ING Proteins: Tumour Suppressors or Oncoproteins

Medicago Mting1 Mting2 double knockout mutants are extremely dwarfed and never flower implicating essential MtING functions in growth and flowering

BACKGROUND

Optimal flowering time is critical to agricultural productivity. Despite this, flowering regulation in the Fabaceae (legume) family is not fully understood. For example, FLC and CO control Arabidopsis flowering, but do not regulate flowering in the temperate legume Medicago. Little is known about the genetic roles of the two plant ING genes. They encode proteins with conserved ING and PHD finger domains predicted to function as epigenetic readers. Previously, using CRISPR-Cas9 knock outs, we reported that Medicago MtING2 promotes flowering and growth. However, surprisingly, Mting2 PHD finger mutants flowered similarly to wild type. Additionally, MtING1 did not regulate flowering because Mting1 mutants flowered like wild type.

METHODS

To further dissect the combined genetic function of MtING1 and MtING2 and their PHD fingers, we cross-pollinated Mting1 and Mting2 single mutants to create two double mutants: The Mting1-7 Mting2-2 double knockout mutant and the Mting1-1 Mting2-11 double PHD finger mutant. Mutant phenotypes were assessed in floral-inductive conditions. We used fluorescence confocal microscopy and in vitro protein biophysical analysis to investigate the subcellular localization and oligomerization of the proteins. We carried out gene expression analysis by RNA-seq and RT-qPCR to determine how the two genes affect transcript accumulation to influence growth and flowering.

RESULTS

The Mting double knockout mutants displayed a striking, non-flowering, highly dwarfed phenotype indicating overlapping and complementary functions. Conversely Mting double PHD finger mutants showed only mild dwarfing and weak delays to flowering, indicating that the PHD fingers did not have a major impact on MtING function. MtING proteins localised to the nucleus, consistent with their predicted roles as histone readers, but did not interact in solution. Large changes to gene expression were seen in the Mting2-2 single mutant and the double knockout mutant, with key flowering genes downregulated and predicted floral repressors elevated. Furthermore, the MtINGs promoted the expression of Medicago homologs of target genes of the Arabidopsis NuA4 HAT complex.

CONCLUSIONS

Our findings demonstrate the key combined function the MtING genes play in regulation of global gene expression, flowering time and wider development and implicate an important role in epigenetic regulation via HAT complexes.

Comprehensive analysis of clinical and biological value of ING family genes in liver cancer

BACKGROUND

Liver cancer (LIHC) is a malignant tumor that occurs in the liver and has a high mortality in cancer. The ING family genes were identified as tumor suppressor genes. Dysregulated expression of these genes can lead to cell cycle arrest, senescence and/or apoptosis. ING family genes are promising targets for anticancer therapy. However, their role in LIHC is still not well understood.

AIM

To have a better understanding of the important roles of ING family members in LIHC.

METHODS

A series of bioinformatics approaches (including gene expression analysis, genetic alteration analysis, survival analysis, immune infiltration analysis, prediction of upstream microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) of ING1, and ING1-related gene functional enrichment analysis) was applied to study the expression profile, clinical relationship, prognostic significance and immune infiltration of ING in LIHC. The relationship between ING family genes expression and tumor associated immune checkpoints was investigated in LIHC. The molecular mechanism of ING1 mediated hepatocarcinogenesis was preliminarily discussed.

RESULTS

mRNA/protein expression of different ING family genes in LIHC was analyzed in different databases, showing that ING family genes were highly expressed in LIHC. In 47 samples from 366 LIHC patients, the ING family genes were altered at a rate of 13%. By comprehensively analyzing the expression, clinical pathological parameters and prognostic value of ING family genes, ING1/5 was identified. ING1/5 was related to poor prognosis of LIHC, suggesting that they may play key roles in LIHC tumorigenesis and progression. One of the target miRNAs of ING1 was identified as hsa-miR-214-3p. Two upstream lncRNAs of hsa-miR-214-3p, U91328.1, and HCG17, were identified. At the same time, we found that the expression of ING family genes was correlated with immune cell infiltration and immune checkpoint genes.

CONCLUSION

This study lays a foundation for further research on the potential mechanism and clinical value of ING family genes in the treatment and prognosis of LIHC.

Comprehensive analysis of clinical and biological value of ING family genes in liver cancer

BACKGROUND

Liver cancer (LIHC) is a malignant tumor that occurs in the liver and has a high mortality in cancer. The ING family genes were identified as tumor suppressor genes. Dysregulated expression of these genes can lead to cell cycle arrest, senescence and/or apoptosis. ING family genes are promising targets for anticancer therapy. However, their role in LIHC is still not well understood.

