Activation of p53 After Irradiation Impairs the Regenerative Capacity of the Mouse Liver.

Radiation therapy is one of the treatment methods for hepatocellular carcinoma. However, radiation tolerance of the liver is low, and the detailed effect of radiation on liver regeneration has not been clarified. C57BL/6J mice or hepatocyte-specific p53 knockout (KO) mice (albumin [Alb]-Cre Trp53flox/flox ) were irradiated with a single fraction of 10 Gy localized to the upper abdomen. We performed 70% partial hepatectomy (PHx) 24 hours after irradiation. Liver regeneration was assessed by proliferation cell nuclear antigen (PCNA)- and Ki-67-positive hepatocyte ratios and liver-to-body weight ratio after PHx. To establish a fibrosis model, CCl4 was orally administered for 8 weeks. The murine hepatocyte cell line BNL CL.2 (CL2) was irradiated with 10 Gy. Irradiation activated p53, induced downstream p21 in the liver, and delayed liver regeneration after PHx. While PHx increased hepatocyte growth factor (HGF) levels and activated Met with or without irradiation in the regenerative liver, it activated Akt and extracellular kinase 1 and 2 (Erk 1/2) less in irradiated mice than in nonirradiated mice. In CL2 cells cultured with HGF, irradiation suppressed cell growth by decreasing phosphorylated Akt and Erk 1/2 levels, which was abolished by small interfering RNA-mediated p53 knockdown but not by p21 knockdown. Hepatocyte-specific knockout of p53 in mice abolished the irradiation-induced suppression of both liver regeneration and Akt and Erk 1/2 activation after PHx. In the fibrotic mouse model, the survival rate after PHx of irradiated p53 KO mice was higher than that of wild-type mice. Conclusion: p53 but not p21 is involved in the impaired regenerative ability of the irradiated liver.

Phosphorylation of slit diaphragm proteins NEPHRIN and NEPH1 upon binding of HGF promotes podocyte repair.

Phosphorylation (activation) and dephosphorylation (deactivation) of the slit diaphragm proteins NEPHRIN and NEPH1 are critical for maintaining the kidney epithelial podocyte actin cytoskeleton and, therefore, proper glomerular filtration. However, the mechanisms underlying these events remain largely unknown. Here we show that NEPHRIN and NEPH1 are novel receptor proteins for hepatocyte growth factor (HGF) and can be phosphorylated independently of the mesenchymal epithelial transition receptor in a ligand-dependent fashion through engagement of their extracellular domains by HGF. Furthermore, we demonstrate SH2 domain-containing protein tyrosine phosphatase-2-dependent dephosphorylation of these proteins. To establish HGF as a ligand, purified baculovirus-expressed NEPHRIN and NEPH1 recombinant proteins were used in surface plasma resonance binding experiments. We report high-affinity interactions of NEPHRIN and NEPH1 with HGF, although NEPHRIN binding was 20-fold higher than that of NEPH1. In addition, using molecular modeling we constructed peptides that were used to map specific HGF-binding regions in the extracellular domains of NEPHRIN and NEPH1. Finally, using an in vitro model of cultured podocytes and an ex vivo model of Drosophila nephrocytes, as well as chemically induced injury models, we demonstrated that HGF-induced phosphorylation of NEPHRIN and NEPH1 is centrally involved in podocyte repair. Taken together, this is the first study demonstrating a receptor-based function for NEPHRIN and NEPH1. This has important biological and clinical implications for the repair of injured podocytes and the maintenance of podocyte integrity.

VEGF-A, HGF and bFGF are Involved in IL-17A-mediated Migration and Capillary-like Vessel Formation of Vascular Endothelial Cells.

