P53 mediates estradiol induced activation of apoptosis and DNA repair in non-malignant colonocytes

Implications of estrogen and its receptors in colorectal carcinoma

Estrogens have been implicated in the pathogenesis of various cancer types, including colorectal carcinoma (CRC). Estrogen receptors such as ERα and ERβ activate intracellular signaling cascades followed by binding to estrogen, resulting in important changes in cellular behaviors. The nuclear estrogen receptors, i.e. ERβ and ERα are responsible for the genomic actions of estrogens, whereas the other receptor, such as G protein-coupled estrogen receptor (GPER) regulates rapid non-genomic actions, which lead to secondary gene expression changes in cells. ERβ, the predominant estrogen receptor expressed in both normal and non-malignant colonic epithelium, has protective roles in colon carcinogenesis. ERβ may exert the anti-tumor effect through selective activation of pro-apoptotic signaling, increasing DNA repair, inhibiting expression of oncogenes, regulating cell cycle progression, and also by changing the micro-RNA pool and DNA-methylation. Thus, a better understanding of the underlying mechanisms of estrogen and its receptors in CRC pathogenesis could provide a new horizon for effective therapeutic development. Furthermore, using synthetic or natural compounds as ER agonists may induce estrogen-mediated anti-cancer activities against colon cancer. In this study, we report the most recent pre-clinical and experimental evidences related to ERs in CRC development. Also, we reviewed the actions of naturally occurring and synthetic compounds, which have a protective role against CRC development by acting as ER agonist.

Estrogen receptor actions in colitis

In recent years, researchers have demonstrated that estrogen and its receptors, aside from their role in regulating several biological functions, contribute to the development and progression/severity of inflammatory bowel diseases (IBDs). IBDs include both ulcerative colitis (UC) and Crohn's disease (CD). Epidemiological data indicate a clear difference in the incidence, severity, and complications of IBDs between sexes. Men present a higher risk of developing colitis than women and a higher risk of developing colorectal cancer, a common complication of this condition. However, fluctuations of estrogen levels have yielded inconsistent data, where oral contraceptives and hormone replacement therapy have been associated with an increased risk of IBDs in premenopausal women but significantly reduce disease activity after menopause. Likewise, improvement of symptoms related to CD has been reported during pregnancy, but not in UC, who often experience worsening symptoms. In the colonic epithelium, estrogen receptor β (ERβ) is the predominant form of the protein expressed, and it helps maintain normal epithelial function and organization. Preclinical data suggest that ER expression and activation via estrogen confers different responses on disease severity depending on the model used to induce colitis, which may reflect what is observed in patients with IBDs. Hence, this review aims to provide an overview of estrogen and its receptors, particularly ERβ, in the pathophysiology of IBDs.

Role of Sex in the Therapeutic Targeting of p53 Circuitry

Sex profoundly affects cancer incidence and susceptibility to therapy, with sex hormones highly contributing to this disparity. Various studies and omics data suggest a relationship between sex and the oncosuppressor p53 circuitry, including its regulators MDM2 and MDM4. Association of this network with genetic variation underlies sex-related altered cancer risk, age of onset, and cancer sensitivity to therapy. Moreover, sex-related factors, mainly estrogenic hormones, can affect the levels and/or function of the p53 network both in hormone-dependent and independent cancer. Despite this evidence, preclinical and clinical studies aimed to evaluate p53 targeted therapy rarely consider sex and related factors. This review summarizes the studies reporting the relationship between sex and the p53 circuitry, including its associated regulators, MDM2 and MDM4, with particular emphasis on estrogenic hormones. Moreover, we reviewed the evaluation of sex/hormone in preclinical studies and clinical trials employing p53-target therapies, and discuss how patients’ sex and hormonal status could impact these therapeutic approaches.

Effects of high-fat diet and intestinal aryl hydrocarbon receptor deletion on colon carcinogenesis

