A novel anti-proliferative role of HMGA2 in induction of apoptosis through caspase 2 in primary human fibroblast cells

CircRNAs as upstream regulators of miRNA//HMGA2 axis in human cancer

High mobility group protein A2 (HMGA2) is widely recognized as a chromatin-binding protein, whose overexpression is observed in nearly all human cancers. It exerts its oncogenic effects by influencing various cellular processes such as the epithelial-mesenchymal transition, cell differentiation, and DNA damage repair. MicroRNA (miRNA) serves as a pivotal gene expression regulator, concurrently modulating multiple genes implicated in cancer progression, including HMGA2. It also serves as a significant biomarker for cancer. Circular RNA (circRNA) plays a crucial role in gene regulation primarily by sequestering miRNAs and impeding their ability to enhance the expression of other genes, including HMGA2. Increasingly, studies have underscored the vital role of miRNA/HMGA2 interactions in cancer. Given the significance of circRNA as an upstream regulatory mediator and the complexity of regulatory mechanisms, we hereby present a comprehensive overview of the pivotal role of circRNAs as upstream regulators of the miRNA//HMGA2 axis in human cancers. This insight may herald a novel direction for future cancer research.

Decoding high mobility group A2 protein expression regulation and implications in human cancers

High Mobility Group A2 (HMGA2) oncofetal proteins are a distinct category of Transcription Factors (TFs) known as "architectural factors" due to their lack of direct transcriptional activity. Instead, they modulate the three-dimensional structure of chromatin by binding to AT-rich regions in the minor grooves of DNA through their AT-hooks. This binding allows HMGA2 to interact with other proteins and different regions of DNA, thereby regulating the expression of numerous genes involved in carcinogenesis. Consequently, multiple mechanisms exist to finely control HMGA2 protein expression at various transcriptional levels, ensuring precise concentration adjustments to maintain cellular homeostasis. During embryonic development, HMGA2 protein is highly expressed but becomes absent in adult tissues. However, recent studies have revealed its re-elevation in various cancer types. Extensive research has demonstrated the involvement of HMGA2 protein in carcinogenesis at multiple levels. It intervenes in crucial processes such as cell cycle regulation, apoptosis, angiogenesis, epithelial-to-mesenchymal transition, cancer cell stemness, and DNA damage repair mechanisms, ultimately promoting cancer cell survival. This comprehensive review provides insights into the HMGA2 protein, spanning from the genetic regulation to functional protein behavior. It highlights the significant mechanisms governing HMGA2 gene expression and elucidates the molecular roles of HMGA2 in the carcinogenesis process.

Effects of HMGA2 gene silencing on cell cycle and apoptosis in the metastatic renal carcinoma cell line ACHN

Objective

To explore the role of high mobility group AT-hook 2 (HMGA2) in the regulation of the cell cycle and apoptosis.

Methods

The renal carcinoma cell line ACHN was transiently transfected with small interfering RNA to knock down the expression of the HMGA2 gene. Cell cycle analysis was undertaken using flow cytometry. The mRNA and protein levels of HMGA2, E2F transcription factor 1 (E2F1), cyclin D1, cyclin dependent kinase 6 (CDK6), B-cell lymphoma-2 (Bcl-2), caspase-3 and caspase-9 were analysed using reverse transcription quantitative real-time polymerase chain reaction and Western blot analysis.

Results

The mRNA and protein levels of HMGA2 were significantly higher in renal carcinoma cell lines compared with the human renal proximal tubular epithelial cell line HKC. After HMGA2 gene-specific silencing, more cells entered the G₀/G₁ phase, while fewer cells entered the G₂/M phase; and the cells exhibited early and late apoptosis. HMGA2 gene-specific silencing significantly reduced the mRNA and protein levels of E2F1, cyclin D1, CDK6 and Bcl-2; and increased the mRNA and protein levels of caspase-3 and caspase-9.

Conclusion

The HMGA2 gene may be involved in the tumorigenesis and development of renal cancer, thus inhibiting HMGA2 gene expression might provide a potential therapeutic target in the future.

