PKC-MEK-MAPK-dependent signal transduction pathway mediates the stimulation of lysyl oxidase expression by serum and PDGF in rat aortic smooth muscle cells

Molecular Cues Guiding Matrix Stiffness in Liver Fibrosis

Tissue and matrix stiffness affect cell properties during morphogenesis, cell growth, differentiation, and migration and are altered in the tissue remodeling following injury and the pathological progression. However, detailed molecular mechanisms underlying alterations of stiffness in vivo are still poorly understood. Recent engineering technologies have developed powerful techniques to characterize the mechanical properties of cell and matrix at nanoscale levels. Extracellular matrix (ECM) influences mechanical tension and activation of pathogenic signaling during the development of chronic fibrotic diseases. In this short review, we will focus on the present knowledge of the mechanisms of how ECM stiffness is regulated during the development of liver fibrosis and the molecules involved in ECM stiffness as a potential therapeutic target for liver fibrosis.

IL-1β-Induced Mesenchymal Stem Cell Migration Involves MLCK Activation via PKC Signaling

Mesenchymal stem cells (MSCs) migrate via the bloodstream to sites of injury, possibly attracted by inflammatory cytokines. Although many cytokines can induce stem cell migration, the underlying mechanism is not fully understood. We found that tail vein-injected MSCs migrate to the pancreas in nonobese diabetic (NOD) mice. An ELISA assay revealed that hyperglycemic NOD mice have higher pancreatic levels of interleukin-1β (IL-1β) than normal NOD mice and that IL-1β stimulates MSC migration in a Transwell assay and electric cell-substrate impedance sensing system. Microarray analysis showed that myosin light chain kinase (MLCK) is involved in IL-1β-induced MSC migration, while Western blots showed that IL-1β stimulates MLCK expression and activation and that MLCK-siRNA transfection reduces MSC migration. Kinase inhibitors, chromatin immunoprecipitation, and a knockdown study revealed that IL-1β-induced MLCK expression is regulated by the PKCδ/NF-κB signaling pathway, and a kinase inhibitor study revealed that IL-1β-induced MLCK activation occurs via the PKCα/MEK/ERK signaling pathway. These results show that IL-1β released from the pancreas of hyperglycemic NOD mice induces MSC migration and that this is dependent on MLCK expression via the PKCδ/NF-κB pathway and on MLCK activation via the PKCα/MEK/ERK signaling cascade. This study increases our understanding of the mechanisms by which MSCs home to injury sites.

Transforming growth factor alpha is a critical mediator of radiation lung injury

Radiation fibrosis of the lung is a late toxicity of thoracic irradiation. Epidermal growth factor (EGF) signaling has previously been implicated in radiation lung injury. We hypothesized that TGF-α, an EGF receptor ligand, plays a key role in radiation-induced fibrosis in lung. Mice deficient in transforming growth factor (TGF-α(-/-)) and control C57Bl/6J (C57-WT) mice were exposed to thoracic irradiation in 5 daily fractions of 6 Gy. Cohorts of mice were followed for survival (n ≥ 5 per group) and tissue collection (n = 3 per strain and time point). Collagen accumulation in irradiated lungs was assessed by Masson's trichrome staining and analysis of hydroxyproline content. Cytokine levels in lung tissue were assessed with ELISA. The effects of TGF-α on pneumocyte and fibroblast proliferation and collagen production were analyzed in vitro. Lysyl oxidase (LOX) expression and activity were measured in vitro and in vivo. Irradiated C57-WT mice had a median survival of 24.4 weeks compared to 48.2 weeks for irradiated TGF-α(-/-) mice (P = 0.001). At 20 weeks after irradiation, hydroxyproline content was markedly increased in C57-WT mice exposed to radiation compared to TGF-α(-/-) mice exposed to radiation or unirradiated C57-WT mice (63.0, 30.5 and 37.6 μg/lung, respectively, P = 0.01). C57-WT mice exposed to radiation had dense foci of subpleural fibrosis at 20 weeks after exposure, whereas the lungs of irradiated TGF-α (-/-) mice were largely devoid of fibrotic foci. Lung tissue concentrations of IL-1β, IL-4, TNF-α, TGF-β and EGF at multiple time points after irradiation were similar in C57-WT and TGF-α(-/-) mice. TGF-α in lung tissue of C57-WT mice rose rapidly after irradiation and remained elevated through 20 weeks. TGF-α(-/-) mice had lower basal LOX expression than C57-WT mice. Both LOX expression and LOX activity were increased after irradiation in all mice but to a lesser degree in TGF-α(-/-) mice. Treatment of NIH-3T3 fibroblasts with TGF-α resulted in increases in proliferation, collagen production and LOX activity. These studies identify TGF-α as a critical mediator of radiation-induced lung injury and a novel therapeutic target in this setting. Further, these data implicate TGF-α as a mediator of collagen maturation through a TGF-β independent activation of lysyl oxidase.

