Inhibitor of Growth 4 (ING4) is a positive regulator of rRNA synthesis

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.

Ing4-deficiency promotes a quiescent yet transcriptionally poised state in hematopoietic stem cells

Defining the mechanisms that regulate stem cell maintenance, proliferation, and differentiation is critical for identifying therapies for improving stem cell function under stress. Here, we have identified the tumor suppressor, inhibitor of growth 4 (Ing4), as a critical regulator of hematopoietic stem cell (HSC) homeostasis. Cancer cell line models with Ing4 deficiency have shown that Ing4 functions as a tumor suppressor, in part, due to Ing4-mediated regulation of several major signaling pathways, including c-Myc. In HSCs, we show Ing4 deficiency promotes gene expression signatures associated with activation, yet HSCs are arrested in G0, expressing several markers of quiescence. Functionally, Ing4-deficient HSCs demonstrate robust regenerative capacity following transplantation. Our findings suggest Ing4 deficiency promotes a poised state in HSCs, where they appear transcriptionally primed for activation but remain in a resting state. Our model provides key tools for further identification and characterization of pathways that control quiescence and self-renewal in HSCs.

Newly identified tumor suppressor functions of ING proteins

The INhibitor of Growth (ING) proteins (ING1, ING2, ING3, ING4 and ING5) are a family of epigenetic regulators. Their decreased expression in numerous cancers led to identifying the ING proteins as gatekeeper tumor suppressors as they regulate cell cycle progression, apoptosis and senescence. Subsequently, they were also described as caretaker tumor suppressors through their involvement in DNA replication and the DNA damage response (DDR). Recent studies have identified new interactions of the ING proteins with proteins or pathways implicated in cell proliferation, the maintenance of stem cells pluripotency or the DDR. Furthermore, the ING proteins have been identified as regulators of ribosomal RNA synthesis and of mRNA stability and as regulators of mitochondrial DNA transcription resulting in the regulation of metabolism. These new findings highlight new antitumorigenic activities of the ING proteins that are potential targets for cancer treatment.

Inhibitor of Growth Factors Regulate Cellular Senescence

Simple Summary

Five members of the Inhibitor of Growth (ING) family share a highly conserved plant homeodomian with affinity to the specific histone modification H3K4me3. Since some ING family members are preferentially associated with histone acetyltransferaseactivity while other members with histone deacetlyse activity, the ING family membres are epigenetic regulators. Interestingly, ING members can regulate the induction cellular senescence in both primray untransformed human cells as well as human cancer cells. We discuss here the up-to-date knowledge about their regulatory activity within the cellular senescent program.

Abstract

The Inhibitor of Growth (ING) proteins are a group of tumor suppressors with five conserved genes. A common motif of ING factors is the conserved plant homeodomain (PHD), with which they bind to chromatin as readers of the histone mark trimethylated histone H3 (H3K4me3). These genes often produce several protein products through alternative splicing events. Interestingly, ING1 and ING2 participate in the establishment of the repressive mSIN3a-HDAC complexes, whereas ING3, ING4, and ING5 are associated with the activating HAT protein complexes. In addition to the modulation of chromatin’s structure, they regulate cell cycle transition, cellular senescence, repair of DNA damage, apoptosis, and angiogenic pathways. They also have fundamental effects on regulating cellular senescence in cancer cells. In the current review, we explain their role in cellular senescence based on the evidence obtained from cell line and animal studies, particularly in the context of cancer.