Silencing of HMGA2 by siRNA Loaded Methotrexate Functionalized Polyamidoamine Dendrimer for Human Breast Cancer Cell Therapy

The transcription factor high mobility group protein A2 (HMGA2) plays an important role in the pathogenesis of some cancers including breast cancer. Polyamidoamine dendrimer generation 4 is a kind of highly branched polymeric nanoparticle with surface charge and highest density peripheral groups that allow ligands or therapeutic agents to attach it, thereby facilitating target delivery. Here, methotrexate (MTX)- modified polyamidoamine dendrimer generation 4 (G4) (G4/MTX) was generated to deliver specific small interface RNA (siRNA) for suppressing HMGA2 expression and the consequent effects on folate receptor (FR) expressing human breast cancer cell lines (MCF-7, MDA-MB-231). We observed that HMGA2 siRNA was electrostatically adsorbed on the surface of the G4/MTX nanocarrier for constructing a G4/MTX-siRNA nano-complex which was verified by changing the final particle size and zeta potential. The release of MTX and siRNA from synthesized nanocomplexes was found in a time- and pH-dependent manner. We know that MTX targets FR. Interestingly, G4/MTX-siRNA demonstrates significant cellular internalization and gene silencing efficacy when compared to the control. Besides, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay demonstrated selective cell cytotoxicity depending on the folate receptor expressing in a dose-dependent manner. The gene silencing and protein downregulation of HMGA2 by G4/MTX-siRNA was observed and could significantly induce cell apoptosis in MCF-7 and MDA-MB-231 cancer cells compared to the control group. Based on the findings, we suggest that the newly developed G4/MTX-siRNA nano-complex may be a promising strategy to increase apoptosis induction through HMGA2 suppression as a therapeutic target in human breast cancer.

HMGA2 as a Critical Regulator in Cancer Development

The high mobility group protein 2 (HMGA2) regulates gene expression by binding to AT-rich regions of DNA. Akin to other DNA architectural proteins, HMGA2 is highly expressed in embryonic stem cells during embryogenesis, while its expression is more limited at later stages of development and in adulthood. Importantly, HMGA2 is re-expressed in nearly all human malignancies, where it promotes tumorigenesis by multiple mechanisms. HMGA2 increases cancer cell proliferation by promoting cell cycle entry and inhibition of apoptosis. In addition, HMGA2 influences different DNA repair mechanisms and promotes epithelial-to-mesenchymal transition by activating signaling via the MAPK/ERK, TGFβ/Smad, PI3K/AKT/mTOR, NFkB, and STAT3 pathways. Moreover, HMGA2 supports a cancer stem cell phenotype and renders cancer cells resistant to chemotherapeutic agents. In this review, we discuss these oncogenic roles of HMGA2 in different types of cancers and propose that HMGA2 may be used for cancer diagnostic, prognostic, and therapeutic purposes.

HMGA Genes and Proteins in Development and Evolution

HMGA (high mobility group A) (HMGA1 and HMGA2) are small non-histone proteins that can bind DNA and modify chromatin state, thus modulating the accessibility of regulatory factors to the DNA and contributing to the overall panorama of gene expression tuning. In general, they are abundantly expressed during embryogenesis, but are downregulated in the adult differentiated tissues. In the present review, we summarize some aspects of their role during development, also dealing with relevant studies that have shed light on their functioning in cell biology and with emerging possible involvement of HMGA1 and HMGA2 in evolutionary biology.

Marked TGF-β-regulated miRNA expression changes in both COPD and control lung fibroblasts

COPD is associated with disturbed tissue repair, possibly due to TGF-β-regulated miRNA changes in fibroblasts. Our aim was to identify TGF-β-regulated miRNAs and their differential regulation and expression in COPD compared to control fibroblasts. Small RNA sequencing was performed on TGF-β-stimulated and unstimulated lung fibroblasts from 15 COPD patients and 15 controls. Linear regression was used to identify TGF-β-regulated and COPD-associated miRNAs. Interaction analysis was performed to compare miRNAs that responded differently to TGF-β in COPD and control. Re-analysis of previously generated Ago2-IP data and Enrichr were used to identify presence and function of potential target genes in the miRNA-targetome of lung fibroblasts. In total, 46 TGF-β-regulated miRNAs were identified in COPD and 86 in control fibroblasts (FDR < 0.05). MiR-27a-5p was the most significantly upregulated miRNA. MiR-148b-3p, miR-589-5p and miR-376b-3p responded differently to TGF-β in COPD compared to control (FDR < 0.25). MiR-660-5p was significantly upregulated in COPD compared to control (FDR < 0.05). Several predicted targets of miR-27a-5p, miR-148b-3p and miR-660-5p were present in the miRNA-targetome, and were mainly involved in the regulation of gene transcription. In conclusion, altered TGF-β-induced miRNA regulation and differential expression of miR-660-5p in COPD fibroblasts, may represent one of the mechanisms underlying aberrant tissue repair and remodelling in COPD.

