Heme oxygenase-1/carbon monoxide axis suppresses transforming growth factor-ß1-induced growth inhibition by increasing ERK1/2-mediated phosphorylation of Smad3 at Thr-179 in human hepatocellular carcinoma cell lines.

Heme oxygenase-1 (HO-1) has been implicated in tumor progression, but the underlying molecular mechanisms remain largely unknown. Transforming growth factor-ß1 (TGF-ß1) exhibits cytostatic and apoptotic effects in hepatocytes and several types of hepatocellular carcinoma (HCC) cell lines, and deregulation of its signaling pathway is linked to hepatic tumorigenesis. In the present study, we observed that HO-1 is expressed at higher levels in HCC tissues than in paired normal tissues. Moreover, TGF-ß1-induced cell cycle arrest and up-regulation of cyclin-dependent kinase inhibitors in HCC cell lines were significantly attenuated by overexpression of HO-1 or treatment with tricarbonyldichlororuthenium(II) dimer ([Ru(CO)3Cl2]2, suggesting an inhibitory role of the HO-1/CO axis in TGF-ß signaling to growth inhibition in HCC cell lines. Interestingly, we observed that [Ru(CO)3Cl2]2 inhibits TGF-ß1-induced Smad3-dependent reporter activity without affecting its C-terminus phosphorylation, complex formation with Smad4, and nuclear translocation. Additional experiments revealed that HO-1/CO axis selectively induces phosphorylation of Smad3 at Thr-179 residue in the linker region through activation of extracellular signal-activated kinase (ERK) 1/2. Transfection with a phospho-deficient Smad3 (T179A) mutant or treatment with FR180204, a specific inhibitor for ERK1/2, significantly reversed the inhibitory effects of HO-1 and [Ru(CO)3Cl2]2 on cell cycle arrest induced by TGF-ß1. These findings for the first time demonstrate that HO-1/CO axis confer resistance of HCC cells to TGF-ß growth inhibitory signal by increasing Smad3 phosphorylation at Thr-179 via ERK1/2 pathway.

Programed Assembly of Nucleoprotein Nanoparticles Using DNA and Zinc Fingers for Targeted Protein Delivery.

With a growing number of intracellular drug targets and the high efficacy of protein therapeutics, the targeted delivery of active proteins with negligible toxicity is a challenging issue in the field of precision medicine. Herein, a programed assembly of nucleoprotein nanoparticles (NNPs) using DNA and zinc fingers (ZnFs) for targeted protein delivery is presented. Two types of ZnFs with different sequence specificities are genetically fused to a targeting moiety and a protein cargo, respectively. Double-stranded DNA with multiple ZnF-binding sequences is grafted onto inorganic nanoparticles, followed by conjugation with the ZnF-fused proteins, generating the assembly of NNPs with a uniform size distribution and high stability. The approach enables controlled loading of a protein cargo on the NNPs, offering a high cytosolic delivery efficiency and target specificity. The utility and potential of the assembly as a versatile protein delivery vehicle is demonstrated based on their remarkable antitumor activity and target specificity with negligible toxicity in a xenograft mice model.

Transforming growth factor-ß1 induces cell cycle arrest by activating atypical cyclin-dependent kinase 5 through up-regulation of Smad3-dependent p35 expression in human MCF10A mammary epithelial cells.

Cyclin-dependent kinases (Cdks) play important roles in control of cell division. Cdk5 is an atypical member of Cdk family with non-cyclin-like regulatory subunit, p35, but its role in cell cycle progression is still unclear. In the present study, we investigated the role of Cdk5/p35 on transforming growth factor-ß1 (TGF-ß1)-induced cell cycle arrest. In human MCF10A mammary epithelial cells, TGF-ß1 induced cell cycle arrest at G1 phase and increased p27KIP1 expression. Interestingly, pretreatment with roscovitine, an inhibitor of Cdk5, or transfection with small interfering (si) RNAs specific to Cdk5 and p35 significantly attenuated the TGF-ß1-induced p27KIP1 expression and cell cycle arrest. TGF-ß1 increased Cdk5 activity via up-regulation of p35 gene at transcriptional level, and these effects were abolished by transfection with Smad3 siRNA or infection of adenovirus carrying Smad3 mutant at the C-tail (3SA). Chromatin immunoprecipitation assay further revealed that wild type Smad3, but not mutant Smad3 (3SA), binds to the region of the p35 promoter region (-1000--755) in a TGF-ß1-dependent manner. These results for the first time demonstrate a role of Cdk5/p35 in the regulation of cell cycle progression modulated by TGF-ß1.

Hydrogen peroxide inhibits transforming growth factor-ß1-induced cell cycle arrest by promoting Smad3 linker phosphorylation through activation of Akt-ERK1/2-linked signaling pathway.