AIM

To have a better understanding of the important roles of ING family members in LIHC.

METHODS

A series of bioinformatics approaches (including gene expression analysis, genetic alteration analysis, survival analysis, immune infiltration analysis, prediction of upstream microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) of ING1, and ING1-related gene functional enrichment analysis) was applied to study the expression profile, clinical relationship, prognostic significance and immune infiltration of ING in LIHC. The relationship between ING family genes expression and tumor associated immune checkpoints was investigated in LIHC. The molecular mechanism of ING1 mediated hepatocarcinogenesis was preliminarily discussed.

RESULTS

mRNA/protein expression of different ING family genes in LIHC was analyzed in different databases, showing that ING family genes were highly expressed in LIHC. In 47 samples from 366 LIHC patients, the ING family genes were altered at a rate of 13%. By comprehensively analyzing the expression, clinical pathological parameters and prognostic value of ING family genes, ING1/5 was identified. ING1/5 was related to poor prognosis of LIHC, suggesting that they may play key roles in LIHC tumorigenesis and progression. One of the target miRNAs of ING1 was identified as hsa-miR-214-3p. Two upstream lncRNAs of hsa-miR-214-3p, U91328.1, and HCG17, were identified. At the same time, we found that the expression of ING family genes was correlated with immune cell infiltration and immune checkpoint genes.

CONCLUSION

This study lays a foundation for further research on the potential mechanism and clinical value of ING family genes in the treatment and prognosis of LIHC.

Deciphering the dual roles of PHD finger proteins from oncogenic drivers to tumor suppressors

PHD (plant homeodomain) finger proteins emerge as central epigenetic readers and modulators in cancer biology, orchestrating a broad spectrum of cellular processes pivotal to oncogenesis and tumor suppression. This review delineates the dualistic roles of PHD fingers in cancer, highlighting their involvement in chromatin remodeling, gene expression regulation, and interactions with cellular signaling networks. PHD fingers' ability to interpret specific histone modifications underscores their influence on gene expression patterns, impacting crucial cancer-related processes such as cell proliferation, DNA repair, and apoptosis. The review delves into the oncogenic potential of certain PHD finger proteins, exemplified by PHF1 and PHF8, which promote tumor progression through epigenetic dysregulation and modulation of signaling pathways like Wnt and TGFβ. Conversely, it discusses the tumor-suppressive functions of PHD finger proteins, such as PHF2 and members of the ING family, which uphold genomic stability and inhibit tumor growth through their interactions with chromatin and transcriptional regulators. Additionally, the review explores the therapeutic potential of targeting PHD finger proteins in cancer treatment, considering their pivotal roles in regulating cancer stem cells and influencing the immune response to cancer therapy. Through a comprehensive synthesis of current insights, this review underscores the complex but promising landscape of PHD finger proteins in cancer biology, advocating for further research to unlock novel therapeutic avenues that leverage their unique cellular roles.

The chromatin reader protein ING5 is required for normal hematopoietic cell numbers in the fetal liver

ING5 is a component of KAT6A and KAT7 histone lysine acetylation protein complexes. ING5 contains a PHD domain that binds to histone H3 lysine 4 when it is trimethylated, and so functions as a 'reader' and adaptor protein. KAT6A and KAT7 function are critical for normal hematopoiesis. To examine the function of ING5 in hematopoiesis, we generated a null allele of Ing5. Mice lacking ING5 during development had decreased foetal liver cellularity, decreased numbers of hematopoietic stem cells and perturbed erythropoiesis compared to wild-type control mice. Ing5^-/- pups had hypoplastic spleens. Competitive transplantation experiments using foetal liver hematopoietic cells showed that there was no defect in long-term repopulating capacity of stem cells lacking ING5, suggesting that the defects during the foetal stage were not cell intrinsic. Together, these results suggest that ING5 function is dispensable for normal hematopoiesis but may be required for timely foetal hematopoiesis in a cell-extrinsic manner.

Structural analysis of ING3 protein and histone H3 binding

Proteins belonging to the ING family regulate the transcriptional state of chromatin by recruiting remodeling complexes to sites with histone H3 trimethylated at Lysine 4 (H3K4me3). This modification is recognized by the Plant HomeoDomain (PHD) present at the C-terminal region of the five ING proteins. ING3 facilitates acetylation of histones H2A and H4 by the NuA4-Tip60 MYST histone acetyl transferase complex, and it has been proposed to be an oncoprotein. The crystal structure of the N-terminal domain of ING3 shows that it forms homodimers with an antiparallel coiled-coil fold. The crystal structure of the PHD is similar to those of its four homologs. These structures explain the possible deleterious effects of ING3 mutations detected in tumors. The PHD binds histone H3K4me3 with low-micromolar, and binds the non-methylated histone with a 54-fold reduced affinity. Our structure explains the impact of site directed mutagenesis experiments on histone recognition. These structural features could not be confirmed for the full-length protein as solubility was insufficient for structural studies, but the structure of its folded domains suggest a conserved structural organization for the ING proteins as homodimers and bivalent readers of the histone H3K4me3 mark.

