The MicroRNA let-7a modulates interleukin-6-dependent STAT-3 survival signaling in malignant human cholangiocytes.
ABSTRACT The inflammation-associated cytokine interleukin-6 (IL-6) can contribute to tumor growth and resistance to therapy by the activation of survival mechanisms. In several human cancers, IL-6-activated survival signaling involves the signal transducers and activators of transcription (Stat) factors or protein kinase cascades. microRNAs (miRNAs) are endogenous regulators of gene expression that are altered in expression in many cancers. However, the effect of inflammatory cytokines on miRNA expression and the role of miRNA in modulating IL-6-mediated cell survival are unknown. We investigated the involvement of miRNA in malignant cholangiocytes stably transfected to overexpress IL-6, which enhances tumor growth in vivo by inhibition of apoptosis. We provide evidence that (i) miRNA expression both in vitro and in vivo is altered by overexpression of IL-6; (ii) selective miRNAs including let-7a are up-regulated and contribute to the survival effects of enforced IL-6 activity; and (iii) let-7a contributes to the constitutively increased phosphorylation of Stat-3 by a mechanism involving the neurofibromatosis 2 (NF2) gene. These findings reveal a novel mechanism by which IL-6 mediates tumor cell survival that may be therapeutically targeted and emphasize the presence of complex interrelationships between deregulated expression of miRNA and transcription factors in human cancers.
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ABSTRACT: Interleukin-6 (IL-6) is a proinflammatory cytokine that exerts a wide range of cellular, physiological, and pathophysiological responses. Pyrrolidine dithiocarbamate (PDTC) antagonizes the cellular responsiveness to IL-6 through impairment in signal transducer and activator of transcription-3 activation and downstream signaling. To further elucidate the biological properties of PDTC, global gene expression profiling of human HepG2 hepatocellular carcinoma cells was carried out after treatment with PDTC or IL-6 for up to 8 h. Through an unbiased pathway analysis method, gene array analysis showed dramatic and temporal differences in expression changes in response to PDTC versus IL-6. A significant number of genes associated with metabolic pathways, inflammation, translation, and mitochondrial function were changed, with ribosomal protein genes and DNA damage-inducible transcript 4 protein (DDIT4) primarily up-regulated with PDTC but down-regulated with IL-6. Quantitative polymerase chain reaction and Western blot analyses validated the microarray data and showed the reciprocal expression pattern of the mammalian target of rapamycin (mTOR)-negative regulator DDIT4 in response to PDTC versus IL-6. Cell treatment with PDTC resulted in a rapid and sustained activation of Akt and subsequently blocked the IL-6-mediated increase in mTOR complex 1 function through up-regulation in DDIT4 expression. Conversely, down-regulation of DDIT4 with small interfering RNA dampened the capacity of PDTC to block IL-6-dependent mTOR activation. The overall protein biosynthetic capacity of the cells was severely blunted by IL-6 but increased in a rapamycin-independent pathway by PDTC. These results demonstrate a critical effect of PDTC on mTOR complex 1 function and provide evidence that PDTC can reverse IL-6-related signaling via induction of DDIT4.Journal of Pharmacology and Experimental Therapeutics 09/2011; 339(3):905-13. DOI:10.1124/jpet.111.185678 · 3.86 Impact Factor
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ABSTRACT: MicroRNA (miRNA) has emerged as key post-transcriptional regulator and through this mechanism control many normal developmental and physiological processes. Conversely, aberrant expression of some miRNAs has been correlated with various disorders, more specifically, development and progression of malignancy. Endometrium is a dynamic tissue which undergoes extensive cyclic changes in preparation for embryo implantation during reproductive years, as well as changes that occur following menopause, and establishment of benign and malignant uterine disorders. These processes are highly regulated by ovarian steroids and locally expressed genes in response to steroid hormone receptor-mediated signaling and include genes related to inflammatory reaction, apoptosis, cell-cycle progression, angiogenesis and tissue remodeling. Here we present an overview of our current understanding of uterine miRNA biogenesis and highlights their potential regulatory functions in cellular processes relevant to normal uterine physiological and pathological disorders such as endometriosis, dysfunctional uterine bleeding and endometrial cancer. Understanding the expression, regulation and functional aspects of miRNAs in uterine environment under normal and various disorders may lead to their potential utilization as diagnostic as well as therapeutic tool.Animal reproduction 01/2010; 7(3):117-128.
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ABSTRACT: Apoptosis is a tightly regulated form of cell death and represents an important process during normal development. In the past years, the scientific community has produced remarkable advances in our understanding of cancer biology, realizing that apoptosis and the genes that control it have a profound effect on the malignant phenotype. Recently, a new class of non-coding RNA genes, known as microRNA (miRNA or miR), have been demonstrated to play important roles in diverse biological processes, including development, cell differentiation, proliferation, and apoptosis. This suggests that other oncogenic mechanisms are needed to produce selective pressure to override apoptosis during multistage carcinogenesis. Intriguingly, since most cytotoxic anticancer agents induce apoptosis, it is possible that defects in apoptotic programs may contribute to treatment failure. Several studies strongly suggest a role for microRNAs in modulating sensitive/resistant phenotypes to cytotoxic therapy, calling for further investigation and validation of microRNA functions and targets in order to improve sensitivity to cancer treatments, thus ultimately improving prognosis and survival. Here, we review the current findings about microRNAs focusing on their involvement in the apoptotic process.Endocrine Related Cancer 10/2009; 17(1):F37-50. DOI:10.1677/ERC-09-0163 · 4.91 Impact Factor