxin substrate 1) axis as the downstream target of SNO-Septin2. Both R-Ketorolac and NSC23766 treatments were used to inhibit the TIAM1-RAC1 axis.

RESULTS

Septin2 was identified S-nitrosylated at cysteine 111 (Cys111) in both aortic tissue from patients undergoing surgery for aortic dissection and Apoe-/- mice infused with Angiotensin II. SNO-Septin2 was demonstrated driving the development of aortic aneurysm and dissection. By RNA-sequencing, SNO-Septin2 in macrophages was demonstrated to exacerbate vascular inflammation and extracellular matrix degradation in aortic aneurysm. Next, TIAM1 (T lymphoma invasion and metastasis-inducing protein 1) was identified as a SNO-Septin2 target protein. Mechanistically, compared with unmodified Septin2, SNO-Septin2 reduced its interaction with TIAM1 and activated the TIAM1-RAC1 axis and consequent nuclear factor-κB signaling pathway, resulting in stronger inflammation and extracellular matrix degradation mediated by macrophages. Consistently, both R-Ketorolac and NSC23766 treatments protected against aortic aneurysm and dissection by inhibiting the TIAM1-RAC1 axis.

CONCLUSIONS

SNO-Septin2 drives aortic aneurysm and dissection through coupling the TIAM1-RAC1 axis in macrophages and activating the nuclear factor-κB signaling pathway-dependent inflammation and extracellular matrix degradation. Pharmacological blockade of RAC1 by R-Ketorolac or NSC23766 may therefore represent a potential treatment against aortic aneurysm and dissection.

Cell fate regulation governed by p53: Friends or reversible foes in cancer therapy

Cancer is a leading cause of death worldwide. Targeted therapies aimed at key oncogenic driver mutations in combination with chemotherapy and radiotherapy as well as immunotherapy have benefited cancer patients considerably. Tumor protein p53 (TP53), a crucial tumor suppressor gene encoding p53, regulates numerous downstream genes and cellular phenotypes in response to various stressors. The affected genes are involved in diverse processes, including cell cycle arrest, DNA repair, cellular senescence, metabolic homeostasis, apoptosis, and autophagy. However, accumulating recent studies have continued to reveal novel and unexpected functions of p53 in governing the fate of tumors, for example, functions in ferroptosis, immunity, the tumor microenvironment and microbiome metabolism. Among the possibilities, the evolutionary plasticity of p53 is the most controversial, partially due to the dizzying array of biological functions that have been attributed to different regulatory mechanisms of p53 signaling. Nearly 40 years after its discovery, this key tumor suppressor remains somewhat enigmatic. The intricate and diverse functions of p53 in regulating cell fate during cancer treatment are only the tip of the iceberg with respect to its equally complicated structural biology, which has been painstakingly revealed. Additionally, TP53 mutation is one of the most significant genetic alterations in cancer, contributing to rapid cancer cell growth and tumor progression. Here, we summarized recent advances that implicate altered p53 in modulating the response to various cancer therapies, including chemotherapy, radiotherapy, and immunotherapy. Furthermore, we also discussed potential strategies for targeting p53 as a therapeutic option for cancer.

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.

Metabolic enzyme LDHA activates Rac1 GTPase as a noncanonical mechanism to promote cancer

The glycolytic enzyme lactate dehydrogenase A (LDHA) is frequently overexpressed in cancer, which promotes glycolysis and cancer. The oncogenic effect of LDHA has been attributed to its glycolytic enzyme activity. Here we report an unexpected noncanonical oncogenic mechanism of LDHA; LDHA activates small GTPase Rac1 to promote cancer independently of its glycolytic enzyme activity. Mechanistically, LDHA interacts with the active form of Rac1, Rac1-GTP, to inhibit Rac1-GTP interaction with its negative regulator, GTPase-activating proteins, leading to Rac1 activation in cancer cells and mouse tissues. In clinical breast cancer specimens, LDHA overexpression is associated with higher Rac1 activity. Rac1 inhibition suppresses the oncogenic effect of LDHA. Combination inhibition of LDHA enzyme activity and Rac1 activity by small-molecule inhibitors displays a synergistic inhibitory effect on breast cancers with LDHA overexpression. These results reveal a critical oncogenic mechanism of LDHA and suggest a promising therapeutic strategy for breast cancers with LDHA overexpression.

Leukemia inhibitory factor drives glucose metabolic reprogramming to promote breast tumorigenesis

LIF, a multifunctional cytokine, is frequently overexpressed in many types of solid tumors, including breast cancer, and plays an important role in promoting tumorigenesis. Currently, how LIF promotes tumorigenesis is not well-understood. Metabolic reprogramming is a hallmark of cancer cells and a key contributor to cancer progression. However, the role of LIF in cancer metabolic reprogramming is unclear. In this study, we found that LIF increases glucose uptake and drives glycolysis, contributing to breast tumorigenesis. Blocking glucose uptake largely abolishes the promoting effect of LIF on breast tumorigenesis. Mechanistically, LIF overexpression enhances glucose uptake via activating the AKT/GLUT1 axis to promote glycolysis. Blocking the AKT signaling by shRNA or its inhibitors greatly inhibits glycolysis driven by LIF and largely abolishes the promoting effect of LIF on breast tumorigenesis. These results demonstrate an important role of LIF overexpression in glucose metabolism reprogramming in breast cancers, which contributes to breast tumorigenesis. This study also reveals an important mechanism underlying metabolic reprogramming of breast cancers, and identifies LIF and its downstream signaling as potential therapeutic targets for breast cancers, especially those with LIF overexpression.

