Faculty Bibliography

Invasive bladder cancer (BC) is one of the most lethal malignant urological tumors. Although miR-200a has been reported as an onco-miRNA that targets the PTEN gene in endometrioid carcinoma, its biological significance in BC invasion has been poorly explored. In the current study, we found that miR-200a was markedly overexpressed in both human BC tissues and BBN-induced muscle-invasive BC tissues. We further showed that miR-200a overexpression specifically promoted human BC cell invasion, but not migration, via transcriptional upregulation of matrix metalloproteinase (MMP)-2. Mechanistic studies indicated that the increased phosphorylation of c-Jun mediated the increasing levels of MMP-2 mRNA transcription. Further investigation revealed that Dicer was decreased in miR-200a overexpressed BC cells; this resulted in inhibition of miR-16 maturation and consequently led to increased JNK2 protein translation and c-Jun activation. Taken together, the studies here showed that miR-200a overexpression inhibited Dicer expression, in turn, resulted in inhibition of miR-16 maturation, leading to upregulation of JNK2 expression, c-Jun phosphorylation, MMP-2 transcription and, ultimately, BC invasion. Collectively, these results demonstrate that miR-200a is an onco-miRNA that is a positive regulator for BC invasion. This finding could be very useful in the ongoing development of new strategies to treat invasive BC patients.

Arsenic, a class I human carcinogen, is ubiquitously found throughout the environment and around the globe, posing a great public health concern. Notably, Bangladesh and regions of West Bengal have been found to have high levels (0.5-4600 μg/L) of arsenic drinking water contamination, and approximately 50 million of the world's 200 million people chronically exposed to arsenic in Bangladesh alone. This study was carried out to examine genome-wide gene expression changes in individuals chronically exposed to arsenic-contaminated drinking water. Our study population includes twenty-nine Bangladeshi female participants with urinary arsenic levels ranging from 22.32 to 1828.12 μg/g creatinine. RNA extracted from peripheral blood mononuclear cells (PBMCs) were evaluated using RNA-Sequencing analysis. Our results indicate that a total of 1,054 genes were significantly associated with increasing urinary arsenic levels (FDR p < 0.05), which include 418 down-regulated and 636 up-regulated genes. Further Ingenuity Pathway Analysis revealed potential target genes (DAPK1, EGR2, APP), microRNAs (miR-155, -338, -210) and pathways (NOTCH signaling pathway) related to arsenic carcinogenesis. The selection of female-only participants provides a homogenous study population since arsenic has significant sex dependent effects, and the wide exposure range provides new insight for key gene expression changes that correlate with increasing urinary arsenic levels.

Chromium (Cr) is a naturally occurring metallic element found in the Earth's crust. While trivalent chromium ([Cr(III)] is considered non-carcinogenic, hexavalent chromium [Cr(VI)] has long been established as an IARC class I human carcinogen, known to induce cancers of the lung. Current literature suggests that Cr(VI) is capable of inducing carcinogenesis through both genetic and epigenetic mechanisms. Although much has been learned about the molecular etiology of Cr(VI)-induced lung carcinogenesis, more remains to be explored. In particular, the explicit epigenetic alterations induced by Cr(VI) in lung cancer including histone modifications and miRNAs, remain understudied. Through comprehensive review of available literature found between 1973 and 2019, this article provides a summary of updated understanding of the molecular mechanisms of Cr(VI)-carcinogenesis. In addition, this review identifies potential research gaps in the areas of histone modifications and miRNAs, which may prompt new niches for future research.

Arsenic is a naturally occurring and highly potent metalloid known to elicit serious public health concerns. Today, approximately 200 million people around the globe are exposed to arsenic-contaminated drinking water at levels greater than the World Health Organization's recommended limit of 10 parts per billion. As a class I human carcinogen, arsenic exposure is known to elicit various cancers, including lung, skin, liver, and kidney. Current evidence suggests that arsenic is capable of inducing both genotoxic and cytotoxic injury, as well as activating epigenetic pathways to induce carcinogenesis. Our study identifies a novel pathway that is implicated in arsenic-induced carcinogenesis. Arsenic down-regulated miRNA-31 and the release of this inhibition caused overexpression of special AT-rich sequence-binding protein 2 (SATB2). Arsenic is known to disrupt miRNA expression, and here we report for the first time that arsenic is capable of inhibiting miR-31 expression. As a direct downstream target of miR-31, SATB2 is a prominent transcription factor and nuclear matrix binding protein implicated in many types of human diseases including lung cancer. Results from this study show that arsenic induces the overexpressing SATB2 by inhibiting miR-31 expression, which blocks the translation of SATB2 mRNA, since levels of SATB2 mRNA remain the same but protein levels decrease. Overexpression of SATB2 induces malignant transformation of human bronchial epithelial (BEAS-2B) cells indicating the importance of the expression of miR-31 in preventing carcinogenesis by suppressing SATB2 protein levels.

