Hara Kang

Bone Morphogenetic Protein 4 Promotes Vascular Smooth Muscle Contractility by Activating MicroRNA-21 (miR-21), which Down-regulates Expression of Family of Dedicator of Cytokinesis (DOCK) Proteins

Background: miR-21 expression is regulated by BMP4 and plays a critical role in vSMC phenotype regulation. Results: Affinity purification of mRNAs associated with miR-21 yielded nearly all members of the DOCK superfamily. Conclusion: miR-21 targets multiple members of the DOCK superfamily and modulates the activity of Rac1 small GTPase to regulate vSMC phenotype. Significance: This study identified novel targets of miR-21 using a biochemical method. The bone morphogenetic protein 4 (BMP4) signaling pathway plays a critical role in the promotion and maintenance of the contractile phenotype in vascular smooth muscle cell (vSMC). Misexpression or inactivating mutations of the BMP receptor gene can lead to dedifferentiation of vSMC characterized by increased migration and proliferation that is linked to vascular proliferative disorders. Previously we demonstrated that vSMCs increase microRNA-21 (miR-21) biogenesis upon BMP4 treatment, which induces contractile gene expression by targeting programmed cell death 4 (PDCD4). To identify novel targets of miR-21 that are critical for induction of the contractile phenotype by BMP4, biotinylated miR-21 was expressed in vSMCs followed by an affinity purification of mRNAs associated with miR-21. Nearly all members of the dedicator of cytokinesis (DOCK) 180-related protein superfamily were identified as targets of miR-21. Down-regulation of DOCK4, -5, and -7 by miR-21 inhibited cell migration and promoted cytoskeletal organization by modulating an activity of small GTPase. Thus, this study uncovers a regulatory mechanism of the vSMC phenotype by the BMP4-miR-21 axis through DOCK family proteins.

MicroRNA regulation of smooth muscle gene expression and phenotype.

Purpose of reviewIn this review, we summarize the recent advances regarding microRNA (miRNA) functions in the regulation of vascular smooth muscle cell (VSMC) differentiation and phenotypic modulation. Recent findingsMultiple miRNAs are found to be responsible for VSMC differentiation and proliferation under physiological or pathological condition. A single miRNA downregulates multiple targets, whereas a single gene is regulated by multiple miRNAs to modulate a specific aspect of VSMC phenotype. SummaryThe phenotype of VSMCs is dynamically regulated in response to environmental stimuli. Deregulation of phenotype switching is associated with vascular diseases. Several miRNAs have been found to be highly expressed in the vasculature, to modulate VSMC phenotype, and to be dysregulated in vascular diseases. By regulating mRNA and/or protein levels posttranscriptionally, miRNAs provide a delicate regulation in the complex molecular networks that regulate the vascular system. Understanding the functions of miRNAs in the regulation of VSMC differentiation and phenotype switching provides new insights into the mechanisms of vascular development, function, and dysfunction.

Inhibition of MicroRNA-302 (miR-302) by Bone Morphogenetic Protein 4 (BMP4) Facilitates the BMP Signaling Pathway

Background: The BMP signaling pathway modulates the expression of protein coding genes and non-coding RNAs. Results: BMP4-Smad pathway represses the transcription of miR-302∼367 cluster and depresses the expression of the type II BMP receptor. Conclusion: BMP4 treatment facilitates the BMP signaling pathway by down-regulation of miR-302. Significance: Autoregulatory mechanism of control of BMP signaling pathway via miRNA and its target. The signaling pathway mediated by BMPs plays an essential role during development as well as the maintenance of homeostasis in adult. Aberrant activation or inactivation of BMP signaling can lead to developmental defects and various human disorders. To fine-tune its activity, BMP signaling is regulated both positively and negatively by extrinsic and intrinsic regulatory factors that modulate binding of ligand to the receptors, and the activity of receptors and their dedicated signal transducers, the Smad proteins. Upon BMP binding to the receptor complex, Smad proteins translocate to the nucleus and modulate gene expression transcriptionally by directly associating with the promoter region of target genes, or post-transcriptionally through modulation of microRNA (miRNA) synthesis. In this study, we demonstrate that BMP signaling down-regulates transcription of the miRNA-302∼367 gene cluster. We show that the type II BMP receptor (BMPRII) is a novel target of miR-302. Upon overexpression, miR-302 targets a partially complementary sequence localized in the 3′-untranslated region (UTR) of BMPRII transcripts and leads to destabilization of the transcripts and down-regulation of BMP signaling. We propose that the negative regulatory loop of BMP4-miR-302-BMPRII is a potential mechanism for the maintenance and fine-tuning of the BMP signaling pathway in various systems.