BACKGROUND: Interleukin (IL)-17A possesses biological activities to promote vascular endothelial cell migration and microvessel development. OBJECTIVE: To clarify which angiogenic factors are involved in IL-17A-modified angiogenesis-related functions of vascular endothelial cell migration and microtube development or not. METHODS: The potential contribution of various angiogenic stimulators to in vitro angiogenic activities of IL-17A was assessed with both modified Boyden Chemotaxicell chamber assay and in vitro angiogenesis assay. RESULTS: The addition of a neutralizing antibody (Ab) for hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF)-A to the upper and lower compartments in a modified Boyden Chemotaxicell chamber significantly attenuated human dermal microvascular endothelial cell (HMVEC) migration elicited by IL-17A. Moreover, IL-17A-induced capillary-like microvessel development in human umbilical vein endothelial cell (HUVEC) and human dermal fibroblast (HDF) co-culture system was significantly impaired by a neutralizing Ab against HGF, bFGF, VEGF-A, cysteine-x-cysteine ligand 8 (CXCL8)/IL-8 or cysteine-x-cysteine (CXC) chemokine receptor (CXCR)-2. CONCLUSION: Our findings demonstrate the involvement of HGF, bFGF, VEGF-A and/or CXCL8/IL-8, to various degrees, in migration and microvessel development of vascular endothelial cells mediated by IL-17A.

Organ-specific cholesterol metabolic aberration fuels liver metastasis of colorectal cancer.

Rationale: Metastasis, the development of secondary malignant growth at a distance from a primary tumor, is the main cause of cancer-associated death. However, little is known about how metastatic cancer cells adapt to and colonize in the new organ environment. Here we sought to investigate the functional mechanism of cholesterol metabolic aberration in colorectal carcinoma (CRC) liver metastasis. Methods: The expression of cholesterol metabolism-related genes in primary colorectal tumors (PT) and paired liver metastases (LM) were examined by RT-PCR. The role of SREBP2-dependent cholesterol biosynthesis pathway in cell growth and CRC liver metastasis were determined by SREBP2 silencing in CRC cell lines and experimental metastasis models including, intra-splenic injection models and liver orthotropic injection model. Growth factors treatment and co-culture experiment were performed to reveal the mechanism underlying the up-regulation of SREBP2 in CRC liver metastases. The in vivo efficacy of inhibition of cholesterol biosynthesis pathway by betulin or simvastatin were evaluated in experimental metastasis models. Results: In the present study, we identify a colorectal cancer (CRC) liver metastasis-specific cholesterol metabolic pathway involving the activation of SREBP2-dependent cholesterol biosynthesis, which is required for the colonization and growth of metastatic CRC cells in the liver. Inhibiting this cholesterol biosynthesis pathway suppresses CRC liver metastasis. Mechanically, hepatocyte growth factor (HGF) from liver environment activates SREBP2-dependent cholesterol biosynthesis pathway by activating c-Met/PI3K/AKT/mTOR axis in CRC cells. Conclusion: Our findings support the notion that CRC liver metastases show a specific cholesterol metabolic aberration. Targeting this cholesterol biosynthesis pathway could be a promising treatment for CRC liver metastasis.

HGF/c-Met regulates p22phox subunit of the NADPH oxidase complex in primary mouse hepatocytes by transcriptional and post-translational mechanisms.

INTRODUCTION AND OBJECTIVES: It is well-known that signaling mediated by the hepatocyte growth factor (HGF) and its receptor c-Met in the liver is involved in the control of cellular redox status and oxidative stress, particularly through its ability to induce hepatoprotective gene expression by activating survival pathways in hepatocytes. It has been reported that HGF can regulate the expression of some members of the NADPH oxidase family in liver cells, particularly the catalytic subunits and p22phox. In the present work we were focused to characterize the mechanism of regulation of p22phox by HGF and its receptor c-Met in primary mouse hepatocytes as a key determinant for cellular redox regulation. MATERIALS AND METHODS: Primary mouse hepatocytes were treated with HGF (50 ng/mL) at different times. cyba expression (gene encoding p22phox) or protein content were addressed by real time RT-PCR, Western blot or immunofluorescence. Protein interactions were explored by immunoprecipitation and FRET analysis. RESULTS: Our results provided mechanistic information supporting the transcriptional repression of cyba induced by HGF in a mechanism dependent of NF-κB activity. We identified a post-translational regulation mechanism directed by p22phox degradation by proteasome 26S, and a second mechanism mediated by p22phox sequestration by c-Met in plasma membrane. CONCLUSION: Our data clearly show that HGF/c-Met exerts regulation of the NADPH oxidase by a wide-range of molecular mechanisms. NADPH oxidase-derived reactive oxygen species regulated by HGF/c-Met represents one of the main mechanisms of signal transduction elicited by this growth factor.

