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Heme oxygenase-1 (HO-1) has been implicated in tumor progression, but the underlying molecular mechanisms remain largely unknown. Transforming growth factor-β1 (TGF-β1) 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-β1-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) 3 Cl 2 ] 2 , suggesting an inhibitory role of the HO-1/CO axis in TGF-β signaling to growth inhibition in HCC cell lines. Interestingly, we observed that [Ru(CO) 3 Cl 2 ] 2 inhibits TGF-β1-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) 3 Cl 2 ] 2 on cell cycle arrest induced by TGF-β1. These findings for the first time demonstrate that HO-1/CO axis confer resistance of HCC cells to TGF-β growth inhibitory signal by increasing Smad3 phosphorylation at Thr-179 via ERK1/2 pathway. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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-β1 (TGF-β1)-induced cell cycle arrest. In human MCF10A mammary epithelial cells, TGF-β1 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-β1-induced p27KIP1 expression and cell cycle arrest. TGF-β1 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-β1-dependent manner. These results for the first time demonstrate a role of Cdk5/p35 in the regulation of cell cycle progression modulated by TGF-β1. [ABSTRACT FROM AUTHOR]

Highlights: [•] H2O2 inhibits TGF-β1-induced cell cycle arrest. [•] H2O2 induces Smad3 linker phosphorylation through Akt-ERK1/2 pathway. [•] H2O2-mediated suppression of TGF-β signal requires Smad3 linker phosphorylation. [•] This is a first report about interplay between H2O2 and growth inhibition pathway. [ABSTRACT FROM AUTHOR]

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-β1 (TGF-β1) response. We found that LTB4 pretreatment or ectopic expression of BLT1, a high affinity LTB4 receptor, fully abrogated TGF-β1-induced cell cycle arrest and expression of p15INK4B and p27KIP1. Mechanism study revealed that LTB4-mediated suppression of TGF-β1-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-β1-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-β1, providing a novel mechanistic insight into the connection between enhanced inflammatory signal and cancer cell growth.