Hydrogen peroxide (H2O2) functions as a second messenger in growth factor receptor-mediated intracellular signaling cascade and is tumorigenic by virtue of its ability to promote cell proliferation; however, the mechanisms underlying the growth stimulatory action of H2O2 are less understood. Here we report an important mechanism for antagonistic effects of H2O2 on growth inhibitory response to transforming growth factor-ß1 (TGF-ß1). In Mv1Lu and HepG2 cells, pretreatment of H2O2 (0.05-0.2 mM) completely blocked TGF-ß1-mediated induction of p15(INK4B) expression and increase of its promoter activity. Interestingly, H2O2 selectively suppressed the transcriptional activation potential of Smad3, not Smad2, in the absence of effects on TGF-ß1-induced phosphorylation of the COOH-tail SSXS motif of Smad3 and its nuclear translocation. Mechanism studies showed that H2O2 increases the phosphorylation of Smad3 at the middle linker region in a concentration- and time-dependent manner and this effect is mediated by activation of extracellular signal-activated kinase 1/2 through Akt. Furthermore, expression of a mutant Smad3 in which linker phosphorylation sites were ablated significantly abrogated the inhibitory effects of H2O2 on TGF-ß1-induced increase of p15(INK4B)-Luc reporter activity and blockade of cell cycle progression from G1 to S phase. These findings for the first time define H2O2 as a signaling molecule that modulate Smad3 linker phosphorylation and its transcriptional activity, thus providing a potential mechanism whereby H2O2 antagonizes the cytostatic function of TGF-ß1.

n-Propyl gallate suppresses lipopolysaccharide-induced inducible nitric oxide synthase activation through protein kinase Cδ-mediated up-regulation of heme oxygenase-1 in RAW264.7 macrophages.

n-Propyl gallate is a synthetic phenolic antioxidant with potential anti-inflammatory effects. However, the underlying mechanism remains largely unknown. In the present study, we showed that n-propyl gallate increases the expression and activity of the heme oxygenase-1 (HO-1), a stress-inducible protein with potent anti-inflammatory activity, in RAW264.7 macrophages. The inhibition of the HO-1 activity by treatment with zinc (II) protoporphyrin IX (ZnPP) or by knockdown of the HO-1 expression with small interference RNA significantly reversed the inhibitory effect of n-Propyl gallate on activations of nuclear factor-κB (NF-κB) and inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide (LPS). An additional mechanism study using inhibitors of signaling kinases revealed the involvement of protein kinase Cδ (PKCδ) in the expression of HO-1 induced by n-Propyl gallate. Consistent with these results, n-Propyl gallate increased the intracellular levels of phosphorylated PKCδ in concentration- and time-dependent manners. The inhibitory effects of n-Propyl gallate on LPS-induced iNOS expression and nitric oxide production were also significantly attenuated by pretreatment with the PKCδ inhibitor, rottlerin, or by transfection with PKCδ (K376R), a kinase-inactive form of PKCδ. Taken together, these findings provide the first evidence that n-Propyl gallate exerts its anti-inflammatory effect through PKCδ-mediated up-regulation of HO-1 in macrophages.

Propyl gallate sensitizes human lung cancer cells to cisplatin-induced apoptosis by targeting heme oxygenase-1 for TRC8-mediated degradation.

Heme oxygenase-1 (HO-1) significantly contributes to survival of cancer cells and is being considered as one of therapeutic targets for cancer treatment. Propyl gallate (PG) is a synthetic phenolic compound that possess a potent anti-oxidant and anti-inflammatory activities. In the present study, we investigated whether PG exhibit an anti-cancer effect through modulating HO-1 activation. In human non-small cell lung cancer (NSCLC) cells, treatment with PG dose-dependently diminished HO-1 protein levels without changing its mRNA levels and consequently decreased HO-1 activity. PG also significantly enhanced the sensitivity of NSCLC cells to cisplatin-induced apoptosis, and this effect was attenuated by overexpression of HO-1. Mechanistically, PG exerted its chemosensitization effect by down-regulating HO-1 protein expression through a TRC8 (translocation in renal carcinoma, chromosome 8)-mediated ubiquitin-proteasome pathway. Collectively, our data provide the potential application of PG in combination chemotherapy to enhance drug sensitivity in lung cancer by targeting HO-1.

BIX02189 inhibits TGF-ß1-induced lung cancer cell metastasis by directly targeting TGF-ß type I receptor.

