Intracellular distribution of HMG1, HMG2 and UBF change following treatment with cisplatin

The transcription factor HMGB2 indirectly regulates APRIL expression and Gd-IgA1 production in patients with IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Proliferation-inducing ligand (APRIL) was identified as an important cause of glycosylation deficiency of IgA1 (Gd-IgA1), which can 'trigger' IgAN. Our previous study indicated that high migration group protein B2 (HMGB2) in peripheral blood mononuclear cells from patients with IgAN was associated with disease severity, but the underlying mechanism remains unclear.

MATERIALS AND METHODS

The location of HMGB2 was identified by immunofluorescence. qRT-PCR and Western blotting were used to measure HMGB2, HMGA1, and APRIL expression. Gd-IgA1 levels were detected by enzyme-linked immunosorbent assay (ELISA). In addition, we used DNA pull-down, protein profiling, and transcription factor prediction software to identify proteins bound to the promoter region of the APRIL gene. RNA interference and coimmunoprecipitation (Co-IP) were used to verify the relationships among HMGB2, high mobility group AT-hook protein 1 (HMGA1), and APRIL.

RESULTS

HMGB2 expression was greater in IgAN patients than in HCs and was positively associated with APRIL expression in B cells. DNA pull-down and protein profiling revealed that HMGB2 and HMGA1 bound to the promoter region of the APRIL gene. The expression levels of HMGA1, APRIL, and Gd-IgA1 were downregulated after HMGB2 knockdown. Co-IP indicated that HMGB2 binds to HMGA1. The Gd-IgA1 concentration in the supernatant was reduced after HMGA1 knockdown. HMGA1 binding sites were predicted in the promoter region of the APRIL gene.

CONCLUSION

HMGB2 expression is greater in IgAN patients than in healthy controls; it promotes APRIL expression by interacting with HMGA1, thereby inducing Gd-IgA1 overexpression and leading to IgAN.

Human NTHL1 expression and subcellular distribution determines cisplatin sensitivity in human lung epithelial and non-small cell lung cancer cells

Base excision repair is critical for maintaining genomic stability and for preventing malignant transformation. NTHL1 is a bifunctional DNA glycosylase/AP lyase that initiates repair of oxidatively damaged pyrimidines. Our recent work established that transient over-expression of NTHL1 leads to acquisition of several hallmarks of cancer in non-tumorigenic immortalized cells likely through interaction with nucleotide excision repair protein XPG. Here, we investigate how NTHL1 expression levels impact cellular sensitivity to cisplatin in non-tumorigenic immortalized cells and five non-small cell lung carcinomas cell lines. The cell line with lowest expression of NTHL1 (H522) shows the highest resistance to cisplatin indicating that decrease in NTHL1 levels may modulate resistance to crosslinking agents in NSCLC tumors. In a complementation study, overexpression of NTHL1 in H522 cell line sensitized it to cisplatin. Using NTHL1 N-terminal deletion mutants defective in nuclear localization we show that cisplatin treatment can alter NTHL1 subcellular localization possibly leading to altered protein-protein interactions and affecting cisplatin sensitivity. Experiments presented in this study reveal a previously unknown link between NTHL1 expression levels and cisplatin sensitivity of NSCLC tumor cells. These findings provide an opportunity to understand how altered NTHL1 expression levels and subcellular distribution can impact cisplatin sensitivity in NSCLC tumor cells.

Structure and Functions of HMGB2 Protein

High-Mobility Group (HMG) chromosomal proteins are the most numerous nuclear non-histone proteins. HMGB domain proteins are the most abundant and well-studied HMG proteins. They are involved in variety of biological processes. HMGB1 and HMGB2 were the first members of HMGB-family to be discovered and are found in all studied eukaryotes. Despite the high degree of homology, HMGB1 and HMGB2 proteins differ from each other both in structure and functions. In contrast to HMGB2, there is a large pool of works devoted to the HMGB1 protein whose structure-function properties have been described in detail in our previous review in 2020. In this review, we attempted to bring together diverse data about the structure and functions of the HMGB2 protein. The review also describes post-translational modifications of the HMGB2 protein and its role in the development of a number of diseases. Particular attention is paid to its interaction with various targets, including DNA and protein partners. The influence of the level of HMGB2 expression on various processes associated with cell differentiation and aging and its ability to mediate the differentiation of embryonic and adult stem cells are also discussed.

