Mouse Wee1 gene is repressed by Krüppel-like factor 3 (KLF3) via interaction with multiple upstream elements

miR-21-5p Regulates the Proliferation and Differentiation of Skeletal Muscle Satellite Cells by Targeting KLF3 in Chicken

The proliferation and differentiation of skeletal muscle satellite cells (SMSCs) play an important role in the development of skeletal muscle. Our previous sequencing data showed that miR-21-5p is one of the most abundant miRNAs in chicken skeletal muscle. Therefore, in this study, the spatiotemporal expression of miR-21-5p and its effects on skeletal muscle development of chickens were explored using in vitro cultured SMSCs as a model. The results in this study showed that miR-21-5p was highly expressed in the skeletal muscle of chickens. The overexpression of miR-21-5p promoted the proliferation of SMSCs as evidenced by increased cell viability, increased cell number in the proliferative phase, and increased mRNA and protein expression of proliferation markers including PCNA, CDK2, and CCND1. Moreover, it was revealed that miR-21-5p promotes the formation of myotubes by modulating the expression of myogenic markers including MyoG, MyoD, and MyHC, whereas knockdown of miR-21-5p showed the opposite result. Gene prediction and dual fluorescence analysis confirmed that KLF3 was one of the direct target genes of miR-21-5p. We confirmed that, contrary to the function of miR-21-5p, KLF3 plays a negative role in the proliferation and differentiation of SMSCs. Si-KLF3 promotes cell number and proliferation activity, as well as the cell differentiation processes. Our results demonstrated that miR-21-5p promotes the proliferation and differentiation of SMSCs by targeting KLF3. Collectively, the results obtained in this study laid a foundation for exploring the mechanism through which miR-21-5p regulates SMSCs.

Epigenetic silencing of Kruppel like factor-3 increases expression of pro-metastatic miR-182

Accumulating evidence indicates that microRNAs (miRs) regulate cancer metastasis. We have shown that miR-182 drives sarcoma metastasis in vivo by coordinated regulation of multiple genes. Recently, we also demonstrated that in a subset of primary sarcomas that metastasize to the lung, miR-182 expression is elevated through binding of MyoD1 to the miR-182 promoter. However, it is not known if there are also transcription factors that inhibit miR-182 expression. Defining negative regulators of miR-182 expression may help explain why some sarcomas do not metastasize and may also identify pathways that can modulate miR-182 for therapeutic benefit. Here, we use an in silico screen, chromatin-immunoprecipitation, and luciferase reporter assays to discover that Kruppel like factor-3 (Klf-3) is a novel transcriptional repressor of miR-182. Knockdown of Klf-3 increases miR-182 expression, and stable overexpression of Klf-3, but not a DNA-binding mutant Klf-3, decreases miR-182 levels. Klf-3 expression is downregulated in both primary mouse and human metastatic sarcomas, and Klf-3 levels negatively correlate with miR-182 expression. Interestingly, Klf-3 also negatively regulates MyoD1, suggesting an alternative mechanism for Klf-3 to repress miR-182 expression in addition to direct binding of the miR-182 promoter. Using Methylation Specific PCR (MSP) and pyrosequencing assays, we found that Klf-3 is epigenetically silenced by DNA hypermethylation both in mouse and human sarcoma cells. Finally, we show the DNA methylation inhibitor 5'Azacytidine (Aza) restores Klf-3 expression while reducing miR-182 levels. Thus, our findings suggest that demethylating agents could potentially be used to modulate miR-182 levels as a therapeutic strategy.

Interplay between two myogenesis-related proteins: TBP-interacting protein 120B and MyoD

Gene expression in myogenesis is governed by multiple myogenic factors including MyoD. Previously, we demonstrated that TBP-interacting protein 120B (TIP120B) promotes in vitro myogenesis through its anti-ubiquitination ability. In this study, we investigated interplay between MyoD and TIP120B. Mouse C2C12 cells subjected to myotube differentiation contained increased amounts of TIP120B and MyoD. Dexamethasone, which inhibits myogenic signaling, decreased the amounts of those proteins. Mouse and human TIP120B promoters, which carry multiple E-box motifs, were potentiated by MyoD. In the human TIP120B, a proximal E-box binds to MyoD in vitro and exhibits MyoD-dependent transcription activation function. Expression of the endogenous TIP120B gene was correlated with the level of MyoD in different types of muscle-related cells. Furthermore, MyoD binds specifically to a proximal E-box-carrying promoter region in chromatin. Proteasome-sensitive MyoD was increased and decreased by overexpression and knockdown of TIP120B, respectively. Moreover, stability of MyoD was increased by TIP120B. The results suggest that MyoD and TIP120B potentiate each other at gene expression and post-translation levels, respectively, which may promote myogenesis cooperatively.