Ultraviolet radiation (UVR) from sunlight is the major effector for skin aging and carcinogenesis. However, genes and pathways altered by solar-simulated UVR (ssUVR), a mixture of UVA and UVB, are not well characterized. Here we report global changes in gene expression as well as associated pathways and upstream transcription factors in human keratinocytes exposed to ssUVR. Human HaCaT keratinocytes were exposed to either a single dose or 5 repetitive doses of ssUVR. Comprehensive analyses of gene expression profiles as well as functional annotation were performed at 24 hours post irradiation. Our results revealed that ssUVR modulated genes with diverse cellular functions changed in a dose-dependent manner. Gene expression in cells exposed to a single dose of ssUVR differed significantly from those that underwent repetitive exposures. While single ssUVR caused a significant inhibition in genes involved in cell cycle progression, especially G2/M checkpoint and mitotic regulation, repetitive ssUVR led to extensive changes in genes related to cell signaling and metabolism. We have also identified a panel of ssUVR target genes that exhibited persistent changes in gene expression even at 1 week after irradiation. These results revealed a complex network of transcriptional regulators and pathways that orchestrate the cellular response to ssUVR.

Both nickel and cadmium compounds have been established as group I carcinogens for several decades. Despite over-whelming evidence of these compounds' carcinogenicity in humans, the specific underlying molecular mechanisms that govern metal induced cellular transformation remain unclear. In this study, we found that there were slightly different effects on decreased SLBP mRNA and protein as well as increased polyA H3.1 in our nickel exposed cells. This suggested that nickel and arsenic have similar effects on canonical histone mRNA transcription and translation. We also saw that the depletion of SLBP protein was reversed by inhibiting the proteosome. Finally, we showed that inhibiting the SLBP mRNA and protein levels were rescued by epigenetic modifiers suggesting that nickel's effects on SLBP may be mediated via epigenetic mechanisms. Taken together these results suggest a similar mechanism by which both arsenic and nickel may exert their carcinogenic effects.

In the course of our investigations into the toxicity of tungstate, we discovered that cellular exposure resulted in the loss of the histone demethylase protein. We specifically investigated the loss of two histone demethylase dioxygenases, JARID1A and JMJD1A. Both of these proteins were degraded in the presence of tungstate and this resulted in increased global levels of H3K4me3 and H3K9me2, the substrates of JARID1A and JMJD1A respectively. Treatment with MG132 completely inhibited the loss of the demethylase proteins induced by tungstate treatment, suggesting that tungstate activated the proteasomal degradation of these proteins. The changes in global histone marks and loss of histone demethylase protein persisted for at least 48 hours after removing sodium tungstate from the culture. The increase in global histone methylation remained when cells were cultured in methionine-free media, indicating that the increased histone methylation did not depend upon any de novo methylation process, but rather was due to the loss of the demethylase protein. Similar increases of H3K4me3 and H3K9me2 were observed in the livers of the mice that were acutely exposed to tungstate via their drinking water. Taken together, our results indicated that tungstate exposure specifically reduced histone demethylase JARID1A and JMJD1A via proteasomal degradation, leading to increased histone methylation