Analysis of patients with colorectal cancer shows a specific increase in serum anti-ING1 autoantibody levels

Colorectal cancer (CRC) is the third most prevalent cancer in the world, yet the sensitivity and specificity of biomarkers for CRC diagnosis are insufficient. In the present study, we performed a protein microarray screening method to identify antibody markers for CRC. Inhibitor of growth family 1 (ING1) was identified as a candidate tumor antigen for CRC using protein microarrays (ProtoArray). Subsequent amplified luminescence proximity homogeneous assay-linked immunosorbent assay using recombinant ING1 protein showed that the serum levels of anti-ING1 antibodies were increased not only in patients with CRC but also in those with esophageal cancer (EC), gastric cancer (GC), breast cancer (BrC), and pancreatic cancer (PC) compared with those of healthy donors (HDs). Antibodies against the ING1 amino acids between 239 and 253 were present at significantly higher levels in patients with CRC than in those with EC, GC, BrC, or PC. Anti-ING1 antibody levels were significantly higher in the patients with CRC at any stages than in the HDs. Immunohistochemical staining revealed higher expression of ING1 protein in CRC cells than in the adjacent normal tissues. In luciferase reporter assays using a CRC cell line, ING1 augmented p53-mediated NOXA promoter activity but attenuated p53-stimulated Bax, p21, and PUMA promoter activities. Consequently, serum anti-ING1 antibodies can be used for sensitive and specific diagnoses of CRC.

In silico analysis prediction of HepTH1-5 as a potential therapeutic agent by targeting tumour suppressor protein networks

Many studies reported that the activation of tumour suppressor protein, p53 induced the human hepcidin expression. However, its expression decreased when p53 was silenced in human hepatoma cells. Contrary to Tilapia hepcidin TH1-5, HepTH1-5 was previously reported to trigger the p53 activation through the molecular docking approach. The INhibitor of Growth (ING) family members are also shown to directly interact with p53 and promote cell cycle arrest, senescence, apoptosis and participate in DNA replication and DNA damage responses to suppress the tumour initiation and progression. However, the interrelation between INGs and HepTH1-5 remains unknown. Therefore, this study aims to identify the mechanism and their protein interactions using in silico approaches. The finding revealed that HepTH1-5 and its ligands had interacted mostly on hotspot residues of ING proteins which involved in histone modifications via acetylation, phosphorylation, and methylation. This proves that HepTH1-5 might implicate in an apoptosis signalling pathway and preserve the protein structure and function of INGs by reducing the perturbation of histone binding upon oxidative stress response. This study would provide theoretical guidance for the design and experimental studies to decipher the role of HepTH1-5 as a potential therapeutic agent for cancer therapy. Communicated by Ramaswamy H. Sarma.

An in silico study of how histone tail conformation affects the binding affinity of ING family proteins

Background

Due to its intrinsically disordered nature, the histone tail is conformationally heterogenic. Therefore, it provides specific binding sites for different binding proteins or factors through reversible post-translational modifications (PTMs). For instance, experimental studies stated that the ING family binds with the histone tail that has methylation on the lysine in position 4. However, numerous complexes featuring a methylated fourth lysine residue of the histone tail can be found in the UniProt database. So the question arose if other factors like the conformation of the histone tail affect the binding affinity.

Methods

The crystal structure of the PHD finger domain from the proteins ING1, ING2, ING4, and ING5 are docked to four histone H3 tails with two different conformations using Haddock 2.4 and ClusPro. The best four models for each combination are selected and a two-sample t-test is performed to compare the binding affinities of helical conformations vs. linear conformations using Prodigy. The protein-protein interactions are examined using LigPlot.

Results

The linear histone conformations in predicted INGs-histone H3 complexes exhibit statistically significant higher binding affinity than their helical counterparts (confidence level of 99%). The outputs of predicted models generated by the molecular docking programs Haddock 2.4 and ClusPro are comparable, and the obtained protein-protein interaction patterns are consistent with experimentally confirmed binding patterns.

Conclusion

The results show that the conformation of the histone tail is significantly affecting the binding affinity of the docking protein. Herewith, this in silico study demonstrated in detail the binding preference of the ING protein family to histone H3 tail. Further research on the effect of certain PTMs on the final tail conformation and the interaction between those factors seem to be promising for a better understanding of epigenetics.