HTLV-1 Tax oncoprotein inhibits the estrogen-induced-ER α-Mediated BRCA1 expression by interaction with CBP/p300 cofactors

The Interplay between the Cellular Response to DNA Double-Strand Breaks and Estrogen

Cancer development is often connected to impaired DNA repair and DNA damage signaling pathways. The presence of DNA damage in cells activates DNA damage response, which is a complex cellular signaling network that includes DNA repair, activation of the cell cycle checkpoints, cellular senescence, and apoptosis. DNA double-strand breaks (DSBs) are toxic lesions that are mainly repaired by the non-homologous end joining and homologous recombination repair (HRR) pathways. Estrogen-dependent cancers, like breast and ovarian cancers, are frequently associated with mutations in genes that play a role in HRR. The female sex hormone estrogen binds and activates the estrogen receptors (ERs), ERα, ERβ and G-protein-coupled ER 1 (GPER1). ERα drives proliferation, while ERβ inhibits cell growth. Estrogen regulates the transcription, stability and activity of numerus DDR factors and DDR factors in turn modulate ERα expression, stability and transcriptional activity. Additionally, estrogen stimulates DSB formation in cells as part of its metabolism and proliferative effect. In this review, we will present an overview on the crosstalk between estrogen and the cellular response to DSBs. We will discuss how estrogen regulates DSB signaling and repair, and how DDR factors modulate the expression, stability and activity of estrogen. We will also discuss how the regulation of HRR genes by estrogen promotes the development of estrogen-dependent cancers.

Predicted Cellular Interactors of the Endogenous Retrovirus-K Integrase Enzyme

Integrase (IN) enzymes are found in all retroviruses and are crucial in the retroviral integration process. Many studies have revealed how exogenous IN enzymes, such as the human immunodeficiency virus (HIV) IN, contribute to altered cellular function. However, the same consideration has not been given to viral IN originating from symbionts within our own DNA. Endogenous retrovirus-K (ERVK) is pathologically associated with neurological and inflammatory diseases along with several cancers. The ERVK IN interactome is unknown, and the question of how conserved the ERVK IN protein-protein interaction motifs are as compared to other retroviral integrases is addressed in this paper. The ERVK IN protein sequence was analyzed using the Eukaryotic Linear Motif (ELM) database, and the results are compared to ELMs of other betaretroviral INs and similar eukaryotic INs. A list of putative ERVK IN cellular protein interactors was curated from the ELM list and submitted for STRING analysis to generate an ERVK IN interactome. KEGG analysis was used to identify key pathways potentially influenced by ERVK IN. It was determined that the ERVK IN potentially interacts with cellular proteins involved in the DNA damage response (DDR), cell cycle, immunity, inflammation, cell signaling, selective autophagy, and intracellular trafficking. The most prominent pathway identified was viral carcinogenesis, in addition to select cancers, neurological diseases, and diabetic complications. This potentiates the role of ERVK IN in these pathologies via protein-protein interactions facilitating alterations in key disease pathways.

Viral Manipulation of the Host Epigenome as a Driver of Virus-Induced Oncogenesis

Tumorigenesis due to viral infection accounts for a high fraction of the total global cancer burden (15–20%) of all human cancers. A comprehensive understanding of the mechanisms by which viral infection leads to tumor development is extremely important. One of the main mechanisms by which viruses induce host cell proliferation programs is through controlling the host’s epigenetic machinery. In this review, we dissect the epigenetic pathways through which oncogenic viruses can integrate their genome into host cell chromosomes and lead to tumor progression. In addition, we highlight the potential use of drugs based on histone modifiers in reducing the global impact of cancer development due to viral infection.

BRCA1 represses DNA replication initiation through antagonizing estrogen signaling and maintains genome stability in parallel with WEE1-MCM2 signaling during pregnancy

The mammary gland undergoes fast cell proliferation during early pregnancy, yet the mechanism to ensure genome integrity during this highly proliferative stage is largely unknown. We show that pregnancy triggers replicative stresses leading to genetic instability in mice carrying a mammary specific disruption of breast cancer associated gene-1 (BRCA1). The fast cell proliferation was correlated with enhanced expression of most genes encoding replisomes, which are positively regulated by estrogen/ERα signaling but negatively regulated by BRCA1. Our further analysis revealed two parallel signaling pathways, which are mediated by ATR-CHK1 and WEE1-MCM2 and are responsible for regulating DNA replication checkpoint. Upon DNA damage, BRCA1 deficiency markedly enhances DNA replication initiation and preferably impairs DNA replication checkpoint mediated by ATR and CHK1. Meanwhile, DNA damage also activates WEE1-MCM2 signaling, which inhibits DNA replication initiation and enables BRCA1-deficient cells to avoid further genomic instability. Finally, we demonstrated that overriding this defense by WEE1 inhibition in combination with cisplatin, which causes DNA damage, serves as a promising therapeutic approach for killing BRCA1-deficient cancer cells.