BACKGROUND: The X-linked inhibitor of apoptosis protein (XIAP) is a well-known potent apoptosis suppressor and also participates in cancer cell biological behaviors, therefore attracting great attentions as a potential antineoplastic therapeutic target for past years. Anti-IAP therapy is reported to be closely related to epidermal growth factor receptor (EGFR) expression level. However, whether and how XIAP modulates EGFR expression remains largely unknown. METHODS: Human XIAP was knockdown with short-hairpin RNA in two different bladder cancer cell lines, T24T and UMUC3. Two XIAP mutants, XIAP BIR (deletion of N-terminal three BIR domains) and XIAP RING (deletion of C-terminal RING domain and keeping the function of BIR domains), were generated to determine which domain is involved in regulating EGFR. RESULTS: We found here that lacking of XIAP expression resulted in a remarkable suppression of EGFR expression, consequently leading to the deficiency of anchorage-independent cell growth. Further study demonstrated that BIR domain of XIAP was crucial for regulating the EGFR translation by suppressing the transcription and expression of miR-200a. Mechanistic studies indicated that BIR domain activated the protein phosphatase 2 (PP2A) activity by decreasing the phosphorylation of PP2A at Tyr307 in its catalytic subunit, PP2A-C. Such activated PP2A prevented the deviant phosphorylation and activation of MAPK kinases/MAPKs, their downstream effector c-Jun, and in turn inhibiting transcription of c-Jun-regulated the miR-200a. CONCLUSIONS: Our study uncovered a novel function of BIR domain of XIAP in regulating the EGFR translation, providing significant insight into the understanding of the XIAP overexpression in the cancer development and progression, further offering a new theoretical support for using XIAP BIR domain and EGFR as targets for cancer therapy.

The environmental and occupational carcinogen Hexavalent Chromium (Cr(VI)) has been shown to cause lung cancer in humans when inhaled. In spite of a considerable research effort, the mechanisms of Cr(VI)-induced carcinogenesis remain largely unknown. Nupr1 (nuclear protein 1) is a small, highly basic, and unfolded protein with molecular weight of 8,800 daltons and is induced by a variety of stressors. Studies in animal models have suggested that Nupr1 is a key factor in the development of lung and pancreatic cancers, with little known about the underlying molecular mechanisms. Here we report that the level of Nupr1 is significantly increased in human bronchial epithelial BEAS2B cells following exposure to Cr(VI) through epigenetic mechanisms. Interestingly, Cr(VI) exposure also results in the loss of acetylation at histone H4K16, which is considered a 'hallmark' of human cancer. Cr(VI)-induced reduction of H4K16 acetylation appears to be caused by the induction of Nupr1, since (a) overexpression of Nupr1 decreased the levels of both H4K16 acetylation and the histone acetyltransferase MOF (male absent on the first; also known as Kat8, Myst 1), which specifically acetylates H4K16; (b) the loss of acetylation of H4K16 upon Cr(VI) exposure is greatly compromised by knockdown of Nupr1. Moreover, Nupr1-induced reduction of H4K16 acetylation correlates with the transcriptional down-regulation at several genomic loci. Notably, overexpression of Nupr1 induces anchorage-independent cell growth and knockdown of Nupr1 expression prevents Cr(VI)-induced cell transformation. We propose that Cr(VI) induces Nupr1 and rapidly perturbs gene expression by downregulating H4K16 acetylation, thereby contributing to Cr(VI)-induced carcinogenesis.

Ultraviolet radiation (UVR) from sunlight is the primary effector of skin DNA damage. Chromatin remodeling and histone post-translational modification (PTM) are critical factors in repairing DNA damage and maintaining genomic integrity, however, the dynamic changes of histone marks in response to solar UVR are not well characterized. Here we report global changes in histone PTMs induced by solar simulated UVR (ssUVR). A decrease in lysine acetylation of histones H3 and H4, particularly at positions of H3 lysine 9, lysine 56, H4 lysine 5, and lysine 16, was found in human keratinocytes exposed to ssUVR. These acetylation changes were highly associated with ssUVR in a dose-dependent and time-specific manner. Interestingly, H4K16ac, a mark that is crucial for higher order chromatin structure, exhibited a persistent reduction by ssUVR that was transmitted through multiple cell divisions. In addition, the enzymatic activities of histone acetyltransferases were significantly reduced in irradiated cells, which may account for decreased global acetylation. Moreover, depletion of histone deacetylase SIRT1 in keratinocytes rescued ssUVR-induced H4K16 hypoacetylation. These results indicate that ssUVR affects both HDAC and HAT activities, leading to reduced histone acetylation.