Biological functions and theranostic potential of HMGB family members in human cancers

The high mobility group box (HMGB) protein family consists of four members: HMGB1, 2, 3, and 4. They share similar amino acid sequences and identical functional regions, especially HMGB1, 2, and 3. The homology in structure may lead to similarity in function. In fact, though their targets may be different, they all possess the fundamental function of binding and distorting target DNAs. However, further research confirmed they are distributed differently in tissues and involved in various distinct physiological and pathological cellular processes, including cell proliferation, division, migration, and differentiation. Recently, the roles of HMGB family members in carcinogenesis has been widely investigated; however, systematic discussion on their functions and clinical values in malignant tumors is limited. In this review, we mainly review and summarize recent advances in knowledge of HMGB family members in terms of structure, distribution, biochemical cascades, and specific mechanisms regarding tumor progression. Importantly, the diagnostic, prognostic, and therapeutic value of these proteins in cancers is discussed. Finally, we envisage the orientation and challenges of this field in further studies.

Depletion of the cisplatin targeted HMGB-box factor UBF selectively induces p53-independent apoptotic death in transformed cells

Cisplatin-DNA adducts act as strong decoys for the Upstream Binding Factor UBF (UBTF) and have been shown to inhibit transcription of the ribosomal RNA genes by RNA polymerase I. However, it is unclear if this plays a significant role in the chemotherapeutic activity of cis- or carboplatin. We find that cisplatin in fact induces a very rapid displacement of UBF from the ribosomal RNA genes and strong inhibition of ribosomal RNA synthesis, consistent with this being an important factor in its cytotoxicity. Using conditional gene deletion, we recently showed that UBF is an essential factor for transcription of the ribosomal RNA genes and for ribosome biogenesis. We now show that loss of UBF arrests cell proliferation and induces fully penetrant, rapid and synchronous apoptosis, as well as nuclear disruption and cell death, specifically in cells subjected to oncogenic stress. Apoptosis is not affected by homozygous deletion of the p53 gene and occurs equally in cells transformed by SV40 T antigens, by Myc or by a combination of Ras & Myc oncogenes. The data strongly argue that inhibition of UBF function is a major factor in the cytotoxicity of cisplatin. Hence, drug targeting of UBF may be a preferable approach to the use of the highly toxic platins in cancer therapy.

The RNA polymerase I transcription machinery: an emerging target for the treatment of cancer

The RNA polymerase I (Pol I) transcription machinery in the nucleolus is the key convergence point that collects and integrates a vast array of information from cellular signaling cascades to regulate ribosome production that in turn guides cell growth and proliferation. Cancer cells commonly harbor mutations that inactivate tumor suppressors, hyperactivate oncogenes, and upregulate protein kinases, all of which promote Pol I transcription and drive cell proliferation. The intimate balance between Pol I transcription and growth-factor signaling is perturbed in cancer cells, indicating that upregulation of rRNA synthesis is mandatory for all tumors. Though the emerging picture of transcriptional regulation reveals an unexpected level of complexity, we are beginning to understand the multiple links between rRNA biogenesis and cancer. In this review, we discuss experimental data and potential strategies to downregulate rRNA synthesis and induce an antiproliferative response in cancer cells.