HGF-MET Signaling Shifts M1 Macrophages Toward an M2-Like Phenotype Through PI3K-Mediated Induction of Arginase-1 Expression.

Backgrounds and Aims: Hepatocyte Growth Factor (HGF)-MET signaling is known to promote biological functions such as cell survival, cell motility, and cell proliferation. However, it is unknown if HGF-MET alters the macrophage phenotype. In this study, we aimed to study the effects of HGF-MET signaling on the M1 macrophage phenotype. Methods and Materials: Bone marrow-derived macrophages (BMDMs) isolated from mice were either polarized to an M1 phenotype by IFN-γ and LPS treatment or to an M2 phenotype by IL-4 treatment. Changes in M1 or M2 markers induced by HGF-MET signaling were evaluated. Mechanisms responsible for alternations in the macrophage phenotype and intracellular metabolism were analyzed. Results: c-Met was expressed especially in M1 macrophages polarized by treatment with IFN-γ and LPS. In M1 macrophages, HGF-MET signaling induced the expression of Arg-1 mRNA and secretion of IL-10 and TGF-ß1 and downregulated the mRNA expression of iNOS, TNF-α, and IL-6. In addition, activation of the PI3K pathway and inactivation of NFκB were also observed in M1 macrophages treated with HGF. The increased Arg-1 expression and IL-10 secretion were abrogated by PI3K inhibition, whereas, no changes were observed in TNF-α and IL-6 expression. The inactivation of NFκB was found to be independent of the PI3K pathway. HGF-MET signaling shifted the M1 macrophages to an M2-like phenotype, mainly through PI3K-mediated induction of Arg-1 expression. Finally, HGF-MET signaling also shifted the M1 macrophage intracellular metabolism toward an M2 phenotype, especially with respect to fatty acid metabolism. Conclusion: Our results suggested that HGF treatment not only promotes regeneration in epithelial cells, but also leads to tissue repair by altering M1 macrophages to an M2-like phenotype.

Therapeutic Applications of Genes and Gene-Engineered Mesenchymal Stem Cells for Femoral Head Necrosis.

Osteonecrosis of the femoral head (ONFH) is a common and disabling joint disease. Although there is no clear consensus on the complex pathogenic mechanism of ONFH, trauma, abuse of glucocorticoids, and alcoholism are implicated in its etiology. The therapeutic strategies are still limited, and the clinical outcomes are not satisfactory. Mesenchymal stem cells (MSCs) have been shown to exert a positive impact on ONFH in preclinical experiments and clinical trials. The beneficial properties of MSCs are due, at least in part, to their ability to home to the injured tissue, secretion of paracrine signaling molecules, and multipotentiality. Nevertheless, the regenerative capacity of transplanted cells is impaired by the hostile environment of necrotic tissue in vivo, limiting their clinical efficacy. Recently, genetic engineering has been introduced as an attractive strategy to improve the regenerative properties of MSCs in the treatment of early-stage ONFH. This review summarizes the function of several genes used in the engineering of MSCs for the treatment of ONFH. Further, current challenges and future perspectives of genetic manipulation of MSCs are discussed. The notion of genetically engineered MSCs functioning as a "factory" that can produce a significant amount of multipotent and patient-specific therapeutic product is emphasized.

Angiocrine Hepatocyte Growth Factor Signaling Controls Physiological Organ and Body Size and Dynamic Hepatocyte Proliferation to Prevent Liver Damage during Regeneration.