ING4 Promotes Stemness Enrichment of Human Renal Cell Carcinoma Cells Through Inhibiting DUSP4 Expression to Activate the p38 MAPK/type I IFN-Stimulated Gene Signaling Pathway

Renal cell carcinoma (RCC) recurs frequently due to high metastatic spread, resulting in a high mortality. Cancer stem cells play a critical role in initiating the tumor metastasis. Inhibitor of growth 4 (ING4) is a member of the ING family, but its impact on cancer stem cells in RCC is still unknown. In this study, we found that ING4 significantly promoted the sphere-forming size and number of RCC cells under an ultralow-attachment culture condition in vitro, tumor growth and metastasis in vivo, and the expression of some stem-like or pluripotent biomarkers CD44, MYC, OCT4, and NANOG, indicating that ING4 increased the stemness enrichment of RCC cells. Mechanistically, the ING4-activated p38 MAPK pathway possibly upregulated the expression of type I IFN-stimulated genes to promote the formation of RCC stem cells. ING4 could inhibit the expression of DUSP4 to activate p38 MAPK. In addition, selective pharmacological p38 MAPK inhibitors could significantly inhibit stemness enrichment only in ING4-overexpressed RCC cells, suggesting that the p38 MAPK inhibitors might be effective in patients with high ING4 expression in RCC tissue. Taken together, our findings proposed that ING4 might serve as a potential therapeutic target for metastatic RCC, particularly RCC stem cells.

Correlation analysis of survivin, ING4, CXCL8 and VEGF expression in prostate cancer tissue

OBJECTIVE

This study aimed to investigate the expression of Survivin, inhibitor of growth 4 (ING4), CXC chemokine ligand 8 (CXCL8), vascular endothelial growth factor (VEGF), and the correlation between Survivin, ING4, CXCL8 and VEGF in prostate cancer (PCa) tissues.

METHODS

From January 2019 to December 2019, 51 patients from Chengwu People's Hospital and The First People's Hospital of Taian, with PCa were selected as the PCa group and 47 patients with benign prostatic hyperplasia (BPH) were included as the BPH group. The expression of Survivin, ING4, CXCL8 and VEGF in both groups and among patients with different clinical stages in the PCa group were compared, and the correlation between Survivin, ING4, CXCL8 and VEGF expression in PCa tissues was analyzed.

RESULTS

Survivin, ING4, CXCL8, and VEGF expression differed significantly between the two groups (P<0.05). The Survivin positive expression rate, CXCL8 positive expression rate, and VEGF positive expression rate in the PCa group were significantly higher than those in the BPH group (P<0.05), and ING4 positive expression rate in the PCa group was significantly lower than that in the BPH group (P<0.05). Survivin positive expression rate, CXCL8 positive expression rate, and VEGF positive expression rate were significantly higher in PCa patients with stage III+IV than those of stage I+II (P<0.05), and ING4 positive expression rate in PCa patients in stage III+IV was significantly lower than that in stage I+II (P<0.05). Kendall's tau-b analysis, VEGF was positively correlated with Survivin and CXCL8 (P<0.05) and negatively correlated with ING4 (P<0.05) in PCa tissues.

CONCLUSION

Survivin, CXCL8, and VEGF were highly expressed and ING4 was lowly expressed in PCa tissues, which was correlated with clinical stage; additionally, Survivin, ING4, CXCL8, and VEGF played a synergistic role with each other in the development and progression of PCa.

ING3 and ING4 immunoexpression and their relation to the development of benign odontogenic lesions

The Inhibitor of Growth (ING) gene family is a group of tumor suppressor genes that play important roles in cell cycle control, senescence, DNA repair, cell proliferation, and apoptosis. However, inactivation and downregulation of these proteins have been related in some neoplasms. The present study aimed to evaluate the immunohistochemical profiles of ING3 and ING4 proteins in a series of benign epithelial odontogenic lesions.

METHODS

The sample comprised of 20 odontogenic keratocysts (OKC), 20 ameloblastomas (AM), and 15 adenomatoid odontogenic tumors (AOT) specimens. Nuclear and cytoplasmic immunolabeling of ING3 and ING4 were semi-quantitatively evaluated in epithelial cells of the odontogenic lesions, according to the percentage of immunolabelled cells in each case. Descriptive and statistics analysis were computed, and the p-value was set at 0.05.