Consumption of a high-fat diet has been associated with an increased risk of developing colorectal cancer (CRC). However, the effects of the interaction between dietary fat content and the aryl hydrocarbon receptor (AhR) on colorectal carcinogenesis remain unclear. Mainly known for its role in xenobiotic metabolism, AhR has been identified as an important regulator for maintaining intestinal epithelial homeostasis. Although previous research using whole body AhR knockout mice has revealed an increased incidence of colon and cecal tumors, the unique role of AhR activity in intestinal epithelial cells (IECs) and modifying effects of fat content in the diet at different stages of sporadic CRC development are yet to be elucidated. In the present study, we have examined the effects of a high-fat diet on IEC-specific AhR knockout mice in a model of sporadic CRC. Although loss of AhR activity in IECs significantly induced the development of premalignant lesions, in a separate experiment, no significant changes in colon mass incidence were observed. Moreover, consumption of a high-fat diet promoted cell proliferation in crypts at the premalignant colon cancer lesion stage and colon mass multiplicity as well as β-catenin expression and nuclear localization in actively proliferating cells in colon masses. Our data demonstrate the modifying effects of high-fat diet and AhR deletion in IECs on tumor initiation and progression.NEW & NOTEWORTHY Through the use of an intestinal-specific aryl hydrocarbon receptor (AhR) knockout mouse model, this study demonstrates that the expression of AhR in intestinal epithelial cells is required to reduce the formation of premalignant colon cancer lesions. Furthermore, consumption of a high-fat diet and the loss of AhR in intestinal epithelial cells influences the development of colorectal cancer at various stages.

Effects of Estrogen on the Gastrointestinal Tract

Estrogen is a kind of steroid compound that has extensive biologic activities. The effect of estrogen is pleiotropic, affecting multiple systems in the body. There is accumulating evidence that estrogen has important effects on the gastrointestinal tract. Longer exposure to estrogen may decrease the risk of gastric cancer. Use of the anti-estrogen drug tamoxifen might increase the risk of gastric adenocarcinoma. Estrogen receptor β may serve as a target for colorectal cancer prevention. In addition, estrogen has been reported to be closely related to the mucosal barrier, gastrointestinal function and intestinal inflammation. However, the role of estrogen in the gastrointestinal tract has not been systematically summarized. In this review, we aim to provide an overview of the role of estrogen in the gastrointestinal tract and evaluate it from various aspects, including estrogen receptors, the mucosal barrier, intestinal inflammation and gastrointestinal tract tumors, which may provide the basis for the development of therapeutic strategies to manage gastrointestinal diseases.

Mismatch Repair Protein hMLH1, but not hMSH2, Enhances Estrogen-Induced Apoptosis of Colon Cancer Cells

BACKGROUND

Epidemiological studies suggest a protective role of estrogen against colon carcinogenesis; this effect appears to be dependent on mismatch repair (MMR) status. However, the underlying mechanism remains unclear. This study investigated the role of MMR proteins in apoptosis of colon cancer cells in the presence or absence of estrogen.

METHODS

Two major MMR proteins, human mutL homolog 1 (hMLH1) and mutS homolog 2 (hMSH2), as well as estrogen receptor-β (ERβ), were transiently expressed in either hMLH1-deficient HCT116 cells or hMSH2-deficient LoVo cells. Effects of estradiol on cell viability and apoptosis were assessed. Furthermore, we examined the apoptotic status of epithelial cells in colonic mucosa taken from previous healthy female subjects with menopausal syndrome before and after 6-month hormone replacement therapy (HRT).

RESULTS

In hMLH1-deficient HCT116 cells, re-expression of hMLH1 led to a significantly decreased cell viability and increased apoptosis, which were further enhanced by estradiol, including marked increase of activated caspase-3 and caspase-9, as well as Bax and P53. The effect of hMLH1 overexpression in LoVo cells resulted in a similar increase in apoptosis that was greatly stimulated by estradiol. The enhanced apoptosis by hMLH1 and estradiol was further validated by FACS analyses of Annexin V expression. Re-expression of hMSH2 or overexpression of ERβ in HCT116 cells also enhanced apoptosis; however, the effects were independent of estradiol. Furthermore, studies on healthy menopausal women before and after 6-month HRT demonstrated a significant HRT-mediated upregulation of the hMLH1 expression, with concomitant elevation of caspase-3 and caspase-9 activation in the colonic mucosa.

CONCLUSION

We present the first evidence that hMLH1 and hMSH2 have similar but distinct roles in the apoptosis of colon cancer cells: an increased expression of either one can promote apoptosis, while only the effect of hMLH1 but not hMSH2 is estradiol-dependent. Our data suggest that MMR status should be assessed before hormone replacement therapy or future application of estrogen-based chemoprevention.