The role of microRNAs in cell fate determination of mesenchymal stem cells : balancing adipogenesis and osteogenesis

Mesenchymal stem cells (MSCs) are multipotent stem cells capable of differentiating into adipocytes, osteoblasts, or chondrocytes. A mutually inhibitory relationship exists between osteogenic and adipogenic lineage commitment and differentiation. Such cell fate decision is regulated by several signaling pathways, including Wnt and bone morphogenetic protein (BMP). Accumulating evidence indicates that microRNAs (miRNAs) act as switches for MSCs to differentiate into either osteogenic or adipogenic lineage. Different miRNAs have been reported to regulate a master transcription factor for osteogenesis, such as Runx2, as well as molecules in the Wnt or BMP signaling pathway, and control the balance between osteoblast and adipocyte differentiation. Here, we discuss recent advancement of the cell fate decision of MSCs by miRNAs and their targets. [BMB Reports 2015; 48(6): 319-323]

Down-regulation of miR-96 by bone morphogenetic protein signaling is critical for vascular smooth muscle cell phenotype modulation.

The bone morphogenetic protein (BMP) signaling pathway is critical for the induction and maintenance of contractile phenotype in vascular smooth muscle cells (VSMCs). Inactivation of BMP signaling is common in abnormalities in vascular development and in vascular proliferative conditions, such as pulmonary artery hypertension. Herein, we identify microRNA‐96 (miR‐96) as a modulator of the VSMC phenotype in response to BMP4 signaling. We show that miR‐96 is down‐regulated by BMP4 treatment, which results in the derepression of a novel target, Tribbles‐like protein 3 (Trb3). miR‐96 targets a partially complementary sequence localized in the 3′ UTR of Trb3. Trb3 is an essential positive regulator of the BMP signaling pathway and promotes contractile phenotype in VSMCs. In conclusion, our study demonstrates a novel mechanism of regulation of SMC‐specific gene expression and induction of a VSMC contractile phenotype by the BMP4 signaling pathway via suppression of the miR‐96‐Trb3 axis. J. Cell. Biochem. 115: 889–895, 2014.

The Amiloride Derivative Phenamil Attenuates Pulmonary Vascular Remodeling by Activating NFAT and the Bone Morphogenetic Protein Signaling Pathway

ABSTRACT Pulmonary artery hypertension (PAH) is characterized by elevated pulmonary artery resistance and increased medial thickness due to deregulation of vascular remodeling. Inactivating mutations of the BMPRII gene, which encodes a receptor for bone morphogenetic proteins (BMPs), are identified in ∼60% of familial PAH (FPAH) and ∼30% of idiopathic PAH (IPAH) patients. It has been hypothesized that constitutive reduction in BMP signal by BMPRII mutations may cause abnormal vascular remodeling by promoting dedifferentiation of vascular smooth muscle cells (vSMCs). Here, we demonstrate that infusion of the amiloride analog phenamil during chronic-hypoxia treatment in rat attenuates development of PAH and vascular remodeling. Phenamil induces Tribbles homolog 3 (Trb3), a positive modulator of the BMP pathway that acts by stabilizing the Smad family signal transducers. Through induction of Trb3, phenamil promotes the differentiated, contractile vSMC phenotype characterized by elevated expression of contractile genes and reduced cell growth and migration. Phenamil activates the Trb3 gene transcription via activation of the calcium-calcineurin-nuclear factor of activated T cell (NFAT) pathway. These results indicate that constitutive elevation of Trb3 by phenamil is a potential therapy for IPAH and FPAH.