Identification of differential gene expression in endothelial cells from young and aged mice using RNA-Seq technique

Aging is a complex phenomenon. Endothelial cell senescence is regarded as a vital characteristic of cardiovascular diseases. This study aims to identify differentially expressed genes in vascular endothelial cells (ECs) of different age groups by RNA sequencing (RNA-Seq) technique, and to explore which molecular pathways differentially expressed genes (DEGs) may enrich in. In this study, we used RNA-Seq to analyze DEGs in primary endothelial cells of young and old mice, and further analyzed them by gene ontology (GO) enrichment and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Our results showed that in total identified 229 of the DEGs, 104 were upregulated and 125 were downregulated in endothelial cells of aged mice compared with young mice. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the involvement of these DEGs in the regulation of morphogenesis of a branching structure, angiogenesis, upregulation of cell proliferation, and extracellular matrix (ECM)-receptor interaction. These results provided a novel insight to understand the molecular mechanisms underlying aortic endothelial cell senescence, and some of the novel candidate genes identified in this study may be valuable in elucidating the molecular mechanisms underlying endothelial cell senescence.

Oncological role of HMGA2 (Review)

The high mobility group A2 (HMGA2) protein is a non‑histone architectural transcription factor that modulates the transcription of several genes by binding to AT‑rich sequences in the minor groove of B‑form DNA and alters the chromatin structure. As a result, HMGA2 influences a variety of biological processes, including the cell cycle process, DNA damage repair process, apoptosis, senescence, epithelial‑mesenchymal transition and telomere restoration. In addition, the overexpression of HMGA2 is a feature of malignancy, and its elevated expression in human cancer predicts the efficacy of certain chemotherapeutic agents. Accumulating evidence has suggested that the detection of HMGA2 can be used as a routine procedure in clinical tumour analysis.

CKLF1 aggravates neointimal hyperplasia by inhibiting apoptosis of vascular smooth muscle cells through PI3K/AKT/NF-κB signaling

Chemokine-like factor 1 (CKLF1) is a cytokine, which has a detrimental effect on the multiple disease progression. Our previous studies reported that arterial injury induced the upregulation of CKLF1 expression in artery at 7-14 days after injury. Here, using a rat carotid balloon injury model, we found that CKLF1 knockdown in the injured site abolished neointimal formation and even decreased medial area; contrarily, CKLF1 overexpression developed a thicker neointima than controls, demonstrating that CKLF1 exerted positive effects on neointimal hyperplasia and the accumulation of vascular smooth muscle cells (VSMC). The mechanism study indicated that CKLF1 reduced susceptibility to the cell cycle G2/M arrest and apoptosis, and thereby speeding up VSMC accumulation. This role of CKLF1 was tightly associated with phosphatidylinositol (PI) 3-kinase signaling pathway. CKLF1 increased the expression of four isoforms of the PI3-kinase catalytic subunits, which in turn activated its downstream targets Akt and an effector NF-κB accepted as critical transcription factors of cell survival and proliferation. Furthermore, RNA-sequencing analysis revealed that CKLF1 had wide-ranging roles in regulating the expression of genes that mainly engaged in cell apoptosis and innate immune response. Collectively, the data allow us to conclude that high level CKLF1 after artery injury switches the balance of VSMC proliferation and apoptosis through PI3K/AKT/NF-κB signaling and consequently leads to neointimal hyperplasia. The findings shed insight into new treatment strategies to limit restenosis based on CKLF1 as a future target.