Estrogen receptor beta as target for colorectal cancer prevention

Colorectal cancer (CRC) is a leading cause of death in the United States. Despite its slow development and the capacity for early diagnosis, current preventive approaches are not sufficient. However, a role for estrogen has been demonstrated in multiple epidemiologic studies, which may benefit CRC prevention. A large body of evidence from preclinical studies indicates that expression of the estrogen receptor beta (ERβ/ESR2) demonstrates an inverse relationship with the presence of colorectal polyps and stage of tumors, and can mediate a protective response. Natural compounds, including phytoestrogens, or synthetic ERβ selective agonists, can activate or upregulate ERβ in the colon and promote apoptosis in preclinical models and in clinical experience. Importantly, this activity has been associated with a reduction in polyp formation and, in rodent models of CRC, has been shown to lower incidence of colon adenocarcinoma. Collectively, these findings indicate that targeted activation of ERβ may represent a novel clinical approach for management of colorectal adenomatous polyps and prevention of colorectal carcinoma in patients at risk for this condition. In this review, we discuss the potential of new chemopreventive or dietary approaches based on estrogen signaling.

Persistent Simian Immunodeficiency Virus Infection Causes Ultimate Depletion of Follicular Th Cells in AIDS

CD4(+) T follicular helper (Tfh) cells are critical for the generation of humoral immune responses to pathogenic infections, providing help for B cell development, survival, and affinity maturation of Abs. Although CD4(+) Tfh cells are reported to accumulate in HIV or SIV infection, we found that germinal center Tfh cells, defined in this study as CXCR5(+)PD-1(HIGH)CD4(+) T cells, did not consistently accumulate in chronically SIV-infected rhesus macaques compared with those infected with less pathogenic simian HIV, vaccinated and SIVmac-challenged, or SIVmac-infected Mamu-A*01(+) macaques, all of which are associated with some control of virus replication and slower disease progression. Interestingly, CXCR5(+)PD-1(HIGH) Tfh cells in lymphoid tissues were eventually depleted in macaques with AIDS compared with the other cohorts. Chronic activation and proliferation of CXCR5(+)PD-1(HIGH) Tfh were increased, but PD-L2 expression was downregulated on B cells, possibly resulting in germinal center Tfh cell apoptosis. Together, these findings suggest that changes in CXCR5(+)PD-1(HIGH) Tfh cells in lymph nodes correlate with immune control during infection, and their loss or dysregulation contribute to impairment of B cell responses and progression to AIDS.

Enhanced action of apigenin and naringenin combination on estrogen receptor activation in non-malignant colonocytes: implications on sorghum-derived phytoestrogens

We report unusually strong enhanced effect of apigenin-naringenin combination and natural flavonoid mixtures on estrogenic response in non-malignant young adult mouse colonocytesin vitro.

The p53-estrogen receptor loop in cancer

Tumor suppressor p53 maintains genome stability by regulating diverse cellular functions including cell cycle arrest, apoptosis, senescence and metabolic homeostasis. Mutations in the p53 gene occur in almost all human cancers with a frequency of up to 80%. However, it is only 20% in breast cancers, 18% in endometrial cancers and 1.5% in cervical cancers. Estrogen receptor alpha (ERα) plays a pivotal role in hormone-dependent cancer development and the status of ERα is used for designing treatment strategy and for prognosis. A closer look at the cross-talk between p53 and ERα has revealed that their activities are mutually regulated. This review will summarize the current body of knowledge on p53, ERα and ERβ in cancer. Clinical correlations between estrogen receptors and p53 status have also been reported. Thus, this review will discuss the relationship between p53 and ERs at both the molecular and clinical levels.

Association between genetic polymorphisms in apoptosis-related genes and risk of cutaneous melanoma in women and men

BACKGROUND

The P53 Arg72Pro, MDM2 c.+309T>G, BAX c.-248G>A, and BCL2 c.-717C>A polymorphisms have variable roles in the apoptosis pathways.

OBJECTIVE

To clarify the roles of these polymorphisms in the risk for cutaneous melanoma (CM).

METHODS

Genomic DNA of 200 CM patients and 215 controls was analyzed by PCR-RFLP.