Functions of the bone morphogenetic protein signaling pathway through microRNAs (Review)

MicroRNAs (miRNAs or miRs) have emerged as key regulators of gene expression in essential cellular processes, such as cell growth, differentiation and development. Recent findings have established that the levels of miRNAs are modulated by cell signaling mechanisms, including the bone morphogenetic protein (BMP) signaling pathway. The BMP signaling pathway controls diverse cellular activities by modulating the levels of miRNAs, indicating the complexity of gene regulation by the BMP signaling pathway. The tight regulation of the levels of miRNAs is critical for maintaining normal physiological conditions, and dysregulated miRNA levels contribute to the development of diseases. In the present review, we discuss different insights (provided over the past decade) into the regulation of miRNAs governed by the BMP signaling pathway and the implications of this regulation on the understanding of the cellular differentiation of vascular smooth muscle cells (VSMCs), osteoblasts and neuronal cells.

miR-142-3p Is a Regulator of the TGFβ-Mediated Vascular Smooth Muscle Cell Phenotype.

The transforming growth factor β (TGFβ) signaling pathway is critical for the promotion and maintenance of the contractile phenotype of vascular smooth muscle cells (VSMCs). Though multiple microRNAs (miRNAs) implicated in the regulation of the VSMC phenotype have been identified, the modulation of miRNAs in the VSMCs by TGFβ signaling has not been fully described. In this study, we identified microRNA‐142‐3p (miR‐142‐3p) as a modulator of the VSMC phenotype in response to TGFβ signaling. We show that miR‐142‐3p is induced upon TGFβ signaling, leading to the repression of a novel target, dedicator of cytokinesis 6 (DOCK6). The downregulation of DOCK6 by miR‐142‐3p is critical for cell migration. Thus, this study demonstrates that miR‐142‐3p is a key regulator of the TGFβ‐mediated contractile phenotype of VSMCs that acts through inhibiting cell migration through targeting DOCK6. J. Cell. Biochem. 116: 2325–2333, 2015.

Stat5 phosphorylation is responsible for the excessive potency of HB-EGF

Heparin‐binding EGF‐like growth factor (HB‐EGF) is a potent growth factor involved in wound healing and tumorigenesis. Despite the sequence similarity between HB‐EGF and EGF, HB‐EGF induces cellular proliferation and migration more potently than EGF. However, the differential regulation by HB‐EGF and EGF has not been thoroughly elucidated. In this study, we compared signaling pathways activated by HB‐EGF and EGF to understand the details of the molecular mechanism of the high potency induced by HB‐EGF. HB‐EGF specifically induced the phosphorylation of EGFR‐Y1045 and activated Stat5, which is responsible for promoting cell proliferation, and migration. The competition of phosphorylated EGFR‐Y1045 inhibited Stat5 activation and consequently lowered the effect of HB‐EGF on cell proliferation, suggesting that the phosphorylation of EGFR‐Y1045 is essential for the activation of Stat5. The phosphorylation of EGFR‐Y1045 and Stat5 induced by HB‐EGF was prevented by sequestering the heparin‐binding domain, suggesting that the heparin‐binding domain is critical for HB‐EGF‐mediated signaling and cellular responses. In conclusion, the heparin‐binding domain of HB‐EGF was responsible for EGFR‐mediated Stat5 activation, resulting in a more potent cellular proliferation, and migration than that mediated by EGF. This molecular mechanism is useful for understanding ligand‐specific EGFR signaling and developing biomedicines for wound healing or cancer therapy.