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.

Gain-of-function mutations of AtNHX1 suppress sos1 salt sensitivity and improve salt tolerance in Arabidopsis

Soil salinity severely hampers agricultural productivity.Under salt stress,excess Na+accumulation causes cellular damage and plant growth retardation,and membrane Na+transporters play central roles in Na+uptake and exclusion to mitigate these adverse effects.In this study,we performed sos1 suppressor mutant(named sup)screening to uncover potential genetic interactors of SOS1 and additional salt tolerance mechanisms.Map-based cloning and sequencing identified a group of mutants harboring dominant gain-of-function mutations in the vacuolar Na+/H+antiporter gene AtNHX1.The gain-of-function variants of AtNHX1 showed enhanced transporter activities in yeast cells and increased salt tolerance in Arabidopsis wild type plants.Ion content measurements indicated that at the cellular level,these gain-of-function mutations resulted in increased cellular Na+accumulation likely due to enhanced vacuolar Na+sequestration.However,the gain-of-function suppressor mutants showed reduced shoot Na+but increased root Na+accumulation under salt stress,indicating a role of AtNHX1 in limiting Na+translocation from root to shoot.We also identified another group of sos1 suppressors with loss-of-function mutations in the Na+transporter gene AtHKT1.Loss-of-function mutations in AtHKT1 and gain-of-function mutations in AtNHX1 additively suppressed sos1 salt sensitivity,which indicates that the three transporters,SOS1,AtNHX1 and AtHKT1 function independently but coordinately in controlling Na+homeostasis and salt tolerance in Arabidopsis.Our findings provide valuable information about the target amino acids in NHX1 for gene editing to improve salt tolerance in crops.

Hemophagocytic lymphohistiocytosis caused by STAT1 gain-offunction mutation is not driven by interferon-γ:A case report

BACKGROUND Hemophagocytic lymphohistiocytosis(HLH)is a life-threatening hyperinflammatory syndrome caused by many genetic defects.STAT1 is a DNAbinding factor that regulates gene transcription.HLH caused by STAT1 gain-offunction(GOF)mutations has rarely been reported and its clinical manifestations and mechanisms are not clearly defined.CASE SUMMARY A 2-year-old boy presented to our hospital with recurrent fever for>20 d.The patient had a personal history of persistent oral candidiasis and inoculation site infection during the past 2 years.Hepatosplenomegaly was noted.Complete blood cell count showed severe anemia,thrombocytopenia and neutropenia.Other laboratory tests showed liver dysfunction,hypertriglyceridemia and decreased fibrinogen.Hemophagocytosis was found in the bone marrow.Chest computed tomography showed a cavitary lesion.Tests for fungal infection were positive.Serum T helper(Th)1/Th2 cytokine determination demonstrated moderately elevated levels of interleukin(IL)-6 and IL-10 with normal interferon(IFN)-γconcentration.Mycobacterium bovis was identified in bronchoalveolar lavage fluid by polymerase chain reaction.Genetic testing identified a heterozygous mutation of c.1154C>T causing a T385M amino acid substitution in STAT1.Despite antibacterial and antifungal therapy,the febrile disease was not controlled.The signs of HLH were relieved after HLH-94 protocol administration,except fever.Fever was not resolved until he received anti-tuberculosis therapy.Hematopoietic stem cell transplantation was refused and the patient died six months later due to severe pneumonia.CONCLUSION Patients with STAT1 GOF mutation have broad clinical manifestations and may develop HLH.This form of HLH presents with normal IFN-γlevel without cytokine storm.

Both gain-and loss-of-function variants of KCNA1 are associated with paroxysmal kinesigenic dyskinesia

KCNA1 is the coding gene for Kv1.1 voltage-gated potassium-channelαsubunit.Three variants of KCNA1 have been reported to manifest as paroxysmal kinesigenic dyskinesia(PKD),but the correlation between them remains unclear due to the phenotypic complexity of KCNA1 variants as well as the rarity of PKD cases.Using the whole exome sequencing followed by Sanger sequencing,we screen for potential pathogenic KCNA1 variants in patients clinically diagnosed with paroxysmal movement disorders and identify three previously unreported missense variants of KCNA1 in three unrelated Chinese families.The proband of one family(c.496G>A,p.A166T)manifests as episodic ataxia type 1,and the other two(c.877G>A,p.V293I and c.1112C>A,p.T371A)manifest as PKD.The pathogenicity of these variants is confirmed by functional studies,suggesting that p.A166T and p.T371A cause a loss-of-function of the channel,while p.V293I leads to a gain-of-function with the property of voltage-dependent gating and activation kinetic affected.By reviewing the locations of PKD-manifested KCNA1 variants in Kv1.1 protein,we find that these variants tend to cluster around the pore domain,which is similar to epilepsy.Thus,our study strengthens the correlation between KCNA1 variants and PKD and provides more information on genotype–phenotype correlations of KCNA1 channelopathy.