Hepatic Ischemia-reperfusion Injury in Mice was Alleviated by Rac1 Inhibition - More Than Just ROS-inhibition

BACKGROUND AND AIMS

Reducing reactive oxygen species (ROS) production has proven an effective way for alleviating oxidative stress during ischemia-reperfusion injury (IRI). Moreover, inhibition of Rac1 could reduce ROS production and prevent oxidative stress injury. Previous studies have suggested a positive interactivation feedback loop between Rac1 and hypoxia-inducible factor (HIF)-1α, the latter being up-regulated early during ischemia. The positive inter-activation between Rac1 and HIF-1α would aggravate ROS production, thereby promoting IRI. This study was designed to verify the effects of Rac1 inhibition on hepatic IRI both at animal and cellular levels and to explore the interaction between Rac1 and HIF-1α during hepatic IRI.

METHODS

C57B/6 mice and AML-12 cells were used for the construction of hepatic IRI animal and cell models. Rac1 inhibition was achieved by NSC23766 (a specific Rac1 inhibitor). Lentiviral vectors were used for Rac1 knockdown. At designated time points, serum and liver tissues were collected from the mice and treated cells were collected for further analysis.

RESULTS

NSC23766 treatment significantly alleviated the hepatic IRI in mice, manifesting as lower vacuolation score and less apoptosis cells, lower ROS and serum/liver alanine aminotransferase/aspartate aminotransferase levels, and fewer activated inflammatory cells. IRI of AML-12 was also alleviated by 50 µM NSC23766 or Rac1-knockdown, manifesting as reduced cell apoptosis, less extensive interruption of mitochondrial membrane potential, down-regulation of apoptosis, and effects on DNA damage-related proteins. Interestingly, Rac1 knockdown also down-regulated the expression level of HIF-1α.

CONCLUSIONS

Our study supports a protective effect of Rac1 inhibition on hepatic IRI. Aside from the classic topics of reducing ROS production and oxidative stress, our study showed an interaction between Rac1 and HIF-1α signaling during hepatic IRI.

Regulation of p53 Function by Formation of Non-Nuclear Heterologous Protein Complexes

A transcription factor p53 is activated upon cellular exposure to endogenous and exogenous stresses, triggering either homeostatic correction or cell death. Depending on the stress level, often measurable as DNA damage, the dual outcome is supported by p53 binding to a number of regulatory and metabolic proteins. Apart from the nucleus, p53 localizes to mitochondria, endoplasmic reticulum and cytosol. We consider non-nuclear heterologous protein complexes of p53, their structural determinants, regulatory post-translational modifications and the role in intricate p53 functions. The p53 heterologous complexes regulate the folding, trafficking and/or action of interacting partners in cellular compartments. Some of them mainly sequester p53 (HSP proteins, G6PD, LONP1) or its partners (RRM2B, PRKN) in specific locations. Formation of other complexes (with ATP2A2, ATP5PO, BAX, BCL2L1, CHCHD4, PPIF, POLG, SOD2, SSBP1, TFAM) depends on p53 upregulation according to the stress level. The p53 complexes with SIRT2, MUL1, USP7, TXN, PIN1 and PPIF control regulation of p53 function through post-translational modifications, such as lysine acetylation or ubiquitination, cysteine/cystine redox transformation and peptidyl-prolyl cis-trans isomerization. Redox sensitivity of p53 functions is supported by (i) thioredoxin-dependent reduction of p53 disulfides, (ii) inhibition of the thioredoxin-dependent deoxyribonucleotide synthesis by p53 binding to RRM2B and (iii) changed intracellular distribution of p53 through its oxidation by CHCHD4 in the mitochondrial intermembrane space. Increasing knowledge on the structure, function and (patho)physiological significance of the p53 heterologous complexes will enable a fine tuning of the settings-dependent p53 programs, using small molecule regulators of specific protein–protein interactions of p53.

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.

FOXO3a inhibits nephroblastoma cell proliferation, migration and invasion, and induces apoptosis through downregulating the Wnt/β‑catenin signaling pathway