Transforming growth factor-ß1 (TGF-ß1) promotes tumor metastasis by inducing an epithelial-to-mesenchymal transition (EMT) in cancer cells. In this study, we investigated the effects of BIX02189 and XMD8-92, pharmacologic inhibitors of the MEK5 [mitogen-activated protein kinase/extracellular-signal-regulated kinase (ERK)5] signaling pathway, on the EMT and migration of cancer cells induced by TGF-ß1. In human A549 lung cancer cells, TGF-ß1-induced EMT, cell motility, and expression of matrix metalloproteinase-2 were completely inhibited by BIX02189, but not by XMD8-92 or small interference RNAs specific to MEK5 and ERK5. Interestingly, BIX02189 strongly blocked the activation of TGF-ß1 signaling components, and this inhibitory effect was not reproduced by MEK5 inhibition. Molecular docking simulation and kinase assays revealed that BIX02189 binds directly to the ATP-binding site of the TGF-ß receptor type I (TßRI) and suppresses its kinase activity. Finally, the anti-metastatic effect of BIX02189 was validated in a TßRI-derived A549 xenograft mouse model. Collectively, these findings newly characterize BIX02189 as a potent inhibitor of TßRI that can block the tumor metastatic activity of TGF-ß1.

Kaempferol Suppresses Transforming Growth Factor-ß1-Induced Epithelial-to-Mesenchymal Transition and Migration of A549 Lung Cancer Cells by Inhibiting Akt1-Mediated Phosphorylation of Smad3 at Threonine-179.

Kaempferol, a natural dietary flavonoid, is well known to possess chemopreventive and therapeutic anticancer efficacy; however, its antimetastatic effects have not been mechanistically studied so far in any cancer model. This study was aimed to investigate the inhibitory effect and accompanying mechanisms of kaempferol on epithelial-to-mesenchymal transition (EMT) and cell migration induced by transforming growth factor-ß1 (TGF-ß1). In human A549 non-small lung cancer cells, kaempferol strongly blocked the enhancement of cell migration by TGF-ß1-induced EMT through recovering the loss of E-cadherin and suppressing the induction of mesenchymal markers as well as the upregulation of TGF-ß1-mediated matrix metalloproteinase-2 activity. Interestingly, kaempferol reversed TGF-ß1-mediated Snail induction and E-cadherin repression by weakening Smad3 binding to the Snail promoter without affecting its C-terminus phosphorylation, complex formation with Smad4, and nuclear translocation under TGF-ß1 stimulation. Mechanism study revealed that the phosphorylation of Smad3 linker region induced by TGF-ß1 was required for the induction of EMT and cell migration, and selective downregulation of the phosphorylation of Smad3 at Thr179 residue (not Ser204, Ser208, and Ser213) in the linker region was responsible for the inhibition by kaempferol of TGF-ß1-induced EMT and cell migration. Furthermore, Akt1 was required for TGF-ß1-mediated induction of EMT and cell migration and directly phosphorylated Smad3 at Thr179, and kaempferol completely abolished TGF-ß1-induced Akt1 phosphorylation. In summary, kaempferol blocks TGF-ß1-induced EMT and migration of lung cancer cells by inhibiting Akt1-mediated phosphorylation of Smad3 at Thr179 residue, providing the first evidence of a molecular mechanism for the anticancer effect of kaempferol.

The proinflammatory LTB4/BLT1 signal axis confers resistance to TGF-ß1-induced growth inhibition by targeting Smad3 linker region.

Leukotriene B4 (LTB4) is a potent pro-inflammatory eicosanoid that is derived from arachidonic acid, and its signaling is known to have a tumor-promoting role in several cancer types. In this study, we investigated whether enhanced LTB4 signaling confers resistance to the cytostatic transforming growth factor-ß1 (TGF-ß1) response. We found that LTB4 pretreatment or ectopic expression of BLT1, a high affinity LTB4 receptor, fully abrogated TGF-ß1-induced cell cycle arrest and expression of p15INK4B and p27KIP1. Mechanism study revealed that LTB4-mediated suppression of TGF-ß1-induced Smad3 activation and growth inhibition was due to enhanced phosphorylation of Smad3 linker region (pSmad3L) through activation of BLT1-NAD(P)H oxidase (NOX)-reactive oxygen species (ROS)-epidermal growth factor receptor (EGFR)-phosphatidylinositol 3-kinase (PI3-K)-extracellular signal-activated kinase1/2 (ERK1/2)-linked signaling cascade. Furthermore, the LTB4/BLT1 signaling pathway leading to pSmad3L was constitutively activated in breast cancer cells and was correlated with TGF-ß1-resistant growth of the cells in vitro and in vivo. In human breast cancer tissues, the expression level of pSmad3L (Thr179) had a positive correlation with BLT1 expression. Collectively, our data demonstrate for the first time that the induction of pSmad3L through BLT1-NOX-ROS-EGFR-PI3K-ERK1/2 signaling pathway is a key mechanism by which LTB4 blocks the anti-proliferative responses of TGF-ß1, providing a novel mechanistic insight into the connection between enhanced inflammatory signal and cancer cell growth.