Liver sinusoidal endothelial cells (LSECs) control organ functions, metabolism, and development through the secretion of angiokines. LSECs express hepatocyte growth factor (Hgf), which is involved in prenatal development, metabolic homeostasis, and liver regeneration. This study aimed to elucidate the precise contribution of LSEC-derived Hgf in physiological homeostasis and liver regeneration. Stab2-iCretg/wt;Hgffl/fl (HgfΔLSEC) mice were generated to abrogate Hgf expression selectively in LSECs from early fetal development onwards, to study global development, metabolic and endothelial zonation, and organ functions as well as liver regeneration in response to 70% partial hepatectomy (PH). Although zonation and liver/body weight ratios were not altered, total body weight and total liver weight were reduced in HgfΔLSEC. Necrotic organ damage was more marked in HgfΔLSEC mice, and regeneration was delayed 72 hours after PH. This was associated with decreased hepatocyte proliferation at 48 hours after PH. Molecularly, HgfΔLSEC mice showed down-regulation of Hgf/c-Met signaling and decreased expression of Deptor in hepatocytes. In vitro knockdown of Deptor was associated with decreased proliferation. Therefore, angiocrine Hgf controls hepatocyte proliferation and susceptibility to necrosis after partial hepatectomy via the Hgf/c-Met axis involving Deptor to prevent excessive organ damage.

The Role of MET in Melanoma and Melanocytic Lesions.

Melanoma is the leading cause of death due to cutaneous malignancy and its incidence is on the rise. Several signaling pathways, including receptor tyrosine kinases, have been recognized to have an etiopathogenetic role in the development and progression of precursor melanocytic lesions and malignant melanoma. Among those, the hepatocyte growth factor/MET (HGF/MET) axis is emerging as a critical player not only in the tumor itself but also in the immune microenvironment in which the tumor grows and advances in its development. Moreover, the activation of this pathway has emerged as a paradigm of tumor resistance to modern targeted therapies, and the assessment of its expression in patients' samples may be a valuable biomarker of tumor progression and response to targeted therapy. Here we summarize our current understanding of this important receptor tyrosine kinase in normal melanocyte proliferation/motility, in tumor progression and metastasis, its genetic alterations in certain subtype of melanocytic lesions, and how its pathway has been explored for the development of selective inhibitors.

Downregulation of lncRNA UCA1 facilitates apoptosis and reduces proliferation in multiple myeloma via regulation of the miR-1271-5p/HGF axis.

BACKGROUND: Long noncoding RNAs (lncRNAs) are considered to be a novel prognostic and therapeutic target in many cancers. This study identified dysregulation of lncRNA urothelial carcinoma associated 1 (UCA1) and hepatocyte growth factor (HGF) mRNA via the Gene Expression Omnibus (GEO) database, which was traced to the mutual target miRNA, miR-1271-5p, and their effects were explored in multiple myeloma (MM). METHODS: RNA expression profiles of MM were downloaded from the GEO database and analyzed using R packages. The expression of RNAs in MM tissue samples and cells was evaluated through quantificational real-time polymerase chain reaction (qRT-PCR). A luciferase reporter assay was utilized to confirm the binding relationships between UCA1/HGF and miR-1271-5p. To assess cell proliferation and apoptosis, CCK-8 assays and flow cytometry were conducted. Additionally, tumor progression was demonstrated in vivo. RESULTS: LncRNA UCA1 and HGF expression was higher in the cells and samples of patients with MM than in normal plasma cells. miR-1271-5p was confirmed to be the target of lncRNA UCA1 and HGF and to be negatively correlated with them. Moreover, downregulation of lncRNA UCA1 and HGF inhibited cell proliferation and facilitated cell apoptosis in RPMI 8226 cells (human MM cell line). However, miR-1271-5p overexpression affected the proliferation decrease and apoptosis increase. Moreover, in vivo experiments indicated that down or upregulation of lncRNA UCA1 repressed or enhanced the tumor growth of MM, respectively, in xenograft models. CONCLUSION: LncRNA UCA1 promoted proliferation and inhibited apoptosis by regulating miR-1271-5p and HGF in the human MM cell line RPMI 8226. Our investigations might contribute to a better understanding of the lncRNA UCA1/miR-1271-5p/HGF axis as a potential therapeutic strategy in MM.

M2 macrophages mediate sorafenib resistance by secreting HGF in a feed-forward manner in hepatocellular carcinoma.