Forkhead transcription factor O subfamily 3A (FOXO3a) is an important tumor suppressor gene that is expressed in renal tissue and has been reported to be downregulated in clear cell renal cell carcinoma (CCRCC). Notably, the overexpression of FOXO3a was previously discovered to inhibit the progression of CCRCC. However, the expression levels of FOXO3a in nephroblastoma cell lines remain unknown. The present study aimed to investigate the expression levels of FOXO3a in nephroblastoma cell lines and to determine the mechanism of action of the biological functions of FOXO3a. Western blotting and reverse transcription‑quantitative PCR were used to analyze the expression levels of FOXO3a in nephroblastoma cell lines. Subsequently, the effects of the overexpression of FOXO3a and the genetic knockdown of the Wnt/β‑catenin signaling protein Axin‑2 on the biological functions were determined through Cell Counting Kit‑8, cell colony formation assays, scratch and Transwell assay and flow cytometric analysis experiments. The expression levels of FOXO3a were discovered to be downregulated in nephroblastoma cell lines. The overexpression of FOXO3a inhibited the proliferation, invasion and migration of nephroblastoma cells, while inducing apoptosis. Furthermore, the overexpression of FOXO3a downregulated the expression levels of β‑catenin and Cyclin‑D1 proteins involved in the Wnt/β‑catenin signaling pathway. Cell proliferation and the migration and invasion ability of 17‑94 cells in shRNA‑Axin2‑2 group were promoted. Cell apoptosis was predominantly increased by overexpressed FOXO3a, which was reversed by shRNA‑Axin2‑1. The biological effects of overexpressing FOXO3a on nephroblastoma were reversed after activation of Wnt/β‑catenin. In conclusion, the findings of the present study suggested that FOXO3a may inhibit nephroblastoma cell proliferation, migration and invasion, while inducing apoptosis, by downregulating the Wnt/β‑catenin signaling pathway. These results may provide a novel method for the early diagnosis and precise treatment of nephroblastoma.

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.

The Function of the Mutant p53-R175H in Cancer

Wild-type p53 is known as "the guardian of the genome" because of its function of inducing DNA repair, cell-cycle arrest, and apoptosis, preventing the accumulation of gene mutations. TP53 is highly mutated in cancer cells and most TP53 hotspot mutations are missense mutations. Mutant p53 proteins, encoded by these hotspot mutations, lose canonical wild-type p53 functions and gain functions that promote cancer development, including promoting cancer cell proliferation, migration, invasion, initiation, metabolic reprogramming, angiogenesis, and conferring drug resistance to cancer cells. Among these hotspot mutations, p53-R175H has the highest occurrence. Although losing the transactivating function of the wild-type p53 and prone to aggregation, p53-R175H gains oncogenic functions by interacting with many proteins. In this review, we summarize the gain of functions of p53-R175H in different cancer types, the interacting proteins of p53-R175H, and the downstream signaling pathways affected by p53-R175H to depict a comprehensive role of p53-R175H in cancer development. We also summarize treatments that target p53-R175H, including reactivating p53-R175H with small molecules that can bind to p53-R175H and alter it into a wild-type-like structure, promoting the degradation of p53-R175H by targeting heat-shock proteins that maintain the stability of p53-R175H, and developing immunotherapies that target the p53-R175H-HLA complex presented by tumor cells.

Wrestling and Wrapping: A Perspective on SUMO Proteins in Schwann Cells

Schwann cell development and peripheral nerve myelination are finely orchestrated multistep processes; some of the underlying mechanisms are well described and others remain unknown. Many posttranslational modifications (PTMs) like phosphorylation and ubiquitination have been reported to play a role during the normal development of the peripheral nervous system (PNS) and in demyelinating neuropathies. However, a relatively novel PTM, SUMOylation, has not been studied in these contexts. SUMOylation involves the covalent attachment of one or more small ubiquitin-like modifier (SUMO) proteins to a substrate, which affects the function, cellular localization, and further PTMs of the conjugated protein. SUMOylation also regulates other proteins indirectly by facilitating non-covalent protein–protein interaction via SUMO interaction motifs (SIM). This pathway has important consequences on diverse cellular processes, and dysregulation of this pathway has been reported in several diseases including neurological and degenerative conditions. In this article, we revise the scarce literature on SUMOylation in Schwann cells and the PNS, we propose putative substrate proteins, and we speculate on potential mechanisms underlying the possible involvement of this PTM in peripheral myelination and neuropathies.

DNAJA1 promotes cancer metastasis through interaction with mutant p53

Accumulation of mutant p53 (mutp53) is crucial for its oncogenic gain of function activity. DNAJA1, a member of J-domain containing proteins or heat shock protein 40, is shown to prevent unfolded mutp53 from proteasomal degradation. However, the biological function of DNAJA1 remains largely unknown. Here we show that DNAJA1 promotes tumor metastasis by accumulating unfolded mutp53. Levels of DNAJA1 in head and neck squamous cell carcinoma (HNSCC) tissues were higher than those in normal tissues. Knockdown of DNAJA1 in HNSCC cell lines carrying unfolded mutp53 significantly decreased the levels of mutp53, filopodia/lamellipodia formation, migratory potential, and active forms of CDC42/RAC1, which were not observed in HNSCC cells with DNA contact mutp53, wild-type p53, or p53 null. Such mutp53-dependent functions of DNAJA1 were supported by the observation that DNAJA1 selectively bound to unfolded mutp53. Moreover, DNAJA1 knockdown in HNSCC cells carrying unfolded mutp53 inhibited primary tumor growth and metastases to the lymph nodes and lungs. Our study suggests that DNAJA1 promotes HNSCC metastasis mainly in a manner dependent on mutp53 status, suggesting DNAJA1 as a potential therapeutic target for HNSCC harboring unfolded mutp53.