RESULTS

No statistically significant differences were found in cytoplasmic and nuclear ING3 immunolabeling among the studied lesions. In contrast, AOTs presented higher cytoplasmic and nuclear ING4 labeling compared to AMs (cytoplasmic p-value = 0.01; nuclear p-value < 0.001) and OKCs (nuclear p-value = 0.007).

CONCLUSION

ING3 and ING4 protein downregulation may play an important role in the initiation and progression of more aggressive odontogenic lesions, such as AMs and OKCs.

Cell-Penetrating Peptides Predicted From CASC3, AKIP1, and AHRR Proteins

Peptides can be used as research tools and for diagnostic or therapeutic applications. Peptides, alongside small molecules and antibodies, are used and are gaining further interest as protein-protein interaction (PPI) modulators. Peptides have high target specificity and high affinity, but, unlike small molecule modulators, they are not able to cross the cell membranes to reach their intracellular targets. To overcome this limitation, the special property of the cell-penetrating peptides (CPPs) could benefit their cause. CPPs are a class of peptides that can enter the cells and with them also deliver the attached cargoes. Today, with the advancement of in silico prediction tools and the availability of protein databases, designing new and multifunctional peptides that are able to reach intracellular targets and inhibit certain cellular processes in a very specific manner is reachable. Although there are several efficient CPP sequences already known, the discovery of new CPPs is crucial for the development of efficient delivery methods for both biotechnological and therapeutic applications. In this work, we chose 10 human nuclear proteins from which we predicted new potential CPP sequences by using three different CPP predictors: cell-penetrating peptide prediction tool, CellPPD, and SkipCPP-Pred. From each protein, one predicted CPP sequence was synthesized and its internalization into cells was assessed. Out of the tested sequences, three peptides displayed features characteristic to CPPs. These peptides and also the predicted peptide sequences could be used to design and modify new CPPs. In this work, we show that we can use protein sequences as input for generating new peptides with cell internalization properties. Three new CPPs, AHRR_8-24, CASC3_251-264, and AKIP1_27-37, can be further used for the delivery of other cargoes or designed into multifunctional peptides with capability of internalizing cells.

Antagonising Chromatin Remodelling Activities in the Regulation of Mammalian Ribosomal Transcription

Ribosomal transcription constitutes the major energy consuming process in cells and is regulated in response to proliferation, differentiation and metabolic conditions by several signalling pathways. These act on the transcription machinery but also on chromatin factors and ncRNA. The many ribosomal gene repeats are organised in a number of different chromatin states; active, poised, pseudosilent and repressed gene repeats. Some of these chromatin states are unique to the 47rRNA gene repeat and do not occur at other locations in the genome, such as the active state organised with the HMG protein UBF whereas other chromatin state are nucleosomal, harbouring both active and inactive histone marks. The number of repeats in a certain state varies on developmental stage and cell type; embryonic cells have more rRNA gene repeats organised in an open chromatin state, which is replaced by heterochromatin during differentiation, establishing different states depending on cell type. The 47S rRNA gene transcription is regulated in different ways depending on stimulus and chromatin state of individual gene repeats. This review will discuss the present knowledge about factors involved, such as chromatin remodelling factors NuRD, NoRC, CSB, B-WICH, histone modifying enzymes and histone chaperones, in altering gene expression and switching chromatin states in proliferation, differentiation, metabolic changes and stress responses.

ING Proteins: Tumour Suppressors or Oncoproteins

The INhibitor of Growth family was defined in the mid-1990s by the identification of a tumour suppressor, ING1, and subsequent expansion of the family based essentially on sequence similarities. However, later work and more recent investigations demonstrate that at least a few ING proteins are actually required for normal proliferation of eukaryotic cells, from yeast to human. ING proteins are also part of a larger family of chromatin-associated factors marked by a plant homeodomain (PHD), which mediates interactions with methylated lysine residues. Herein, we discuss the role of ING proteins and their various roles in chromatin signalling in the context of cancer development and progression.