miR-107 promotes tumor progression by targeting the let-7 microRNA in mice and humans.

MicroRNAs (miRNAs) influence many biological processes, including cancer. They do so by posttranscriptionally repressing target mRNAs to which they have sequence complementarity. Although it has been postulated that miRNAs can regulate other miRNAs, this has never been shown experimentally to our knowledge. Here, we demonstrate that miR-107 negatively regulates the tumor suppressor miRNA let-7 via a direct interaction. miR-107 was found to be highly expressed in malignant tissue from patients with advanced breast cancer, and its expression was inversely correlated with let-7 expression in tumors and in cancer cell lines. Ectopic expression of miR-107 in human cancer cell lines led to destabilization of mature let-7, increased expression of let-7 targets, and increased malignant phenotypes. In contrast, depletion of endogenous miR-107 dramatically increased the stability of mature let-7 and led to downregulation of let-7 targets. Accordingly, miR-107 expression increased the tumorigenic and metastatic potential of a human breast cancer cell line in mice via inhibition of let-7 and upregulation of let-7 targets. By mutating individual sites within miR-107 and let-7, we found that miR-107 directly interacts with let-7 and that the internal loop of the let-7/miR-107 duplex is critical for repression of let-7 expression. Altogether, we have identified an oncogenic role for miR-107 and provide evidence of a transregulational interaction among miRNAs in human cancer development.

Connective tissue growth factor confers drug resistance in breast cancer through concomitant up-regulation of Bcl-xL and cIAP1.

Connective tissue growth factor (CTGF) expression is elevated in advanced breast cancer and promotes metastasis. Chemotherapy response is only transient in most metastatic diseases. In the present study, we examined whether CTGF expression could confer drug resistance in human breast cancer. In breast cancer patients who received neoadjuvant chemotherapy, CTGF expression was inversely associated with chemotherapy response. Overexpression of CTGF in MCF7 cells (MCF7/CTGF) enhanced clonogenic ability, cell viability, and resistance to apoptosis on exposure to doxorubicin and paclitaxel. Reducing the CTGF level in MDA-MB-231 (MDA231) cells by antisense CTGF cDNA (MDA231/AS cells) mitigated this drug resistance capacity. CTGF overexpression resulted in resistance to doxorubicin- and paclitaxel-induced apoptosis by up-regulation of Bcl-xL and cellular inhibitor of apoptosis protein 1 (cIAP1). Knockdown of Bcl-xL or cIAP1 with specific small interfering RNAs abolished the CTGF-mediated resistance to apoptosis induced by the chemotherapeutic agents in MCF7/CTGF cells. Inhibition of extracellular signal-regulated kinase (ERK)-1/2 effectively reversed the resistance to apoptosis as well as the up-regulation of Bcl-xL and cIAP1 in MCF7/CTGF cells. A neutralizing antibody against integrin alpha(v)beta(3) significantly attenuated CTGF-mediated ERK1/2 activation and up-regulation of Bcl-xL and cIAP1, indicating that the integrin alpha(v)beta(3)/ERK1/2 signaling pathway is essential for CTGF functions. The Bcl-xL level also correlated with the CTGF level in breast cancer patients. We also found that a COOH-terminal domain peptide from CTGF could exert activities similar to full-length CTGF, in activation of ERK1/2, up-regulation of Bcl-xL/cIAP1, and resistance to apoptosis. We conclude that CTGF expression could confer resistance to chemotherapeutic agents through augmenting a survival pathway through ERK1/2-dependent Bcl-xL/cIAP1 up-regulation.

Helioxanthin inhibits interleukin-1 beta-induced MIP-1 beta production by reduction of c-jun expression and binding of the c-jun/CREB1 complex to the AP-1/CRE site of the MIP-1 beta promoter in Huh7 cells.

An elevated level of macrophage inflammatory protein-1beta (MIP-1beta) induced by IL-1beta has been correlated with chronic hepatic inflammatory disease. However, molecular mechanism of IL-1beta-induced MIP-1beta expression in hepatic cells is obscure. Previously, we reported the mechanism of the anti-hepatitis B virus (HBV) activity of helioxanthin (HE-145). Here, we demonstrated that HE-145 inhibited IL-1beta-induced MIP-1beta expression in a dose-dependent manner in Huh7 cells. To understand the mode of action of HE-145, we first examined how IL-1beta induced MIP-1beta expression at the molecular level. Using selective inhibitors, we found that JNK and p38 pathways participated in IL-1beta-induced MIP-1beta expression. HE-145 specifically suppressed IL-1beta-induced c-jun mRNA and protein expression and prevented c-jun-mediated AP-1 DNA-binding activity, whereas it had no effect on IL-1beta-induced activation of JNK, p38 and ATF2. Further studies indicated that HE-145 may downregulate c-jun mRNA expression directly at transcriptional level without requirement of de novo protein synthesis. Mutational analysis and supershift assays indicated that IL-1beta stimulated c-jun and CREB1 binding to the essential AP-1/CRE site of the MIP-1beta promoter. The inhibitory effect of HE-145 on IL-1beta-induced MIP-1beta promoter activity was completely reversed by overexpressing c-jun. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay consistently revealed that HE-145 reduced c-jun binding to the AP-1/CRE site in vitro and in vivo. Our results established a major role for c-jun in IL-1beta-induced MIP-1beta expression in hepatic cells. The reduction in IL-1beta-induced c-jun expression and subsequent binding of the c-jun/CREB1 complex to AP-1/CRE site mainly contributed to the inhibitory action of HE-145 on IL-1beta-induced MIP-1beta production.