Tumor suppressor p53 regulates intestinal type 2 immunity

The role of p53 in tumor suppression has been extensively studied and well-established. However, the role of p53 in parasitic infections and the intestinal type 2 immunity is unclear. Here, we report that p53 is crucial for intestinal type 2 immunity in response to the infection of parasites, such as Tritrichomonas muris and Nippostrongylus brasiliensis. Mechanistically, p53 plays a critical role in the activation of the tuft cell-IL-25-type 2 innate lymphoid cell circuit, partly via transcriptional regulation of Lrmp in tuft cells. Lrmp modulates Ca2+ influx and IL-25 release, which are critical triggers of type 2 innate lymphoid cell response. Our results thus reveal a previously unrecognized function of p53 in regulating intestinal type 2 immunity to protect against parasitic infections, highlighting the role of p53 as a guardian of immune integrity.

Plasma Exosome-Derived Sentrin SUMO-Specific Protease 1: A Prognostic Biomarker in Patients With Osteosarcoma

Background

The exosomes contain many important proteins that can be used for early tumor diagnosis or patient prognosis analysis. In this study, we investigated plasma exosome-derived sentrin SUMO-specific protease 1 (SENP1) levels as a prognostic biomarker in patients with osteosarcoma.

Methods

The expression of SENP1 protein in osteosarcoma tissues and adjacent tissues was detected by immunohistochemistry (IHC). The exosomes were identified by transmission electron microscopy, nanoparticle tracking analysis, and western blotting. ELISA was used to detect plasma exosome-derived SENP1 levels to assess prognosis in patients with osteosarcoma.

Results

IHC showed that the positive expression rate of SENP1 in osteosarcoma tissues was 88.33%, whereas that in adjacent tissues was 46.67% (P < 0.05). Plasma exosome-derived SENP1 levels were related to tumor size, tumor location, necrosis rate, pulmonary metastasis, and surgical stage. Both disease-free survival (DFS) and overall survival (OS) were worse in patients who had higher plasma exosome-derived SENP1 levels compared with those in patients with lower plasma exosome-derived SENP1 levels (P < 0.001). The area under the receiver operating characteristic curve (AUROC) of plasma exosome-derived SENP1, as 1-year DFS and 3-year DFS prognostic biomarkers, was 0.90 (95% CI: 0.83-0.98) and 0.96 (95% CI: 0.94-0.99), respectively. As to OS, the AUROC of plasma exosome-derived SENP1 for 1-year and 3-year prediction was 0.90 (95% CI: 0.82-0.99) and 0.96 (0.93-0.98), respectively. The plasma exosome-derived SENP1 was better than plasma SENP1 as a prognostic biomarker both in DFS and OS.

Conclusions

Our findings show that the plasma exosome-derived SENP1 may serve as a novel and independent prognostic predictor in clinical applications.

GTPases, genome, actin: A hidden story in DNA damage response and repair mechanisms

The classical small Rho GTPase (Rho, Rac, and Cdc42) protein family is mainly responsible for regulating cell motility and polarity, membrane trafficking, cell cycle control, and gene transcription. Cumulative recent evidence supports important roles for these proteins in the maintenance of genomic stability. Indeed, DNA damage response (DDR) and repair mechanisms are some of the prime biological processes that underlie several disease phenotypes, including genetic disorders, cancer, senescence, and premature aging. Many reports guided by different experimental approaches and molecular hypotheses have demonstrated that, to some extent, direct modulation of Rho GTPase activity, their downstream effectors, or actin cytoskeleton regulation contribute to these cellular events. Although much attention has been paid to this family in the context of canonical actin cytoskeleton remodeling, here we provide a contextualized review of the interplay between Rho GTPase signaling pathways and the DDR and DNA repair signaling components. Interesting questions yet to be addressed relate to the spatiotemporal dynamics of this collective response and whether it correlates with different subcellular pools of Rho GTPases. We highlight the direct and indirect targets, some of which still lack experimental validation data, likely associated with Rho GTPase activation that provides compelling evidence for further investigation in DNA damage-associated events and with potential therapeutic applications in translational medicine.

LINC00460-miR-149-5p/miR-150-5p-Mutant p53 Feedback Loop Promotes Oxaliplatin Resistance in Colorectal Cancer

Oxaliplatin resistance is a major challenge in the clinical treatment for advanced colorectal cancer (CRC). Long non-coding RNAs (lncRNAs) are involved in tumorigenesis and progression as critical regulators, while their potential roles in chemoresistance are poorly understood. In this study, we report that the LINC00460-miR-149-5p/miR-150-5p-mutant p53 feedback loop is responsible for oxaliplatin resistance in CRC. First, LINC00460 was found to exhibit higher expression in oxaliplatin-resistant CRC (CRC/OxR) cells compared with parental oxaliplatin-sensitive ones, and this expression pattern depends on mutant p53 (SW480/OxR), not wild-type p53 (HCT116/OxR). Oxaliplatin-induced LINC00460 in SW480/OxR cells was mainly located in the cytoplasm and was associated with AGO2 protein. LINC00460 functions as a competing endogenous RNA (ceRNA) to promote oxaliplatin resistance through sequestering miR-149-5p/miR-150-5p and upregulating the expression of the microRNA (miRNA) target p53. Knockdown of LINC00460 sensitized SW480/OxR cells to oxaliplatin by modulating p53 in vitro and in vivo. In turn, mutant p53 positively regulated the expression of LINC00460, thus forming a feedback loop. Clinical data showed that LINC00460 was upregulated in CRC tissues compared with paired normal tissues and was significantly correlated with clinical stage and node (N) status. Our findings uncover a mechanism for the LINC00460-miR-149-5p/miR-150-5p-mutant p53 feedback loop in oxaliplatin resistance of CRC, and they provide potential therapeutic targets for tumor chemoresistance.

