Stathmin, a major microtubule-depolymerizing protein, is involved in cell cycle progression and cell motility. This study aimed to elucidate its role in the progression, early tumour recurrence (ETR), and prognosis of hepatocellular carcinoma (HCC). Stathmin mRNA was overexpressed in 88/156 (56%) resected, unifocal, primary HCCs, while p53 mutation was present in 72 (46%) and osteopontin mRNA overexpression in 79 (51%). Stathmin mRNA expression exhibited high concordance (93%) with protein expression in 107 cases examined by immunohistochemistry. Stathmin overexpression correlated with high alpha-fetoprotein (>200 ng/ml, p = 0.02), larger tumour size (>5 cm, p = 0.012), high tumour grade (p < 0.0002), high tumour stage (stage IIIA-IV) with vascular invasion and various degrees of intrahepatic metastasis (p < 1 x 10(-8)), ETR (p = 0.003), and lower 5-year survival (p = 0.0007). Stathmin protein expression was often more intense in the peripheral regions of tumour trabeculae, tumour borders, and portal vein tumour thrombi. Stathmin overexpression correlated with p53 mutation (p = 0.017) and osteopontin overexpression (p = 1 x 10(-8)), both of which were associated with vascular invasion (both p < 0.0001) and poorer prognosis (p < 0.0004 and p = 0.0004, respectively). Regardless of the status of p53 mutation or osteopontin expression, stathmin overexpression was associated with higher vascular invasion (all p < 0.0001). Approximately 90% of HCCs harbouring stathmin overexpression with concomitant p53 mutation or osteopontin overexpression exhibited vascular invasion, and hence the lowest 5-year survival, p = 0.00018 and p = 0.0009, respectively. However, we did not find that stathmin overexpression exerted prognostic impact independent of tumour stage. In conclusion, stathmin expression correlates with metastatic potential, is an important prognostic factor for HCC, and may serve as a useful marker to predict ETR.

The mammalian target of rapamycin (mTOR) signaling pathway is upregulated in the pathogenesis of many cancers. Arachidonic acid (AA) and its metabolites play critical role in the development of breast cancer, but the mechanisms through which AA promotes mammary tumorigenesis and progression are poorly understood. We found that the levels of AA and cytosolic phospholipase A2 (cPLA2) strongly correlated with the signaling activity of mTORC1 and mTORC2 as well as the expression levels of vascular epithelial growth factor (VEGF) in human breast tumor tissues. In cultured breast cancer cells, AA effectively activated both mTOR complex 1 (mTORC1) and mTORC2. Interestingly, AA-stimulated mTORC1 activation was independent of amino acids, phosphatidylinositol 3-kinase (PI3-K) and tuberous sclerosis complex 2 (TSC2), which suggests a novel mechanism for mTORC1 activation. Further studies revealed that AA stimulated mTORC1 activity through destabilization of mTOR-raptor association in ras homolog enriched in brain (Rheb)-dependent mechanism. Moreover, we showed that AA-stimulated cell proliferation and angiogenesis required mTOR activity and that the effect of AA was mediated by lipoxygenase (LOX) but not cyclooxygenase-2 (COX-2). In animal models, AA-enhanced incidences of rat mammary tumorigenesis, tumor weights and angiogenesis were inhibited by rapamycin. Our findings suggest that AA is an effective intracellular stimulus of mTOR and that AA-activated mTOR plays critical roles in angiogenesis and tumorigenesis of breast cancer.

The B-cell translocation gene 3 (BTG3) is a member of the antiproliferative BTG gene family and a downstream target of p53. BTG3 also binds and inhibits E2F1. Although it connects functionally two major growth-regulatory pathways, the physiological role of BTG3 remains largely uncharacterized. Here, we present evidence that loss of BTG3 in normal cells induced cellular senescence, which was correlated with enhanced ERK-AP1 signaling and elevated expression of the histone H3K27me3 demethylase JMJD3/KDM6B, leading to acute induction of p16(INK4a). Importantly, we also found that BTG3 expression is specifically downregulated in prostate cancer, thus providing a physiological link with human cancers. Our data suggest that BTG3 may have a fail-safe role against tumorigenic progression.