Involvement of high mobility group B proteins in cisplatin-induced cytotoxicity in squamous cell carcinoma of skin

Cis-diamminedichloroplatinum (II) (cisplatin) is a well-known anticancer drug with high potency and efficacy against various types of human cancers. Although it is widely accepted that the mechanism of cisplatin action is via apoptosis, there is enough evidence to support that cisplatin-induced cell death also occurs by other nonapoptotic pathways. Nonhistone, high mobility group (HMG) proteins are known to bind cisplatin-damaged DNA, and we studied their expression during cisplatin-induced cell death using immunohistochemistry, Western blot, and RT-PCR. Results show that the cell death is primarily apoptotic during initial stages of cisplatin treatment of skin tumors, and there is only marginal increase in high mobility group B (HMGB) levels, indicating that HMGB are still bound to nucleus. However, extended treatment of skin tumors with cisplatin caused necrosis and showed significantly increased levels of HMGB, which suggests that HMGB thus released from nuclei act as cytokine and trigger inflammatory response leading to necrosis. Present results clearly indicate a strong association between HMGB proteins and cisplatin-induced cell death that is dominantly apoptotic or necrotic depending on the duration of cisplatin exposure. Because of their important implication in the outcome of cancer chemotherapy, HMGB proteins can be interesting therapeutic targets.

Overexpression of high mobility group (HMG) B1 and B2 proteins directly correlates with the progression of squamous cell carcinoma in skin

High mobility group B (HMGB) chromosomal proteins, which plays important role in cancer and inflammation, were followed at various stages of the squamous cell carcinoma of skin. Present results were analyzed by histopathology, BrdU assay, immunohistochemistry, western blot and RT-PCR, which indicate that at early stages of tumorigenesis, expression of HMGB (B1, B2), raised only by about 20%. However, the advanced (> or =12 weeks) tumors showed significant (> or =80%) increase in HMG levels. Using skin cancer model, we demonstrated that high levels of HMGB directly correlate with the extent of neoplastic changes, and it appears that HMGB is an effective stimulus for cell differentiation, tumor progression, and metastatic invasion.

The grateful dead: damage-associated molecular pattern molecules and reduction/oxidation regulate immunity

The response to pathogens and damage in plants and animals involves a series of carefully orchestrated, highly evolved, molecular mechanisms resulting in pathogen resistance and wound healing. In metazoans, damage- or pathogen-associated molecular pattern molecules (DAMPs, PAMPs) execute precise intracellular tasks and are also able to exert disparate functions when released into the extracellular space. The emergent consequence for both inflammation and wound healing of the abnormal extracellular persistence of these factors may underlie many clinical disorders. DAMPs/PAMPs are recognized by hereditable receptors including the Toll-like receptors, the NOD1-like receptors and retinoic-acid-inducible gene I-like receptors, as well as the receptor for advanced glycation end products. These host molecules 'sense' not only pathogens but also misfolded/glycated proteins or exposed hydrophobic portions of molecules, activating intracellular cascades that lead to an inflammatory response. Equally important are means to not only respond to these molecules but also to eradicate them. We have speculated that their destruction through oxidative mechanisms normally exerted by myeloid cells, such as neutrophils and eosinophils, or their persistence in the setting of pathologic extracellular reducing environments, maintained by exuberant necrotic cell death and/or oxidoreductases, represent important molecular means enabling chronic inflammatory states.

Interaction with p53 enhances binding of cisplatin-modified DNA by high mobility group 1 protein

A nonhistone chromosomal protein, high mobility group (HMG) 1, is ubiquitous in higher eukaryotic cells and binds preferentially to cisplatin-modified DNA. HMG1 also functions as a coactivator of p53, a tumor suppressor protein. We investigated physical interactions between HMG1 and p53 and the influence of p53 on the ability of HMG1 to recognize damaged DNA. Using immunochemical coprecipitation, we observed binding of HMG1 and p53. Interaction between HMG1 and p53 required the HMG A box of HMG1 and amino acids 363-376 of p53. Cisplatin-modified DNA binding by HMG1 was significantly enhanced by p53. An HMG1-specific antibody that recognized the A box of this protein also stimulated cisplatin-modified DNA binding. These data suggest that an interaction with either p53 or antibody may induce conformational change in the HMG1 A box that optimizes DNA binding by HMG1. Interaction of p53 with HMG1 after DNA damage may promote activation of specific HMG1 binding to damaged DNA in vivo and provide a molecular link between DNA damage and p53-mediated DNA repair.