Participation of MicroRNAs in the Treatment of Cancer with Phytochemicals

Cancer is a global health concern and one of the main causes of disease-related death. Even with considerable progress in investigations on cancer therapy, effective anti-cancer agents and regimens have thus far been insufficient. There has been compelling evidence that natural phytochemicals and their derivatives have potent anti-cancer activities. Plant-based anti-cancer agents, such as etoposide, irinotecan, paclitaxel, and vincristine, are currently being applied in medical treatments for patients with cancer. Further, the efficacy of plenty of phytochemicals has been evaluated to discover a promising candidate for cancer therapy. For developing more effective cancer therapy, it is required to apprehend the molecular mechanism deployed by natural compounds. MicroRNAs (miRNAs) have been realized to play a pivotal role in regulating cellular signaling pathways, affecting the efficacy of therapeutic agents in cancer. This review presents a feature of phytochemicals with anti-cancer activity, focusing mainly on the relationship between phytochemicals and miRNAs, with insights into the role of miRNAs as the mediators and the regulators of anti-cancer effects of phytochemicals.

Active RAC1 Promotes Tumorigenic Phenotypes and Therapy Resistance in Solid Tumors

Acting as molecular switches, all three members of the Guanosine triphosphate (GTP)-ase-family, Ras-related C3 botulinum toxin substrate (RAC), Rho, and Cdc42 contribute to various processes of oncogenic transformations in several solid tumors. We have reviewed the distribution of patterns regarding the frequency of Ras-related C3 botulinum toxin substrate 1 (RAC1)-alteration(s) and their modes of actions in various cancers. The RAC1 hyperactivation/copy-number gain is one of the frequently observed features in various solid tumors. We argued that RAC1 plays a critical role in the progression of tumors and the development of resistance to various therapeutic modalities applied in the clinic. With this perspective, here we interrogated multiple functions of RAC1 in solid tumors pertaining to the progression of tumors and the development of resistance with a special emphasis on different tumor cell phenotypes, including the inhibition of apoptosis and increase in the proliferation, epithelial-to-mesenchymal transition (EMT), stemness, pro-angiogenic, and metastatic phenotypes. Our review focuses on the role of RAC1 in adult solid-tumors and summarizes the contextual mechanisms of RAC1 involvement in the development of resistance to cancer therapies.

Dysregulation of Rho GTPases in Human Cancers

Rho GTPases play central roles in numerous cellular processes, including cell motility, cell polarity, and cell cycle progression, by regulating actin cytoskeletal dynamics and cell adhesion. Dysregulation of Rho GTPase signaling is observed in a broad range of human cancers, and is associated with cancer development and malignant phenotypes, including metastasis and chemoresistance. Rho GTPase activity is precisely controlled by guanine nucleotide exchange factors, GTPase-activating proteins, and guanine nucleotide dissociation inhibitors. Recent evidence demonstrates that it is also regulated by post-translational modifications, such as phosphorylation, ubiquitination, and sumoylation. Here, we review the current knowledge on the role of Rho GTPases, and the precise mechanisms controlling their activity in the regulation of cancer progression. In addition, we discuss targeting strategies for the development of new drugs to improve cancer therapy.

Gain of function mutant p53 protein activates AKT through the Rac1 signaling to promote tumorigenesis

Tumor suppressor p53 is the most frequently mutated gene in human cancer. Mutant p53 (mutp53) not only loses the tumor suppressive activity of wild type p53, but often gains new oncogenic activities to promote tumorigenesis, defined as mutp53 gain of function (GOF). While the concept of mutp53 GOF is well-established, its underlying mechanism is not well-understood. AKT has been suggested to be activated by mutp53 and contribute to mutp53 GOF, but its underlying mechanism is unclear. In this study, we found that the activation of the Rac1 signaling by mutp53 mediates the promoting effect of mutp53 on AKT activation. Blocking Rac1 signaling by RNAi or a Rac1 inhibitor can inhibit AKT activation by mutp53. Importantly, targeting Rac1/AKT can greatly compromise mutp53 GOF in tumorigenesis. Results from this study uncover a new mechanism for AKT activation in tumors, and reveal that activation of AKT by mutp53 via the Rac1 signaling contributes to mutp53 GOF in tumorigenesis. More importantly, this study provides Rac1 and AKT as potential targets for therapy in tumors containing mutp53.