Role of p300 in the pathogenesis of Henoch-Schonlein purpura nephritis and as a new target of glucocorticoid therapy in mice

Background:

Henoch-Schonlein purpura nephritis (HSPN) is a very common secondary kidney disease of childhood. Its pathogenesis and the treatment mechanism of glucocorticoid have not been fully elucidated. The aim of this study was to determine the relationship between p300 and the pathogenesis, glucocorticoid therapy in mice with HSPN, respectively.

Methods:

Forty-eight C57BL/6N male mice, weighing 18 to 20 g, were selected (3–4 weeks old, n = 8 per group). The mice in the normal control group (Group I) were given normal solvent and the HSPN model group (Group II) were given sensitizing drugs. The mice in Group III were injected intraperitoneally with dexamethasone after being given sensitizing drugs. Meanwhile, mice in Groups IV, V and VI with conditional knockout of p300 were also given normal solvent, sensitizing drugs and dexamethasone.

The levels of serum IgA, creatinine, and circulating immune complex (CIC) concentrations, 24 h urinary protein and urinary erythrocyte in C57 wild mice, and p300 conditional knockout mice in each group were measured. The expression of p300 in renal tissues and the expression of glucocorticoid receptor (GR) α and β, transforming growth factor (TGF)-β1, and activator protein (AP)-1 after dexamethasone treatment were determined by real-time polymerase chain reaction and Western blotting.

Results:

Compared with the normal solvent control group (Group I), the expression of p300 mRNA in the model group (Group II) was significantly up-regulated. Western blotting further confirmed the result. Urinary erythrocyte count, 24 h urinary protein quantification, serum IgA, CIC, and renal pathologic score in Group V were distinctly decreased compared with non-knockout mice in Group II (9.7 ± 3.8 per high-power field [/HP] vs. 18.7 ± 6.2/HP, t = 1.828, P = 0.043; 0.18 ± 0.06 g/24 h vs. 0.36 ± 0.08 g/24 h, t = 1.837, P = 0.042; 18.78 ± 0.85 mg/mL vs. 38.46 ± 0.46 mg/mL, t = 1.925, P = 0.038; 0.80 ± 0.27 μg/mL vs. 1.64 ± 0.47 μg/mL, t = 1.892, P = 0.041; 7.0 ± 0.5 vs. 18.0 ± 0.5, t = 1.908, P = 0.039). Compared with non-knockout mice (Group III), the level of urinary erythrocyte count and serum IgA in knockout mice (Group VI) increased significantly after treatment with dexamethasone (3.7 ± 0.6/HP vs. 9.2 ± 3.5/HP, t = 2.186, P = 0.024; 12.38 ± 0.26 mg/mL vs. 27.85 ± 0.65 mg/mL, t = 1.852, P = 0.041). The expression level of GRα was considerably increased in the knockout group after dexamethasone treatment compared with non-knockout mice in mRNA and protein level (t = 2.085, P = 0.026; t = 1.928, P = 0.035), but there was no statistically significant difference in the expression level of GRβ between condition knockout and non-knockout mice (t = 0.059, P = 0.087; t = 0.038, P = 1.12). Furthermore, the expression levels of glucocorticoid resistance genes (AP-1 and TGF-β1) were notably increased after p300 knockout compared with non-knockout mice in mRNA and protein level (TGF-β1: t = 1.945, P = 0.034; t = 1.902, P = 0.039; AP-1: t = 1.914, P = 0.038; t = 1.802, P = 0.041).

Conclusions:

p300 plays a crucial role in the pathogenesis of HSPN. p300 can down-regulate the expression of resistance genes (AP-1 and TGF-β1) by binding with GRα to prevent further renal injury and glucocorticoid resistance. Therefore, p300 is a promising new target in glucocorticoid therapy in HSPN.

Clinical Features of Breast Cancer Patients with Human T-Cell Lymphotropic Virus Type-1 Infection

Background: Human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus that causes adult T-cell leukemia/lymphoma (ATL), an aggressive form of T-cell malignancy. The relationship between HTLV-1 infection and cancer progression is controversial. HTLV-1 encodes oncogenic protein TAX1 and it is hypothesized that HTLV-1 infection is associated with breast cancer progression. In this study, we evaluated the relationship between HTLV-1 infection and clinicopathological factors in breast cancer patients. Methods: We retrospectively analyzed 610 patients with primary breast cancer who underwent surgical treatment without preoperative chemotherapy at Kagoshima University Hospital between January 2001 and January 2015. Results: When patients with and without HTLV-1 infection were compared, no differences in clinicopathological factors were observed, except for age. Disease-free survival and overall survival rates did not differ between groups. Conclusions: HTLV-1–positive patients were significantly older than HTLV-1–negative patients. It was supposed to be due to the fact that the HTLV-1 infection rate is decreasing. Any effect of HTLV-1 infection on breast cancer progression appears to be negligibly small.