Inhibitory effects of cilostazol on proliferation of vascular smooth muscle cells (VSMCs) through suppression of the ERK1/2 pathway

AIM

The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenic factor of vascular disorders such as atherosclerosis and restenosis after angioplasty. During atherogenesis or in response to vessel injury, VSMC proliferation is induced by a number of peptide growth factors released from platelets and VSMCs. Cilostazol is a phosphodiesterase (PDE) 3 inhibitor that increases intracellular cAMP levels and decreases intracellular Ca(2+) levels, inhibiting platelet aggregation and inducing vasodilatation. Cilostazol is also known to have an inhibitory effect on the proliferation of VSMCs, but the anti-proliferative mechanism of cilostazol in VSMCs has not yet been established. In the present study, we investigated whether the anti-proliferative mechanism of cilostazol is associated with the suppression of extracellular signal-regulated kinases (ERK) and phosphatidylinositol 3 kinase (PI3K) signaling pathways.

METHODS

To confirm the anti-proliferative effects of cilostazol on VSMCs, VSMCs were induced to proliferate by serum-induced mitogenesis and then were treated with cilostazol for 24 h. And, to investigate whether the anti-proliferative mechanism of cilostazol in VSMCs involves the suppression of the ERK and PI3K pathways, expression of the phosphorylated forms of ERK1/2, Raf, Akt, and glycogen synthase kinase (GSK)-3 were evaluated by western blot.

RESULTS

Cilostazol inhibited VSMC proliferation in a dose-dependent manner. Phosphorylated ERK1/2 and Raf were significantly reduced in a dose-dependent manner, whereas phosphorylated Akt and GSK-3 were not changed.

CONCLUSION

These results suggest that suppression of the ERK pathway but not the PI3K pathway is an important mechanism in the anti-proliferative effect of cilostazol on VSMCs.

Stem cell-derived Sca-1+ progenitors differentiate into smooth muscle cells, which is mediated by collagen IV-integrin alpha1/beta1/alphav and PDGF receptor pathways

Embryonic stem (ES) cells can differentiate into smooth muscle cells (SMCs) that can be used for tissue engineering and repair of damaged organs. However, little is known about the molecular mechanisms of differentiation in these cells. In the present study, we found collagen IV can promote ES cells to differentiate into stem cell antigen-1-positive (Sca-1(+)) progenitor cells and SMCs. Pretreatment of ES cells with antibodies against collagen IV significantly inhibited SMC marker expression. To further elucidate the effect of collagen IV on the induction and maintenance of SMC differentiation, Sca-1(+) progenitor cells were isolated with magnetic beads, placed in collagen-IV-coated flasks, and cultured in differentiation medium with or without platelet-derived growth factor (PDGF)-BB for 6-90 days. Both immunostaining and fluorescence-activated cell sorter analyses revealed that the majority of these cells were positive for SMC-specific markers. Pretreatment of Sca-1(+) progenitors with antibodies against integrin alpha(1), alpha(v), and beta(1), but not beta(3), inhibited focal adhesion kinase (FAK) and paxillin phosphorylation and resulted in a marked inhibition of SMC differentiation. Various tyrosine kinase inhibitors, and specific siRNA for phosphatidylinositol 3-kinase (PI 3-kinase) and PDGF receptor-beta significantly inhibited SMC marker expression. Taken together, we demonstrate for the first time that collagen IV plays a crucial role in the early stage of SMC differentiation and that integrin (alpha(1), beta(1), and alpha(v))-FAK-PI 3-kinase-mitogen-activated protein kinase and PDGF receptor-beta signaling pathways are involved in SMC differentiation.

PKCδ Is Necessary for Smad3 Expression and Transforming Growth Factor β–Induced Fibronectin Synthesis in Vascular Smooth Muscle Cells

Objective— The purpose of these studies is to investigate the mechanism by which transforming growth factor (TGF)β1 regulates the synthesis of the extracellular matrix protein fibronectin (FN).