Extracellular matrix and nuclear localization of beta ig-h3 in human bladder smooth muscle and fibroblast cells

The extracellular matrix (ECM) plays an essential role in bladder structure and function. In this study, expression of beta ig-h3, a recently identified extracellular matrix protein, was investigated in human bladder tissue, and human bladder smooth-muscle (SMC) and fibroblast cells in vitro. SMCs secreted greater than three times the level of this protein compared with fibroblasts. The relative levels of beta ig-h3 mRNA in the two cell types reflected the protein expression. Immunohistochemical analysis demonstrated protein deposition in the ECM as well as cytoplasmic localization and, unexpectedly, nuclei. Anti-beta ig-h3 antibodies also stained the matrix surrounding the detrusor SMCs and nuclei of bladder fibroblasts, SMCs, and urothelium in intact bladder tissue. Western blot analyses of medium and matrix fractions obtained from cells in vitro revealed protein of approximately 70-74 kDa, whereas nuclear extracts contained a 65-kDa reactive protein band. We propose that although this protein is a structural component of bladder ECM, its nuclear localization suggests that it has other regulatory and/or structural functions.

Cisplatin inhibits synthesis of ribosomal RNA in vivo

Cis -diammininedichloroplatinum(II) (cisplatin or cis -DDP) is a DNA-damaging agent that is widely used in cancer chemotherapy. Cisplatin crosslinks DNA and the resulting adducts interact with proteins that contain high-mobility-group (HMG) domains, such as UBF(upstream binding factor). UBF is a transcription factor that binds to the promoter of ribosomal RNA (rRNA) genes thereby supporting initiation of transcription by RNA polymerase I. Here we report that cisplatin causes a redistribution of UBF in the nucleolus of human cells, similar to that observed after inhibition of rRNA synthesis. A similar redistribution was observed for the major components of the rRNA transcription machinery, namely TBP, TAFIs and RNA polymerase I. Furthermore, we provide for the first time direct in vivo evidence that cisplatin blocks synthesis of rRNA, while activity of RNA polymerase II continues to be detected throughout the nucleus. The clinically ineffective trans isomer (trans -DDP) does not alter the localization of either UBF or other components of the RNA polymerase I transcription machinery. These results suggest that disruption of rRNA synthesis, which is stimulated in proliferating cells, plays an important role in the clinical success of cisplatin.

High-mobility group 1 protein inhibits helicase catalyzed displacement of cisplatin-damaged DNA

We have determined the effect of HMG-1 bound to cisplatin-damaged DNA on the activities of calf helicase E. DNase I protection analysis demonstrated HMG-1 bound a cisplatin-damaged 24 base oligonucleotide annealed to M13mp18. Exonuclease digestion experiments revealed that greater than 90% of the DNA substrates contained a single site specific cisplatin adduct and, maximally, 65% of the substrates were bound by HMG-1. Helicase E catalyzed displacement of the cisplatin-damaged DNA oligonucleotide was inhibited by HMG-1 in a concentration-dependent manner. Time course experiments revealed a decreased rate of displacement in reactions containing HMG-1. The maximum inhibition observed was 55% and taking into account that only 65% of the substrates had HMG-1 bound, approximately 85% inhibition was observed on platinated DNA substrates containing HMG-1. Inhibition of helicase activity was proportional to the amount of substrate bound by HMG-1 based on the displacement and exonuclease assays at varying HMG-1 concentrations. The ability of helicase E to displace an undamaged DNA oligonucleotide from a cisplatin-damaged DNA template was also inhibited by HMG-1. Interestingly, HMG-1 had no effect on the rate of DNA-dependent ATP hydrolysis catalyzed by helicase E on the same DNA substrate. The inhibition of helicase activity by HMG-1 binding cisplatin-damaged DNA further supports a role for HMG-1 inhibiting DNA repair which may contribute to cellular sensitivity to cisplatin.