BACKGROUND: Sorafenib is the only approved first line systemic therapy for advanced hepatocellular carcinoma (HCC) in the last decade. Tumour resistance to sorafenib has been of major obstacles to improve HCC patient survival. METHODS: We polarised THP-1 cells to M1 and M2 macrophages, performed various in vitro assays and developed sorafenib-resistant xenograft models to investigate the role of tumour-associated macrophages (TAM)-secreted molecules in HCC resistance to the targeted therapy. RESULTS: We demonstrated M2, but not M1, macrophages not only promote proliferation, colony formation and migration of hepatoma cells but also significantly confer tumour resistance to sorafenib via sustaining tumour growth and metastasis by secreting hepatocyte growth factor (HGF). HGF activates HGF/c-Met, ERK1/2/MAPK and PI3K/AKT pathways in tumour cells. Tumour-associated M2 macrophages were accumulated in sorafenib-resistance tumours more than in sorafenib-sensitive tumours in vivo and produced abundant HGF. HGF chemoattracts more macrophages migrated from surrounding area, regulates the distribution of M2 macrophages and increases hepatoma resistance to sorafenib in a feed-forward manner. CONCLUSIONS: Our results provide new insights into the mechanisms of sorafenib resistance in HCC and rationale for developing new trials by combining sorafenib with a potent HGF inhibitor such as cabozantinib to improve the first line systemic therapeutic efficacy.

IL-6 Trans-signaling Controls Liver Regeneration After Partial Hepatectomy.

Interleukin-6 (IL-6) is critically involved in liver regeneration after partial hepatectomy (PHX). Previous reports suggest that IL-6 trans-signaling through the soluble IL-6/IL-6R complex is involved in this process. However, the long-term contribution of IL-6 trans-signaling for liver regeneration after PHX is unknown. PHX-induced generation of the soluble IL-6R by ADAM (a disintegrin and metallo) proteases enables IL-6 trans-signaling, in which IL-6 forms an agonistic complex with the soluble IL-6 receptor (sIL-6R) to activate all cells expressing the signal-transducing receptor chain glycoprotein 130 (gp130). In contrast, without activation of ADAM proteases, IL-6 in complex with membrane-bound IL-6R and gp130 activates classic signaling. Here, we describe the generation of IL-6 trans-signaling mice, which exhibit boosted IL-6 trans-signaling and abrogated classic signaling by genetic conversion of all membrane-bound IL-6R into sIL-6R proteins phenocopying hyperactivation of ADAM-mediated shedding of IL-6R as single substrate. Importantly, although IL-6R deficient mice were strongly affected by PHX, survival and regeneration of IL-6 trans-signaling mice was indistinguishable from control mice, demonstrating that IL-6 trans-signaling fully compensates for disabled classic signaling in liver regeneration after PHX. Moreover, we monitored the long-term consequences of global IL-6 signaling inhibition versus IL-6 trans-signaling selective blockade after PHX by IL-6 monoclonal antibodies and soluble glycoprotein 130 as fragment crystallizable fusion, respectively. Both global IL-6 blockade and selective inhibition of IL-6 trans-signaling results in a strong decrease of overall survival after PHX, accompanied by decreased signal transducer and activator of transcription 3 phosphorylation and proliferation of hepatocytes. Mechanistically, IL-6 trans-signaling induces hepatocyte growth factor production by hepatic stellate cells. Conclusion: IL-6 trans-signaling, but not classic signaling, controls liver regeneration following PHX.

Proteolytic cleavages of MET: the divide-and-conquer strategy of a receptor tyrosine kinase.

Membrane-anchored full-length MET stimulated by its ligand HGF/SF induces various biological responses, including survival, growth, and invasion. This panel of responses, referred to invasive growth, is required for embryogenesis and tissue regeneration in adults. On the contrary, MET deregulation is associated with tumorigenesis in many kinds of cancer. In addition to its well-documented ligand-stimulated downstream signaling, the receptor can be cleaved by proteases such as secretases, caspases, and calpains. These cleavages are involved either in MET receptor inactivation or, more interestingly, in generating active fragments that can modify cell fate. For instance, MET fragments can promote cell death or invasion. Given a large number of proteases capable of cleaving MET, this receptor appears as a prototype of proteolytic-cleavage-regulated receptor tyrosine kinase. In this review, we describe and discuss the mechanisms and consequences, both physiological and pathological, of MET proteolytic cleavages. [BMB Reports 2019; 52(4): 239-249].