Rac1 Signaling: From Intestinal Homeostasis to Colorectal Cancer Metastasis

The small GTPase Rac1 has been implicated in a variety of dynamic cell biological processes, including cell proliferation, cell survival, cell-cell contacts, epithelial mesenchymal transition (EMT), cell motility, and invasiveness. These processes are orchestrated through the fine tuning of Rac1 activity by upstream cell surface receptors and effectors that regulate the cycling Rac1-GDP (off state)/Rac1-GTP (on state), but also through the tuning of Rac1 accumulation, activity, and subcellular localization by post translational modifications or recruitment into molecular scaffolds. Another level of regulation involves Rac1 transcripts stability and splicing. Downstream, Rac1 initiates a series of signaling networks, including regulatory complex of actin cytoskeleton remodeling, activation of protein kinases (PAKs, MAPKs) and transcription factors (NFkB, Wnt/β-catenin/TCF, STAT3, Snail), production of reactive oxygen species (NADPH oxidase holoenzymes, mitochondrial ROS). Thus, this GTPase, its regulators, and effector systems might be involved at different steps of the neoplastic progression from dysplasia to the metastatic cascade. After briefly placing Rac1 and its effector systems in the more general context of intestinal homeostasis and in wound healing after intestinal injury, the present review mainly focuses on the several levels of Rac1 signaling pathway dysregulation in colorectal carcinogenesis, their biological significance, and their clinical impact.

Tumor-Suppressive MicroRNA-216b Binds to TPX2, Activating the p53 Signaling in Human Cutaneous Squamous Cell Carcinoma

Dysregulation of microRNAs (miRNAs) is acknowledged in human cutaneous squamous cell carcinoma (cSCC). We hereby evaluated the ability of miRNA-216b (miR-216b) to impact human cSCC. cSCC tissues with corresponding adjacent normal tissues were collected from 40 patients diagnosed with cSCC where the expression pattern of miR-216b and targeting protein for Xenopus kinesin-like protein 2 (TPX2) was determined by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and western blot analysis. A431 cells were transfected with miR-216b mimic, miR-216b inhibitor, or short interfering RNA against TPX2 to evaluate cell proliferation, invasion, migration, and apoptosis using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, scratch test, Transwell assay, and flow cytometry. TPX2 was highly expressed in cSCC tissues while miR-216b was poorly expressed in association with tumor differentiation, lymph node metastasis, and tumor node metastasis staging in patients with cSCC. In response to overexpressed miR-216b or silenced TPX2, cSCC cell proliferation, invasion, and migration were suppressed and apoptosis was stimulated, along with activated p53 signaling. Thus, upregulated miR-216b was capable of promoting apoptosis and inhibiting proliferation, invasion, and migration of cSCC cells by downregulating TPX2 through activation of the p53 signaling, highlighting a novel biomarker for novel treatment modalities against cSCC.

Mutant p53 Gain-of-Function: Role in Cancer Development, Progression, and Therapeutic Approaches

Frequent p53 mutations (mutp53) not only abolish tumor suppressor capacities but confer various gain-of-function (GOF) activities that impacts molecules and pathways now regarded as central for tumor development and progression. Although the complete impact of GOF is still far from being fully understood, the effects on proliferation, migration, metabolic reprogramming, and immune evasion, among others, certainly constitute major driving forces for human tumors harboring them. In this review we discuss major molecular mechanisms driven by mutp53 GOF. We present novel mechanistic insights on their effects over key functional molecules and processes involved in cancer. We analyze new mechanistic insights impacting processes such as immune system evasion, metabolic reprogramming, and stemness. In particular, the increased lipogenic activity through the mevalonate pathway (MVA) and the alteration of metabolic homeostasis due to interactions between mutp53 and AMP-activated protein kinase (AMPK) and Sterol regulatory element-binding protein 1 (SREBP1) that impact anabolic pathways and favor metabolic reprograming. We address, in detail, the impact of mutp53 over metabolic reprogramming and the Warburg effect observed in cancer cells as a consequence, not only of loss-of-function of p53, but rather as an effect of GOF that is crucial for the imbalance between glycolysis and oxidative phosphorylation. Additionally, transcriptional activation of new targets, resulting from interaction of mutp53 with NF-kB, HIF-1α, or SREBP1, are presented and discussed. Finally, we discuss perspectives for targeting molecules and pathways involved in chemo-resistance of tumor cells resulting from mutp53 GOF. We discuss and stress the fact that the status of p53 currently constitutes one of the most relevant criteria to understand the role of autophagy as a survival mechanism in cancer, and propose new therapeutic approaches that could promote the reduction of GOF effects exercised by mutp53 in cancer.