Effect of TPA and HTLV-1 Tax on BRCA1 and ERE controlled genes expression

Interference with the expression and/or functions of the multifunctional tumor suppressor BRCA1 leads to a high risk of breast and ovarian cancers. BRCA1 expression is usually activated by the estrogen (E2) liganded ERα receptor. Activated ERα is considered as a potent transcription factor which activates various genes expression by 2 pathways. A classical pathway, ERα binds directly to E2-responsive elements (EREs) in the promoters of the responsive genes and a non-classical pathway where ERα indirectly binds with the appropriate gene promoter. In our previous study, HTLV-1Tax was found to strongly inhibit ERα induced BRCA1 expression while stimulating ERα induced ERE dependent genes. TPA is a strong PKC activator which found to induce the expression of HTLV-1. Here we examined the effect of TPA on the expression of BRCA1 and genes controlled by ERE region in MCF-7 cells and on Tax activity on these genes. Our results showed strong stimulatory effect of TPA on both BRCA1 and ERE expression without treatment with E2. Tax did not show any significant effect on these TPA activities. It seems that TPA activation of BRCA1 and ERE expression is dependent on PKC activity but not through the NFκB pathway. However, 53BP1 may be involved in this TPA activity because its overexpression significantly reduced the TPA stimulatory effect on BRCA1 and ERE expression. Additionally, our Chip assay results probably exclude possible involvement of ERα pathway in this TPA activity because TPA did not interfere with the binding of ERα to both BRCA1 promoter and ERE region.

Differential effects of HTLV-1 Tax oncoprotein on the different estrogen-induced-ER α-mediated transcriptional activities

The activated estrogen (E2) receptor α (ERα) is a potent transcription factor that is involved in the activation of various genes by 2 different pathways; a classical and non-classical. In classical pathway, ERα binds directly to E2-responsive elements (EREs) located in the appropriate genes promoters and stimulates their transcription. However, in non-classical pathway, the ERα can indirectly bind with promoters and enhance their activity. For instance, ERα activates BRCA1 expression by interacting with jun/fos complex bound to the AP-1 site in BRCA1 promoter. Interference with the expression and/or functions of BRCA1, leads to high risk of breast or/and ovarian cancer. HTLV-1Tax was found to strongly inhibit BRCA1 expression by preventing the binding of E2-ERα complex to BRCA1 promoter. Here we examined Tax effect on ERα induced activation of genes by the classical pathway by testing its influence on E2-induced expression of ERE promoter-driven luciferase reporter (ERE-Luc). Our findings showed that E2 profoundly stimulated this reporter expression and that HTLV-1Tax significantly induced this stimulation. This result is highly interesting because in our previous study Tax was found to strongly block the E2-ERα-mediated activation of BRCA1 expression. ERα was found to produce a big complex by recruiting various cofactors in the nucleus before binding to the ERE region. We also found that only part of the reqruited cofactors are required for the transcriptional activity of ERα complex. Chip assay revealed that the binding of Tax to the ERα complex, did not interfere with its link to ERE region.

Epigenetic Pathways of Oncogenic Viruses: Therapeutic Promises

Cancerous transformation comprises different events that are both genetic and epigenetic. The ultimate goal for such events is to maintain cell survival and proliferation. This transformation occurs as a consequence of different features such as environmental and genetic factors, as well as some types of infection. Many viral infections are considered to be causative agents of a number of different malignancies. To convert normal cells into cancerous cells, oncogenic viruses must function at the epigenetic level to communicate with their host cells. Oncogenic viruses encode certain epigenetic factors that lead to the immortality and proliferation of infected cells. The epigenetic effectors produced by oncogenic viruses constitute appealing targets to prevent and treat malignant diseases caused by these viruses. In this review, we highlight the importance of epigenetic reprogramming for virus-induced oncogenesis, with special emphasis on viral epigenetic oncoproteins as therapeutic targets. The discovery of molecular components that target epigenetic pathways, especially viral factors, is also discussed.

HTLV-I Tax-Mediated Inactivation of Cell Cycle Checkpoints and DNA Repair Pathways Contribute to Cellular Transformation: "A Random Mutagenesis Model"

To achieve cellular transformation, most oncogenic retroviruses use transduction by proto-oncogene capture or insertional mutagenesis, whereby provirus integration disrupts expression of tumor suppressors or proto-oncogenes. In contrast, the Human T-cell leukemia virus type 1 (HTLV-I) has been classified in a separate class referred to as "transactivating retroviruses". Current views suggest that the viral encoded Tax protein transactivates expression of cellular genes leading to deregulated growth and transformation. However, if Tax-mediated transactivation was indeed sufficient for cellular transformation, a fairly high frequency of infected cells would eventually become transformed. In contrast, the frequency of transformation by HTLV-I is very low, likely less than 5%. This review will discuss the current understanding and recent discoveries highlighting critical functions of Tax in cellular transformation. HTLV-I Tax carries out essential functions in order to override cell cycle checkpoints and deregulate cellular division. In addition, Tax expression is associated with increased DNA damage and genome instability. Since Tax can inhibit multiple DNA repair pathways and stimulate unfaithful DNA repair or bypass checkpoints, these processes allow accumulation of genetic mutations in the host genome. Given this, a "Random Mutagenesis" transformation model seems more suitable to characterize the oncogenic activities of HTLV-I.