MST1 Suppression Reduces Early Brain Injury by Inhibiting the NF-κB/MMP-9 Pathway after Subarachnoid Hemorrhage in Mice.

BACKGROUND: Mammalian sterile 20-like kinase 1 (MST1), the key component of the Hippo-YAP pathway, exhibits an important role in the pathophysiological process of various neurological disorders, including ischemic stroke and spinal cord injury. However, during subarachnoid hemorrhage, the involvement of MST1 in the pathophysiology of early brain injury remains unknown. METHODS: We employed intravascular filament perforation to establish the subarachnoid hemorrhage (SAH) mouse model. The MST1 inhibitor XMU-MP-1 was intraperitoneally injected at 1 h after SAH, followed by daily injections. MST1 in vivo knockdown was performed 3 weeks prior to SAH via intracerebroventricular injection of adeno-associated virus (AAV) packaged with MST1 shRNA. The SAH grade, behavioral deficits, TUNEL staining, Evans blue dye extravasation and fluorescence, brain water content, protein and cytokine expressions by Western blotting, immunofluorescence, and proteome cytokine array were evaluated. RESULTS: Following SAH, the phosphorylation level of MST1 was upregulated at 12 h, with a peak at 72 h after SAH. It was colocalized with the microglial marker Iba1. Both XMU-MP-1 and MST1 shRNA alleviated the neurological deficits, blood-brain barrier (BBB) disruption, brain edema, neuroinflammation, and white matter injury, which were induced by SAH in association with nuclear factor- (NF-) κB p65 and matrix metallopeptidase-9 (MMP-9) activation and downregulated endothelial junction protein expression. CONCLUSIONS: The current findings indicate that MST1 participates in SAH-induced BBB disruption and white matter fiber damage via the downstream NF-κB-MMP-9 signaling pathway. Therefore, MST1 antagonists may serve as a novel therapeutic target to prevent early brain injury in SAH patients.

Hepatocyte growth factor acts as a mitogen for equine satellite cells via protein kinase C δ-directed signaling.

Hepatocyte growth factor (HGF) signals mediate mouse skeletal muscle stem cell, or satellite cell (SC), reentry into the cell cycle and myoblast proliferation. Because the athletic horse experiences exercise-induced muscle damage, the objective of the experiment was to determine the effect of HGF on equine SC (eqSC) bioactivity. Fresh isolates of adult eqSC were incubated with increasing concentrations of HGF and the initial time to DNA synthesis was measured. Media supplementation with HGF did not shorten (P > 0.05) the duration of G0/G1 transition suggesting the growth factor does not affect activation. Treatment with 25 ng/mL HGF increased (P < 0.05) eqSC proliferation that was coincident with phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and AKT serine/threonine kinase 1 (AKT1). Chemical inhibition of the upstream effectors of ERK1/2 or AKT1 elicited no effect (P > 0.05) on HGF-mediated 5-ethynyl-2'-deoxyuridine (EdU) incorporation. By contrast, treatment of eqSC with 2 µm Gö6983, a pan-protein kinase C (PKC) inhibitor, blocked (P < 0.05) HGF-initiated mitotic activity. Gene-expression analysis revealed that eqSC express PKCα, PKCδ, and PKCε isoforms. Knockdown of PKCδ with a small interfering RNA (siRNA) prevented (P > 0.05) HGF-mediated EdU incorporation. The siPKCδ was specific to the kinase and did not affect (P > 0.05) expression of either PKCα or PKCε. Treatment of confluent eqSC with 25 ng/mL HGF suppressed (P < 0.05) nuclear myogenin expression during the early stages of differentiation. These results demonstrate that HGF may not affect activation but can act as a mitogen and modest suppressor of differentiation.

Hepatocyte Growth Factor (HGF) Promotes Peripheral Nerve Regeneration by Activating Repair Schwann Cells.