RESULTS

In women, the frequencies of BAX GG (83.0% vs. 71.0%, P=0.04), BCL2 AA (32.0% vs. 15.0%, P=0.003), P53 ArgArg plus BAX GG (84.9% vs. 63.2%, P=0.01), P53 ArgArg plus BCL2 AA (37.0% vs. 13.1%, P=0.003), BAX GG plus BCL2 AA (70.3% vs. 33.3%, P=0.001), MDM2 GG plus BAX GG plus BCL2 AA (27.3% vs. 3.7%, P=0.03), and P53 ArgArg plus MDM2 GG plus BAX GG plus BCL2 AA (33.3% vs. 5.6%, P=0.04) genotypes were higher in patients than in controls. Female carriers of the respective genotypes were under 1.98 (95% CI: 1.01-3.91), 2.87 (95% CI: 1.43-5.77), 3.48 (95% CI: 1.34-9.04), 4.23 (95% CI: 1.63-10.96), 6.04 (95% CI: 2.10-17.37), 25.61 (95% CI: 1.29-507.24), and 25.69 (95% CI: 1.11-593.59)-fold increased risks for CM than others, respectively. In men, the frequencies of BCL2 CA+AA (83.0% vs. 67.6%, P=0.01) and MDM2 TG+GG plus BCL2 CA+AA (94.2% vs. 68.3%, P=0.003) genotypes were higher in patients than in controls. Male carriers of the respective genotypes were under 2.43 (95% CI: 1.23-4.82) and 9.22 (95% CI: 2.16-39.31)-fold increased CM risks than others, respectively.

CONCLUSION

The data suggest for the first time that P53 Arg72Pro, MDM2 c.+309T>G, BAX c.-248G>A, and BCL2 c.-717C>A polymorphisms, enrolled in apoptosis pathways, constitute distinct determinants of CM in women and men.

A novel shift in estrogen receptor expression occurs as estradiol suppresses inflammation-associated colon tumor formation

Postmenopausal women on estrogen replacement therapy (ERT) have a reduced risk of developing colon cancer compared with postmenopausal women not on ERT, suggesting a role for estradiol (E2) in protection against this disease. To determine whether E2 protects against inflammation-associated colon cancer when administered following the initiation of colonic DNA damage, in this study, we implanted E2-containing pellets into mice after co-treatment with azoxymethane and two rounds of dextran sulfate sodium (DSS). Wild-type (WT) E2-treated mice had reduced numbers and average area of adenocarcinomas compared with the control mice. These effects were lost in estrogen receptor-β (Erβ (Esr2)) knockout mice. Surprisingly, apoptosis was reduced and cell proliferation was increased in sections from tumors of the WT E2 mice compared with the WT control mice. These findings are probably due, in part, to a reduction in ERβ expression in colonic epithelial cells as the cells progressed from a non-malignant to a cancerous state as enhanced apoptosis was observed in normal colonocytes expressing higher levels of ERβ. Furthermore, epithelial cells within the tumors had dramatically increased ERα mRNA and protein expression compared with the non-diseased mice. We conclude that while E2 treatment resulted in an overall suppression of colonic adenocarcinoma formation, reduced ERβ expression accompanied by enhanced ERα expression caused an altered colonocyte response to E2 treatment compared with the earlier stages of colon cancer development. These data are the first examples of decreased ERβ expression concurrent with increased ERα expression as a disease develops and highlight the importance of understanding the timing of E2 exposure with regard to the prevention of inflammation-associated colon cancer.

Estrogen receptor β expression induces changes in the microRNA pool in human colon cancer cells

There is epidemiological, animal and in vitro evidence that estrogen receptor β (ERβ) can mediate protective effects against colon cancer, but the mechanism is not completely understood. Previous research has indicated critical pathways whereby ERβ acts in an antitumorigenic fashion. In this study, we investigate ERβ's impact on the microRNA (miRNA) pool in colon cancer cells using large-scale genomic approaches, bioinformatics and focused functional studies. We detect and confirm 27 miRNAs to be significantly changed following ERβ expression in SW480 colon cancer cells. Among these, the oncogenic miR-17-92 cluster and miR-200a/b are strongly downregulated. Using target prediction and anticorrelation to gene expression data followed by focused mechanistic studies, we demonstrate that repression of miR-17 is a secondary event following ERβ's downregulatory effect on MYC. We show that re-introduction of miR-17 can reverse the antiproliferative effects of ERβ. The repression of miR-17 also influences cell death upon DNA damage and mediates regulation of NCOA3 (SRC-3) and CLU in colon cancer cells. We further determine that the downregulation of miR-200a/b mediates increased ZEB1 while decreasing E-cadherin levels in ERβ-expressing colon cancer cells. Changes in these genes correspond to significant alterations in morphology and migration. Our work contributes novel data of ERβ and miRNA in the colon. Elucidating the mechanism of ERβ and biomarkers of its activity has significant potential to impact colon cancer prevention and treatment.