MicroRNAs involved in keratinocyte migration and wound healing are largely unknown. Here, we revealed the indispensable role of miR-21 in keratinocyte migration and in re-epithelialization during wound healing in mice. In HaCaT cell, miR-21 could be upregulated by TGF-β1. Similar to the effect of TGF-β1, miR-21 overexpression promoted keratinocyte migration. Conversely, miR-21 knockdown attenuated TGF-β1-induced keratinocyte migration, suggesting that miR-21 was essential for TGF-β-driven keratinocyte migration. Furthermore, we found that miR-21 was upregulated during wound healing, coincident with the temporal expression pattern of TGF-β1. Consistently, knockdown of endogenous miR-21 using a specific antagomir dramatically delayed re-epithelialization possibly due to the reduced keratinocyte migration. TIMP3 and TIAM1, direct targets of miR-21, were verified to be regulated by miR-21 in vitro and in vivo, indicating that these two molecules might contribute to miR-21-induced keratinocyte migration. Taken together, our results demonstrate that miR-21 promotes keratinocyte migration and boosts re-epithelialization during skin wound healing.

Recent studies have begun to reveal critical roles of microRNAs (miRNAs) in the pathogenesis of cardiac hypertrophy and dysfunction. In this study, we tested whether a transforming growth factor-β (TGF-β)-regulated miRNA played a pivotal role in the development of cardiac hypertrophy and heart failure (HF). We observed that miR-27b was upregulated in hearts of cardiomyocyte-specific Smad4 knockout mice, which developed cardiac hypertrophy. In vitro experiments showed that the miR-27b expression could be inhibited by TGF-β1 and that its overexpression promoted hypertrophic cell growth, while the miR-27b suppression led to inhibition of the hypertrophic cell growth caused by phenylephrine (PE) treatment. Furthermore, the analysis of transgenic mice with cardiomyocyte-specific overexpression of miR-27b revealed that miR-27b overexpression was sufficient to induce cardiac hypertrophy and dysfunction. We validated the peroxisome proliferator-activated receptor-γ (PPAR-γ) as a direct target of miR-27b in cardiomyocyte. Consistently, the miR-27b transgenic mice displayed significantly lower levels of PPAR-γ than the control mice. Furthermore, in vivo silencing of miR-27b using a specific antagomir in a pressure-overload-induced mouse model of HF increased cardiac PPAR-γ expression, attenuated cardiac hypertrophy and dysfunction. The results of our study demonstrate that TGF-β1-regulated miR-27b is involved in the regulation of cardiac hypertrophy, and validate miR-27b as an efficient therapeutic target for cardiac diseases.

Merkel cell carcinoma (MCC) is a rare and aggressive, yet highly immunogenic skin cancer. The latter is due to its viral or UV-associated carcinogenesis. For tumor progression MCC has to escape the host’s immuno-surveillance, e.g. by loss of HLA class-I expression. Indeed, a reduced HLA class-I expression was observed in MCC tumor tissues and MCC cell lines. This reduced HLA class-I surface expression is caused by an impaired expression of key components of the antigen processing machinery (APM), including LMP2 and LMP7 as well as TAP1 and TAP2. Notably, experimental provisions of HLA class-I binding peptides restored HLA class-I surface expression on MCC cells. Silencing of the HLA class-I APM is due to histone deacetylation as inhibition of histone deacetylases (HDACs) not only induced acetylation of histones in the respective promoter regions but also re-expression of APM components. Thus, HDAC inhibition restored HLA class-I surface expression in vitro and in a mouse xenotransplantation model. In contrast to re-induction of HLA class-I by interferons, HDAC inhibitors did not interfere with the expression of immuno-dominant viral proteins. In summary, restoration of HLA class-I expression on MCC cells by epigenetic priming is an attractive approach to enhance therapies boosting adaptive immune responses.

Circulating cell-free miR-375 proved as a surrogate marker for tumor burden in MCC without restriction to polyomavirus positivity; it thus appears to be useful for therapy monitoring and the follow-up of patients with MCC.

Accumulating evidence has shown that miRNAs are aberrantly expressed in human gastric cancer and crucial to tumorigenesis. Herein, we identified the role of miR-148a in gastric cell proliferation. miR-148a knockdown inhibited cell proliferation in gastric cancer cell lines. Conversely, miR-148a overexpression promoted cell proliferation and cell cycle progression. p27, a key inhibitor of cell cycle, was verified as the target of miR-148a, indicating miR-148a might downregulate p27 expression to promote gastric cell proliferation. Moreover, we confirmed that miR-148a expression was frequently and dramatically downregulated in human advanced gastric cancer tissues, and observed a good inverse correlation between miR-148a and p27 expression in tumor samples. Thus, our results demonstrated that miR-148a downregulation might exert some sort of antagonistic function in cell proliferation, rather than promote cell proliferation in gastric cancer.

The transforming growth factor-β (TGF-β) signalling pathway participates in various biological processes. Dysregulation of Smad4, a central cellular transducer of TGF-β signalling, is implicated in a wide range of human diseases and developmental disorders. However, the mechanisms underlying Smad4 dysregulation are not fully understood. Using a functional screening approach based on luciferase reporter assays, we identified 39 microRNAs (miRNAs) as potential regulators of Smad4 from an expression library of 388 human miRNAs. The screening was supported by bioinformatic analysis, as 24 of 39 identified miRNAs were also predicted to target Smad4. MiR-199a, one of the identified miRNAs, was inversely correlated with Smad4 expression in various human cancer cell lines and gastric cancer tissues, and repressed Smad4 expression and blocked canonical TGF-β transcriptional responses in cell lines. These effects were dependent on the presence of a conserved, but not perfect seed paired, miR-199a-binding site in the Smad4 3′-untranslated region (UTR). Overexpression of miR-199a significantly inhibited the ability of TGF-β to induce gastric cancer cell growth arrest and apoptosis in vitro, and promoted anchorage-independent growth in soft agar, suggesting that miR-199a plays an oncogenic role in human gastric tumourigenesis. In conclusion, our functional screening uncovers multiple miRNAs that regulate the cellular responsiveness to TGF-β signalling and reveals important roles of miR-199a in gastric cancer by directly targeting Smad4.

No abstract

Despite the fact that the transcription factor ATOH1 is a master regulator of Merkel cell development, its role in Merkel cell carcinoma (MCC) carcinogenesis remains controversial. Here, we provide several lines of evidence that ATOH1 is a lineage-dependent oncogene in MCC. Luciferase assays revealed binding of ATOH1 and subsequent activation to the promoter of miR-375, which is one of the most abundant microRNAs in MCCs. Overexpression of ATOH1 in variant MCC cell lines and fibroblasts induced miR-375 expression, whereas ATOH1 knockdown in classical MCC cell lines reduced miR-375 expression. Moreover, ATOH1 overexpression in these cells changed their growth characteristics from adherent to suspension and/orspheroidal growth, that is, resembling the neuroendocrine growth pattern of classical MCC cell lines. Notably, ectopic expression of different Merkel cell polyomavirus (MCPyV)-derived truncated large T antigens induced ATOH1 expression in fibroblasts, which was paralleled by miR-375 expression and similar morphologic changes. In summary, MCPyVassociated carcinogenesis is likely to induce the characteristic neuroendocrine features of MCC via induction of ATOH1; thus, ATOH1 can be regarded as a lineage-dependent oncogene in MCC.