MicroRNA Let-7d-3p Contributes to Cardiac Protection via Targeting HMGA2

We tested the hypothesis that Let-7d-3p contributes to cardiac cell protection during hypoxic challenge. Myoblast H9c2 cells and primary neonatal rat ventricular cardiomyocytes (NRVM) were transfected with five selected miRNA mimics. Both cell lines were subjected to 0.2% oxygen hypoxia. The protective effects of these miRNAs were determined by assessment of cell metabolic activity by CCK8 assay and measurement of lactate dehydrogenase (LDH) release as a marker of cell injury. Apoptosis and autophagy flux were assessed by Annexin V/7-AAD double staining and the ratio of LC3 II/I with Baf-A1 treatment, an autophagy flux inhibitor, respectively. Luciferase-reporter assay, RT-qPCR and Western blots were performed to identify the changes of relevant gene targets. Among five miRNA mimic transfections, Let-7d-3p increased CCK8 activity, and decreased LDH release in both H9c2 and NRVM during hypoxia. Apoptosis was significantly reduced in H9c2 cells transfected with Let-7d-3p mimic. Autophagy and autophagy flux were not affected. In silico, mRNAs of HMGA2, YY1, KLF9, KLF12, and MEX3C are predicted targets for Let-7d-3p. Luciferase-reporter assay confirmed that Let-7d-3p bound directly to the 3’-UTR region of HMGA2, MEX3C, and YY1, the down-regulations of these mRNAs were verified in both H9c2 and NRVM. The protein expression of HMGA2, but not others, was downregulated in H9c2 and NRVM. It is known that HMGA2 is a strong apoptosis trigger through the blocking of DNA repair. Thus, we speculate that the anti-apoptotic effects of Let-7d-3p mimic during hypoxia challenge are due to direct targeting of HMGA2.

HMGA2 and Bach-1 cooperate to promote breast cancer cell malignancy

During breast cancer progression, tumor cells acquire multiple malignant features. The transcription factors and cell cycle regulators high mobility group A2 (HMGA2) and BTB and CNC homology 1 (Bach-1) are overexpressed in several cancers, but the mechanistic understanding of how HMGA2 and Bach-1 promote cancer development has been limited. We found that HMGA2 and Bach-1 are overexpressed in breast cancer tissues and their expression correlates positively in tumors but not in normal tissues. Individual HMGA2 or Bach-1 knockdown downregulates expression of both proteins, suggesting a mutual stabilizing effect between the two proteins. Importantly, combined HMGA2 and Bach-1 knockdown additively decrease cell proliferation, migration, epithelial-to-mesenchymal transition, and colony formation, while promoting apoptotic cell death via upregulation of caspase-3 and caspase-9. First the first time, we show that HMGA2 and Bach-1 overexpression in tumors correlate positively and that the proteins cooperatively suppress a broad range of malignant cellular properties, such as proliferation, migration, clonogenicity, and evasion of apoptotic cell death. Thus, our observations suggest that combined targeting of HMGA2 and Bach1 may be an effective therapeutic strategy to treat breast cancer.

GSK3β activity is essential for senescence-associated heterochromatin foci (SAHF) formation induced by HMGA2 in WI38 cells

Cellular senescence is an irreversible form of cell cycle arrest, which is often characterized by domains of facultative heterochromatin substructures also known as senescence-associated heterochromatin foci (SAHF). SAHF assembly is likely mediated through the downregulation of the Wnt pathway, which inhibits Glycogen Synthase Kinase 3 Beta (GSK3β) in cells undergoing replicative senescence. Alternatively, High Mobility Group AT-Hook 2 (HMGA2) can also induce SAHF formation in primary cells, through a process in which the involved cell signaling pathway is unknown. Accordingly, it is important to determine whether GSK3β and the Wnt pathway are necessary during HMGA2-induced SAHF formation. In this study, we developed a senescence model for SAHF assembly in WI38 cell through ectopic expression of HMGA2. In this model, typical senescent features were identified, including elevated SA-β-galactosidase staining and the downregulation of the Wnt pathway. We also showed that the GSK3β inhibitor LiCl can partly disable SAHF formation through the HMGA2 overexpression in WI38 cells. However, the disabled SAHF formation resulting from the inactivity of GSK3β in our senescence model cannot be restored through ectopic overexpression of Catenin Beta 1 (CTNNB1), a downstream transcription factor of the Wnt pathway. This indicates that the GSK3β activity alone, and not those of downstream target genes, is crucial for the HMGA2-induced SAHF formation following the downregulation of the Wnt pathway.