Epidermal growth factor receptor (EGFR) regulates multiple signaling cascades essential for cell proliferation, growth and differentiation. Using a genetic approach, we found that Drosophila FERM and PDZ domain-containing protein tyrosine phosphatase, dPtpmeg, negatively regulates border cell migration and inhibits the EGFR/Ras/mitogen-activated protein kinase signaling pathway during wing morphogenesis. We further identified EGFR pathway substrate 15 (Eps15) as a target of dPtpmeg and its human homolog PTPN3. Eps15 is a scaffolding adaptor protein known to be involved in EGFR endocytosis and trafficking. Interestingly, PTPN3-mediated tyrosine dephosphorylation of Eps15 promotes EGFR for lipid raft-mediated endocytosis and lysosomal degradation. PTPN3 and the Eps15 tyrosine phosphorylation-deficient mutant suppress non-small-cell lung cancer cell growth and migration in vitro and reduce lung tumor xenograft growth in vivo. Moreover, depletion of PTPN3 impairs the degradation of EGFR and enhances proliferation and tumorigenicity of lung cancer cells. Taken together, these results indicate that PTPN3 may act as a tumor suppressor in lung cancer through its modulation of EGFR signaling.

The IjB kinase (IKK)/NF-jB pathway has been shown to be a major regulator in cell survival. However, the mechanisms through which IKK mediates cell death are not clear. In this study, we showed that IKK-b contributed to hydrogen peroxide (H 2 O 2 )-induced cell death independent of the NF-jB pathway. Our results demonstrated that the pro-death function of IKK-b under oxidative stress was mediated by p85 S6K1 (S6 kinase 1), but not p70 S6K1 through a rapamycin-insensitive and mammalian target of rapamycin complex 1 kinase-independent mechanism. We found that IKK-b associated with p85, but not p70 S6K1, which was required for H 2 O 2 -induced activation of p85 S6K1. IKK-b and p85 S6K1 contributed to H 2 O 2 -induced phosphorylation of Mdm2 (S166) and p53 accumulation. p85 S6K1 is critical for IKK-b-mediated cell death. Thus, these findings established a novel oxidative stress-responsive pathway that involves IKK-b, p85 S6K1 and Mdm2, which is response for H 2 O 2 -induced cell death. Our results have important implications for IKK-b and p85 S6K1 as potential targets for the prevention of diseases involved in oxidative stress-induced aberrant cell death. Reactive oxygen species (ROS), such as hydrogen peroxide (H 2 O 2 ), are generated in cells as a consequence of oxidative metabolism. Although low levels of ROS are usually detoxified quickly by antioxidant enzymes, an excessive accumulation of ROS may result in oxidative stress. High and/or persistent levels of oxidative stress represent a major cause of cellular damage and aberrant death in a plethora of pathological conditions during the initiation and progression of a plethora of pathological conditions, including neurodegenerative diseases, cancer, autoimmune and the ageing process.1 While ROS may trigger cell death through multiple mechanisms, 2 recent studies have established the nuclear factor-kB (NF-kB) pathway as a critical signaling pathway in mediating the action of ROS in cell survival/cell death.

BTG3 (B-cell translocation gene 3) is a p53 target that also binds and inhibits E2F1. Although it connects two major growth-regulatory pathways functionally and is downregulated in human cancers, whether and how BTG3 acts as a tumor suppressor remain largely uncharacterized. Here we present evidence that BTG3 binds and suppresses AKT, a kinase frequently deregulated in cancers. BTG3 ablation results in increased AKT activity that phosphorylates and inhibits glycogen synthase kinase 3β. Consequently, we also observed elevated β-catenin/T-cell factor activity, upregulation of mesenchymal markers, and enhanced cell migration. Consistent with these findings, BTG3 overexpression suppressed tumor growth in mouse xenografts, and was associated with diminished AKT phosphorylation and reduced β-catenin in tissue specimens. Significantly, a short BTG3-derived peptide was identified, which recapitulates these effects in vitro and in cells. Thus, our study provides mechanistic insights into a previously unreported AKT inhibitory pathway downstream of p53. The identification of an AKT inhibitory peptide also unveils a new avenue for cancer therapeutics development.