Loss of ubiquitin-conjugating enzyme E2 (Ubc9) in macrophages exacerbates multiple low-dose streptozotocin-induced diabetes by attenuating M2 macrophage polarization

Type 1 diabetes (T1D) is characterized by the selective autoimmune destruction of the islet β cells, and macrophages play a significant role in this process. Small ubiquitin-like modification (SUMOylation) is an important posttranslational modification involved in T1D pathogenesis, but its function in macrophages remains unexplored. We presently developed and used macrophage-specific ubiquitin-conjugating enzyme E2 (Ubc9) knockout (LyzM-Cre-Ubc9^fl/fl, KO) mice to address the impact of SUMOylation on macrophage function in a T1D model. We observed that blocking Ubc9 in macrophages exacerbated multiple-low dose streptozotocin (MLD-STZ)-induced diabetes. Specifically, after STZ treatment, blood glucose levels were consistently elevated in the KO mice. The KO mice exhibited a higher diabetes incidence than WT controls (85% vs. 55%, P < 0.01) along with a higher insulitis severity. The loss of Ubc9 impaired macrophage energy metabolism and attenuated macrophage M2 program, thereby enhancing T cell activation. Pancreas-resident macrophages, rather than migrant macrophages, played a predominant role in MLD-STZ-induced diabetes. Mechanistically, Ubc9-mediated SUMOylation of interferon regulator factor 4 (IRF4) enhanced its nuclear localization and stability, thereby transcribing IL-4 and arginase 1 (Arg1) to promote the macrophage M2 program. Ubc9-mediated SUMOylation modulates T1D risk at least in part by regulating macrophage function. Modulation of disturbed SUMOylation process in macrophages, either through cell adoptive transfer or targeted drug-delivery, could help to establish a tolerant pancreatic microenvironment and promote inflammation resolution in early insulitis stage, thus hindering T1D progression.

Mutant p53 drives cancer chemotherapy resistance due to loss of function on activating transcription of PUMA

P53 is a critical tumor suppressor gene, activating p53 and its downstream targets to induce apoptosis is a promising way for cancer therapy. However, more than 50% of cancer patients have p53 mutations, which may cause cancer therapy resistance, and the underline mechanism is poorly understood. Here, we found that cell viability decrease and apoptosis induced by p53-dependent traditional drugs in colon cancer cells were eliminated in p53 mutant cells. Mutant p53 did not up-regulate the expression of its direct downstream targets PUMA and p21, due to the inhibition of PUMA transcription. Furthermore, mutant p53 could not bind to the promoter of PUMA to activate its transcription like WT p53 did, while overexpressed WT p53 rescued PUMA-induced subsequent apoptosis. In conclusion, our findings demonstrate mutant p53 may cause chemo-resistance of tumor because of inactivating PUMA transcription, which prompts some new insights for clinical therapy of cancer patients with mutant p53.Abbreviations: CRC: Colorectal cancer; CDKs: Cyclin-dependent kinases; PUMA: p53 up-regulated modulator of apoptosis; PDGF: the platelet-derived growth factor; WT p53: wild-type p53 protein; mutp53: mutant p53 proteins; BAX: Bcl-2-associated X protein; NOXA: Phorbol-12-myristate-13-acetate-induced protein 1.

Conditional Deletion of CC2D1A Reduces Hippocampal Synaptic Plasticity and Impairs Cognitive Function through Rac1 Hyperactivation

Coiled-coil and C2 domain containing 1A (CC2D1A) is an evolutionarily conserved protein, originally identified as a nuclear factor-κB activator through a large-scale screen of human genes. Mutations in the human Cc2d1a gene result in autosomal recessive nonsyndromic intellectual disability. It remains unclear, however, how Cc2d1a mutation leads to alterations in brain function. Here, we have taken advantage of Cre/loxP recombinase-based strategy to conditionally delete Cc2d1a exclusively from excitatory neurons of male mouse forebrain to examine its role in hippocampal synaptic plasticity and cognitive function. We confirmed the expression of CC2D1A protein and mRNA in the mouse hippocampus. Double immunofluorescence staining showed that CC2D1A is expressed in both excitatory and inhibitory neurons of the adult hippocampus. Conditional deletion of Cc2d1a (cKO) from excitatory neurons leads to impaired performance in object location memory test and altered anxiety-like behavior. Consistently, cKO mice displayed a deficit in the maintenance of LTP in the CA1 region of hippocampal slices. Cc2d1a deletion also resulted in decreased complexity of apical and basal dendritic arbors of CA1 pyramidal neurons. An enhanced basal Rac1 activity was observed following Cc2d1a deletion, and this enhancement was mediated by reduced SUMO-specific protease 1 (SENP1) and SENP3 expression, thus increasing the amount of Rac1 SUMOylation. Furthermore, partial blockade of Rac1 activity rescued impairments in LTP and object location memory performance in cKO mice. Together, our results implicate Rac1 hyperactivity in synaptic plasticity and cognitive deficits observed in Cc2d1a cKO mice and reveal a novel role for CC2D1A in regulating hippocampal synaptic function.SIGNIFICANCE STATEMENT CC2D1A is abundantly expressed in the brain, but there is little known about its physiological function. Taking advantage of Cc2d1a cKO mice, the present study highlights the importance of CC2D1A in the maintenance of LTP at Schaffer collateral-CA1 synapses and the formation of hippocampus-dependent long-term object location memory. Our findings establish a critical link between elevated Rac1 activity, structural and synaptic plasticity alterations, and cognitive impairment caused by Cc2d1a deletion. Moreover, partial blockade of Rac1 activity rescues synaptic plasticity and memory deficits in Cc2d1a cKO mice. Such insights may have implications for the utility of Rac1 inhibitors in the treatment of intellectual disability caused by Cc2d1a mutations in human patients.

