Friend or Foe: A Cancer Suppressor MicroRNA-34 Potentially Plays an Adverse Role in Vascular Diseases by Regulating Cell Apoptosis and Extracellular Matrix Degradation.

BACKGROUND MicroRNAs (miRNAs) have emerged as central regulators of many processes. MiRNA-34 (miR-34) functions as a well-known tumor suppressor. The aim of this study was to investigate the mechanisms underlying how miR-34 participates in vascular disorders. MATERIAL AND METHODS Three miR-34 family members (miR-34a, miR-34b, and miR-34c) were overexpressed or silenced in human vascular smooth muscle cells (VSMCs) and umbilical vein endothelial cells (UVECs), respectively, before the proliferation and apoptosis of cells were detected by using Cell Counting Kit-8 assay and Annexin V- fluorescein isothiocyanate/propidium iodide flow cytometry. The protein expression of apoptosis biomarkers was detected by western blot. Dual-luciferase reporter assay was performed to determine the candidate target of miR-34, and enzyme-linked immune sorbent assay was used to evaluate the effect of miR-34 on the expression of the target gene. RESULTS Overexpression of miR-34 family members repressed proliferation and promoted apoptosis of VSMCs and UVECs, whereas miR-34 knockdown led to the opposite results. In addition, miR-34a inhibited the expression of alpha-1 antitrypsin (AAT), a serine protease inhibitor that suppresses the degradation of extracellular matrix, through a miR-34-binding site within the 3'-UTR of AAT. CONCLUSIONS MiR-34 promoted apoptosis of VSMC and UVEC cells by inhibiting AAT expression. This finding provides an update on the understanding of the clinical value of miR-34, which might assist to uncover novel and effective therapeutic strategies for the treatment of vascular diseases.

IFN-γ-mediated downregulation of LXA4 is necessary for the maintenance of nonresolving inflammation and papilloma persistence.

Nonresolving inflammation is a hallmark of many types of tumors and the molecular mechanisms maintaining this inflammation are still largely unknown. In a two-stage carcinogenesis model, we observed here that the lack of IFN-γ receptor or neutralization of IFN-γ accelerated spontaneous papilloma regression in mice. The impaired maintenance of local inflammation was associated with reduced IFN-γ and enhanced biosynthesis of proresolution lipid mediator lipoxin A4 (LXA4). Interestingly, blocking LXA4 eliminated the effect of anti-IFN-γ, whereas treatment of mice with a therapeutic dose of LXA4 accelerated papilloma regression in an IFN-γ-independent manner. These results link for the first time a cytokine-dependent maintenance of inflammation with a downregulated production of proresolution lipid mediators. Strategies promoting spontaneous resolution of chronic inflammation by blocking IFN-γ and/or increasing LXA4 may be useful for the treatment of inflammation-associated tumors.

FSP1+ fibroblasts promote skin carcinogenesis by maintaining MCP-1-mediated macrophage infiltration and chronic inflammation.

Cancer development is often associated with increased fibroblast proliferation and extensive fibrosis; however, the role of fibroblasts during carcinogenesis remains largely unknown. Using the 7,12-dimethylbenz-(a)anthracene and 12-O-tetradecanoylphorbol-13-acetate-induced two-stage skin carcinogenesis model, we demonstrated here that there was a massive accumulation and proliferation of fibroblasts in the skin shortly after application of carcinogen. Selective abatement of these cells during the promotion stage drastically decreased incidence and progression of papillomas. This correlated well with reduced macrophage infiltration and impaired cytokine storm in the affected skin. 12-O-tetradecanoylphorbol-13-acetate stimulated skin fibroblasts, secreting high levels of monocyte chemotactic protein-1, and neutralization of this chemokine eliminated almost completely the fibroblast-induced chemotaxis of macrophages. These results strongly suggest that fibroblasts promote skin tumor development by producing monocyte chemotactic protein-1 and maintaining chronic inflammation.

IFNgamma promotes papilloma development by up-regulating Th17-associated inflammation.

IFNgamma plays a crucial role in immunity against a variety of transplanted tumors and methylcholanthrene-mediated tumorigenesis in mice. However, it is not clear whether and how endogenous IFNgamma influences 7,12-dimethylbenz(a)anthracene (DMBA)-induced and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced papilloma development. We found here that IFNgamma expression was markedly up-regulated shortly after DMBA/TPA application to the skin. Surprisingly, neutralizing IFNgamma activity in vivo did not increase but rather decreased tumor development. Furthermore, IFNgamma receptor-deficient mice were also more resistant to papilloma development than their counterparts were. IFNgamma acted mainly in the promotion stage of papilloma development by enhancing TPA-induced leukocyte infiltration and epidermal hyperproliferation. The up-regulation of tumor necrosis factor alpha, interleukin (IL)-6, and transforming growth factor beta was largely dependent on host IFNgamma responsiveness. Remarkably, up-regulation of both IL-17 expression in the skin and T helper 17 (Th17) cell number in draining lymph nodes after DMBA/TPA treatment was dependent on IFNgamma signaling. Depletion of IL-17 not only decreased the DMBA/TPA-induced inflammation and keratinocyte proliferation but also delayed papilloma development. These results show that IFNgamma, under certain conditions, may promote tumor development by enhancing a Th17-associated inflammatory reaction.

Endogenous interleukin-4 promotes tumor development by increasing tumor cell resistance to apoptosis.

The increase of interleukin-4 (IL-4) level in tumor environment and the up-regulation of IL-4 receptor (IL-4R) on tumor cells have been long observed. However, their significance for tumor development has not been investigated. Here, we found that endogenous IL-4 promotes tumor growth because neutralizing IL-4 by 11B11 monoclonal antibody (mAb) significantly delayed the growth of MCA205 fibrosarcoma. We also observed that tumor cells with higher IL-4R expression have more chances to survive in immunocompetent mice. To investigate how endogenous IL-4 influences tumor growth, we established a pair of tumor cells with or without IL-4R expression from the common parental cells. IL-4R-competent tumors exhibit increased growth compared with its IL-4R-deficient counterparts when inoculated into syngeneic mice. This growth advantage was still kept in IL-4R knockout mice but was abrogated in mice given i.p. with IL-4 neutralizing mAb. In vitro analyses indicate that IL-4 neither affects the proliferation of tumor cells nor changes the expression of several immune-related molecules, such as MHC-I, Fas, and B7-H3. Nonetheless, IL-4 up-regulates antiapoptotic gene expression in tumor cells and reduces apoptosis of tumor cells in vivo, as evidenced by real-time PCR, immunoblotting, and TUNEL staining. These findings were helpful to understand the long clinical observation and revealed that endogenous IL-4, the product of host immune response, can be used by tumor cells to facilitate their growth.