Mutant p53 in colon cancer

The accumulation of genetic alterations in driver genes is responsible for the development and malignant progression of colorectal cancer. Comprehensive genome analyses have revealed the driver genes, including APC, KRAS, TGFBR2, and TP53, whose mutations are frequently found in human colorectal cancers. Among them, the p53 mutation is found in ~60% of colorectal cancers, and a majority of mutations are missense-type at ‘hot spots’, suggesting an oncogenic role of mutant p53 by ‘gain-of-function’ mechanisms. Mouse model studies have shown that one of these missense-type mutations, p53 R270H (corresponding to human R273H), causes submucosal invasion of intestinal tumors, while the loss of wild-type p53 has a limited effect on the invasion process. Furthermore, the same mutant p53 promotes metastasis when combined with Kras activation and TGF-β suppression. Importantly, either missense-type p53 mutation or loss of wild-type p53 induces NF-κB activation by a variety of mechanisms, such as increasing promoter accessibility by chromatin remodeling, which may contribute to progression to epithelial–mesenchymal transition. These results indicate that missense-type p53 mutations together with loss of wild-type p53 accelerate the late stage of colorectal cancer progression through the activation of both oncogenic and inflammatory pathways. Accordingly, the suppression of the mutant p53 function via the inhibition of nuclear accumulation is expected to be an effective strategy against malignant progression of colorectal cancer.

Mutant p53 in cancer therapy-the barrier or the path

Since wild-type p53 is central for maintaining genomic stability and preventing oncogenesis, its coding gene TP53 is highly mutated in ~50% of human cancers, and its activity is almost abrogated in the rest of cancers. Approximately 80% of p53 mutations are single point mutations with several hotspot mutations. Besides loss of function and dominant-negative effect on the wild-type p53 activity, the hotspot p53 mutants also acquire new oncogenic functions, so-called ‘gain-of-functions’(GOF). Because the GOF of mutant p53 is highly associated with late-stage malignance and drug resistance, these p53 mutants have become hot targets for developing novel cancer therapies. In this essay, we review some recent progresses in better understanding of the role of mutant p53 GOF in chemoresistance and the underlying mechanisms, and discuss the pros and cons of targeting mutant p53 for the development of anti-cancer therapies.

Tumor suppressor p53 and metabolism

p53 plays a key role in tumor suppression. The tumor suppressive function of p53 has long been attributed to its ability to induce apoptosis, cell cycle arrest, and senescence in cells. However, recent studies suggest that other functions of p53 also contribute to its role as a tumor suppressor, such as its function in metabolic regulation. p53 regulates various metabolic pathways to maintain the metabolic homeostasis of cells and adapt cells to stress. In addition, recent studies have also shown that gain-offunction (GOF) mutant p53 proteins drive metabolic reprogramming in cancer cells, contributing to cancer progression. Further understanding of p53 and its GOF mutants in metabolism will provide new opportunities for cancer therapy.

The CRISPR/Cas9 revolution continues: From base editing to prime editing in plant science

The ability to precisely inactivate or modify genes in model organisms helps us understand the mysteries of life. Clustered regularly interspaced short palindromic repeats(CRISPR)/CRISPR-associated protein 9(Cas9), a revolutionary technology that could generate targeted mutants, has facilitated notable advances in plant science. Genome editing with CRISPR/Cas9 has gained great popularity and enabled several technical breakthroughs. Herein, we briefly introduce the CRISPR/Cas9, with a focus on the latest breakthroughs in precise genome editing(e.g., base editing and prime editing), and we summarize various platforms that developed to increase the editing efficiency, expand the targeting scope, and improve the specificity of base editing in plants. In addition, we emphasize the recent applications of these technologies to plants. Finally, we predict that CRISPR/Cas9 and CRISPR/Cas9-based genome editing will continue to revolutionize plant science and provide technical support for sustainable agricultural development.