During the peripheral nerve regeneration process, a variety of neurotrophic factors play roles in nerve repair by acting on neuronal or non-neuronal cells. In this report, we investigated the role(s) of hepatocyte growth factor (HGF) and its receptor, c-met, in peripheral nerve regeneration. When mice were subjected to sciatic nerve injury, the HGF protein level was highly increased at the injured and distal sites. The level of both total and phosphorylated c-met was also highly upregulated, but almost exclusively in Schwann cells (SCs) distal from the injury site. When mice were treated with a c-met inhibitor, PHA-665752, myelin thickness and axon regrowth were decreased indicating that re-myelination was hindered. HGF promoted the migration and proliferation of cultured SCs, and also induced the expression of various genes such as GDNF and LIF, presumably by activating ERK pathways. Furthermore, exogenous supply of HGF around the injury site, by intramuscular injection of a plasmid DNA expressing human HGF, enhanced the myelin thickness and axon diameter in injured nerves. Taken together, our results indicate that HGF and c-met play important roles in Schwann cell-mediated nerve repair, and also that HGF gene transfer may provide a useful tool for treating peripheral neuropathy.

The Impact of the Epithelial-Mesenchymal Transition Regulator Hepatocyte Growth Factor Receptor/Met on Skin Immunity by Modulating Langerhans Cell Migration.

Langerhans cells (LCs), the epidermal dendritic cell (DC) subset, express the transmembrane tyrosine kinase receptor Met also known as hepatocyte growth factor (HGF) receptor. HGF is the exclusive ligand of Met and upon binding executes mitogenic, morphogenic, and motogenic activities to various cells. HGF exerts anti-inflammatory activities via Met signaling and was found to regulate various functions of immune cells, including differentiation and maturation, cytokine production, cellular migration and adhesion, and T cell effector function. It has only recently become evident that a number of HGF-regulated functions in inflammatory processes and immune responses are imparted via DCs. However, the mechanisms by which Met signaling in DCs conveys its immunoregulatory effects have not yet been fully understood. In this review, we focus on the current knowledge of Met signaling in DCs with particular attention on the morphogenic and motogenic activities. Met signaling was shown to promote DC mobility by regulating matrix metalloproteinase activities and adhesion. This is a striking resemblance to the role of Met in regulating a cell fate program during embryonic development, wound healing, and in tumor invasion known as epithelial-mesenchymal transition (EMT). Hence, we propose the concept that an EMT program is executed by Met signaling in LCs.

MST1 down-regulation in decreasing apoptosis of aortic dissection smooth muscle cell apoptosis.

OBJECTIVE: Elevated apoptosis of vascular smooth muscle cell (VSMC) is correlated with the occurrence of aortic dissection (AD). Mammalian ste20-like protein kinase 1 (MST1) is one important component of Hippo-YAP signal pathway for activation and cell apoptosis facilitation. Whether MST1 plays a role in AD pathogenesis is unclear yet. This study established an AD rat model to investigate the role of MST1 in regulating VSMC apoptosis and AD pathogenesis. MATERIALS AND METHODS: Cell apoptosis was compared between AD vascular tissues and normal rats, in addition to Caspase-3 activity, and expression of MST1, p-LATS1, p-YAP1, YAP1. In vitro cultured VSMCs from AD rats were treated with siRNA-MST1 to test apoptotic rate and Caspase-3 activity. AD model rats were treated with pGLVU6/GFP-MST1 for comparing MST1, p-LATS1, p-YAP1, and YAP1 expression, along with Caspase-3 activity, cell apoptosis, AD formation rate, diameter, and length. RESULTS: Compared to control group, AD rats had elevated vascular cell apoptosis, Caspase-3 activity, expressions of MST1, p-LATS1, and p-YAP1, plus lower YAP1 expression. siRNA interference of MST1 significantly inhibited apoptosis of in vitro cultured VSMC. shRNA lentivirus targeting MST1 pGLVU6/GFP-MST1 remarkably decreased expression of MST1, p-LATS1, and p-YAP1 in AD rat vascular tissues, increased YAP1 expression, decreased VSMC apoptosis, AD formation rate, AD diameter/length. CONCLUSIONS: MST1 up-regulation plays a role in facilitating VSMC apoptosis and AD pathogenesis. Down-regulation of MST1 decreased VSMC apoptosis and AD formation.