Functional Diversity of p53 in Human and Wild Animals

The common understanding of p53 function is a genome guardian, which is activated by diverse stresses stimuli and mediates DNA repair, apoptosis, and cell cycle arrest. Increasing evidence has demonstrated p53 new cellular functions involved in abundant endocrine and metabolic response for maintaining homeostasis. However, TP53 is frequently mutant in human cancers, and the mutant p53 (Mut-p53) turns to an "evil" cancer-assistant. Mut-p53-induced epithelial-mesenchymal transition (EMT) plays a crucial role in the invasion and metastasis of endocrine carcinomas, and Mut-p53 is involved in cancer immune evasion by upregulating PD-L1 expression. Therefore, Mut-p53 is a valuable treatment target for malignant tumors. Targeting Mut-p53 in correcting sequence and conformation are increasingly concerned. Interestingly, in wild animals, p53 variations contribute to cancer resistant and high longevity. This review has discussed the multiple functions of p53 in health, diseases, and nature evolution, summarized the frequently mutant sites of p53, and the mechanisms of Mut-p53-mediated metastasis and immune evasion in endocrine cancers. We have provided a new insight for multiple roles of p53 in human and wild animals.

Role of small ubiquitin-like modifier proteins-1 (SUMO-1) in regulating migration and invasion of fibroblast-like synoviocytes from patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is featured by erosive cartilage and bone destruction. The enhancing aggressive property of fibroblast-like synoviocytes (FLSs) plays a critical role in this process. Small ubiquitin-like modifier (SUMO) proteins, including SUMO-1, SUMO-2, SUMO-3 and SUMO-4, participate in regulating many cellular events such as survival, migration and signal transduction in some cell lines. However, their roles in the pathogenesis of RA are not well established. Therefore, we evaluated the role of SUMO proteins in RA FLSs migration and invasion. We found that expression of both SUMO-1 and SUMO-2 was elevated in FLSs and synovial tissues (STs) from patients with RA. SUMO-1 suppression by small interference RNA (siRNA) reduced migration and invasion as well as MMP-1 and MMP-3 expression in RA FLSs. We also demonstrated that SUMO-1 regulated lamellipodium formation during cell migration. To explore further into molecular mechanisms, we evaluated the effect of SUMO-1 knockdown on the activation of Rac1/PAK1, a critical signaling pathway that controls cell motility. Our results indicated that SUMO-1-mediated SUMOylation controlled Rac1 activation and modulated downstream PAK1 activity. Inhibition of Rac1 or PAK1 also decreased migration and invasion of RA FLSs. Our findings suggest that SUMO-1 suppression could be protective against joint destruction in RA by inhibiting aggressive behavior of RA FLSs.

Interferon-stimulated gene 15 enters posttranslational modifications of p53

The tumor suppressor protein p53 is a central governor of various cellular signals. It is well accepted that ubiquitination as well as ubiquitin-like (UBL) modifications of p53 protein is critical in the control of its activity. Interferon-stimulated gene 15 (ISG15) is a well-known UBL protein with pleiotropic functions, serving both as a free intracellular molecule and as a modifier by conjugating to target proteins. Initially, attentions have historically focused on the antiviral effects of ISG15 pathway. Remarkably, a significant role in the processes of autophagy, DNA repair, and protein translation provided considerable insight into the new functions of ISG15 pathway. Despite the deterministic revelation of the relation between ISG15 and p53, the functional consequence of p53 ISGylation appears somewhat confused. More important, more recent studies have hinted p53 ubiquitination or other UBL modifications that might interconnect with its ISGylation. Here, we aim to summarize the current knowledge of p53 ISGylation and the differences in other significant modifications, which would be beneficial for the development of p53-based cancer therapy.

Control of SUMO and Ubiquitin by ROS: Signaling and disease implications

Reversible post-translational modifications (PTMs) ensure rapid signal transmission from sensors to effectors. Reversible modification of proteins by the small proteins Ubiquitin and SUMO are involved in virtually all cellular processes and can modify thousands of proteins. Ubiquitination or SUMOylation is the reversible attachment of these modifiers to lysine residues of a target via isopeptide bond formation. These modifications require ATP and an enzymatic cascade composed of three classes of proteins: E1 activating enzymes, E2 conjugating enzymes and E3 ligases. The reversibility of the modification is ensured by specific isopeptidases. E1 and E2 enzymes, some E3 ligases and most isopeptidases have catalytic cysteine residues, which make them potentially susceptible for oxidation. Indeed, an increasing number of examples reveal regulation of ubiquitination and SUMOylation by reactive oxygen species, both in the context of redox signaling and in severe oxidative stress. Importantly, ubiquitination and SUMOylation play essential roles in the regulation of ROS homeostasis, participating in the control of ROS production and clearance. In this review, we will discuss the interplay between ROS homeostasis, Ubiquitin and SUMO pathways and the implications for the oxidative stress response and cell signaling.

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.

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.