Methods and Results— TGFβ1 elicited a time-dependent induction of FN protein and mRNA in A10 rat aortic smooth muscle cells (SMCs). Ectopic expression of Smad3 in A10 cells stimulated both basal and TGFβ1-induced FN expression, whereas expression of Smad7 eliminated the TGFβ response. Because TGFβ activated PKCδ in SMCs, we tested the role of PKCδ in regulation of FN expression. Inhibition of PKCδ activity by rottlerin or dominant-negative adenovirus (AdPKCδ DN) blocked TGFβ1’s induction of FN, whereas overexpression of PKCδ enhanced TGFβ’s effect. Moreover, aortic SMCs isolated from PKCδ −/− mice exhibited diminished FN induction in response to TGFβ. Furthermore, we found that Smad3 protein and mRNA were markedly reduced in AdPKCδ DN-treated A10 cells and in PKCδ null cells. Finally, restoring Smad3 in rottlerin-treated A10 and PKCδ null cells rescues the ability of TGFβ to upregulate FN protein and mRNA expression.

Conclusion— Our data suggest that TGFβ-activated PKCδ is critical to maintain normal expression of Smad3, which in turn is required for the induction of fibronectin. PKCδ represents a promising target for treating the fibroproliferative response after arterial injury.

Inhibitory effects of tetrandrine on the serum- and platelet-derived growth factor-BB-induced proliferation of rat aortic smooth muscle cells through inhibition of cell cycle progression, DNA synthesis, ERK1/2 activation and c-fos expression

Tetrandrine (TET) is a well known naturally occurred nonspecific Ca(2+) channel blocker. It has long been used for the treatment of arrhythmia, hypertension, and occlusive cardiovascular disorders. The objective of the present study was to investigate the effect of TET on the proliferation of primary cultured rat aortic smooth muscle cells (RASMCs). TET significantly inhibited both 10% fetal bovine serum (FBS) and 50 ng/ml platelet-derived growth factor (PDGF)-BB-induced proliferation, [(3) H] ]thymidine incorporation into DNA, and p42/p44 mitogen-activated protein kinase (ERK1/2) phosphorylation at the concentration of 1.0 and 5.0 microM. Flow cytometry analysis of DNA content in synchronized cells revealed blocking of the FBS-inducible cell cycle progression by TET. In accordance with these findings, TET 5 microM caused a 48% decrease in the early elevation of c-fos expression induced after 10% FBS addition. Furthermore, in contrast to its distinguishable higher potency of Ca(2+) antagonistic activity, verapamil showed lower potent antiproliferative activities than TET. These results suggest that TET can exert antiproliferative effects against mitogenic stimuli for RASMCs in vitro by a mechanism that involves the MAPK pathway, altering cell cycle progression, and the inhibitory action cannot be limited to its Ca(2+) modulation.

Lysyl oxidase inhibits ras-mediated transformation by preventing activation of NF-kappa B

Lysyl oxidase (LO), which catalyzes the oxidation of lysine residues, was previously shown to have anti-oncogenic activity on ras-transformed cells. Since oncogenic Ras mediates transformation, in part, through the activation of the transcription factor nuclear factor-kappa B (NF-kappa B), we tested here the effects of LO on NF-kappa B activity. Expression of LO in ras-transformed NIH 3T3 cells led to decreased NF-kappa B binding and activity, as well as the expression of the NF-kappa B target gene c-myc. Importantly, ectopic expression of LO led to a dramatic decrease in colony formation by ras-transformed NIH 3T3 cells, a finding comparable to the expression of the I kappa B alpha dominant-negative mutant, which could be rescued by p65/p50 NF-kappa B subunit expression. LO was unable to directly inhibit the activity of ectopically expressed p65 and c-Rel NF-kappa B subunits, suggesting that LO affected an upstream signaling pathway(s) induced by Ras. Consistent with this hypothesis, LO expression decreased both the rate of I kappa B alpha turnover and the activities of IKK alpha and IKK beta. Moreover, the ectopic expression of a constitutively active version of either kinase reversed the negative effects of LO. Ras can induce NF-kappa B via both the phosphatidylinositol 3-kinase (PI3K)/Akt and Raf/MEK pathways. LO potently downregulated the PI3K and Akt kinases, while partially inhibiting MEK kinase activity. Expression of a constitutively activated, myristylated Akt or PDK1 was able to counteract the effect of LO on NF-kappa B, whereas constitutively activated Raf was only partially effective. Importantly, LO blocked membrane localization of Akt and PDK1 in Ras-transformed cells. Overall, these results strongly argue that the anti-oncogenic effects of LO on ras-mediated transformation are due to its ability to inhibit signaling pathways that lead to activation of NF-kappa B.