Yoku Hayakawa

Gremlin 1 Identifies a Skeletal Stem Cell with Bone, Cartilage, and Reticular Stromal Potential

The stem cells that maintain and repair the postnatal skeleton remain undefined. One model suggests that perisinusoidal mesenchymal stem cells (MSCs) give rise to osteoblasts, chondrocytes, marrow stromal cells, and adipocytes, although the existence of these cells has not been proven through fate-mapping experiments. We demonstrate here that expression of the bone morphogenetic protein (BMP) antagonist gremlin 1 defines a population of osteochondroreticular (OCR) stem cells in the bone marrow. OCR stem cells self-renew and generate osteoblasts, chondrocytes, and reticular marrow stromal cells, but not adipocytes. OCR stem cells are concentrated within the metaphysis of long bones not in the perisinusoidal space and are needed for bone development, bone remodeling, and fracture repair. Grem1 expression also identifies intestinal reticular stem cells (iRSCs) that are cells of origin for the periepithelial intestinal mesenchymal sheath. Grem1 expression identifies distinct connective tissue stem cells in both the bone (OCR stem cells) and the intestine (iRSCs).

Constitutive NF-κB Activation in Colorectal Carcinoma Plays a Key Role in Angiogenesis, Promoting Tumor Growth

Purpose: Nuclear factor κB (NF-κB) is an important transcription factor in various biological processes. Constitutive NF-κB activation has been noted in many tumors, including colorectal cancers. However, the precise role of this activation in colorectal cancer is unclear. Experimental Design: Constitutive NF-κB activation was evaluated in colorectal cancer tissues and cell lines. To inhibit NF-κB activation, we established cancer cells with stable knockdown of IκB kinase γ (NF-κB essential modulator), which is the regulatory subunit of the IκB kinase complex, by RNA interference. Cell growth and apoptosis were evaluated in wild-type cells (WT) and knocked-down cells (KD). Microarray and protein array analysis were also done. To determine involvement of angiogenesis, human umbilical vein endothelial cells were used. By s.c. transplantation of the cells into nude mice, tumor sizes, vascularity, and chemodrug sensitivity were analyzed. Results: Constitutive NF-κB activation was observed in 40% of colorectal cancer tissues and 67% of cell lines. Cell proliferation was not different between WT and KD in vitro, whereas apoptosis mediated by tumor necrosis factor-α and 5-fluorouracil were increased in KD. Several angiogenic chemokines were decreased in KD. Human umbilical vein endothelial cells incubated in WT supernatant showed more branch points than in KD, suggesting that constitutive NF-κB activation was involved in angiogenesis. Subcutaneous tumor expansion was suppressed to 23% in KD, and vessels were also decreased. By 5-fluoruracil treatment, tumor expansion was suppressed to a greater extent in KD (to 6%) than in WT (to 50%). Conclusion: NF-κB inhibition may represent a potent treatment modality in colorectal cancer, especially in cases with constitutive NF-κB activation.

Long-lived intestinal tuft cells serve as colon cancer–initiating cells

Doublecortin-like kinase 1 protein (DCLK1) is a gastrointestinal tuft cell marker that has been proposed to identify quiescent and tumor growth-sustaining stem cells. DCLK1⁺ tuft cells are increased in inflammation-induced carcinogenesis; however, the role of these cells within the gastrointestinal epithelium and their potential as cancer-initiating cells are poorly understood. Here, using a BAC-CreERT-dependent genetic lineage-tracing strategy, we determined that a subpopulation of DCLK1⁺ cells is extremely long lived and possesses rare stem cell abilities. Moreover, genetic ablation of Dclk1 revealed that DCLK1⁺ tuft cells contribute to recovery following intestinal and colonic injury. Surprisingly, conditional knockdown of the Wnt regulator APC in DCLK1⁺ cells was not sufficient to drive colonic carcinogenesis under normal conditions; however, dextran sodium sulfate-induced (DSS-induced) colitis promoted the development of poorly differentiated colonic adenocarcinoma in mice lacking APC in DCLK1⁺ cells. Importantly, colonic tumor formation occurred even when colitis onset was delayed for up to 3 months after induced APC loss in DCLK1⁺ cells. Thus, our data define an intestinal DCLK1⁺ tuft cell population that is long lived, quiescent, and important for intestinal homeostasis and regeneration. Long-lived DCLK1⁺ cells maintain quiescence even following oncogenic mutation, but are activated by tissue injury and can serve to initiate colon cancer.

Denervation suppresses gastric tumorigenesis.

Surgical or pharmacologic interruption of muscarinic innervation to the stomach suppresses gastric tumor growth in mice and humans. Treating Cancer by Getting on Its Nerves The nervous system plays a role in the regulation of many different organs, including the gut. Now, Zhao et al. have shown that the vagal nerve, which signals to the stomach through muscarinic receptors, contributes to the growth of gastric tumors. The authors demonstrated that vagotomy (surgical interruption of the vagal nerve) can prevent gastric cancer in mice and reduce the recurrence of gastric tumors in human patients. Moreover, the same result can be achieved in mice treated with Botox or anticholinergic drugs to inhibit vagal nerve signaling, raising the hope of a safer treatment for gastric cancer without irreversible side effects. The nervous system plays an important role in the regulation of epithelial homeostasis and has also been postulated to play a role in tumorigenesis. We provide evidence that proper innervation is critical at all stages of gastric tumorigenesis. In three separate mouse models of gastric cancer, surgical or pharmacological denervation of the stomach (bilateral or unilateral truncal vagotomy, or local injection of botulinum toxin type A) markedly reduced tumor incidence and progression, but only in the denervated portion of the stomach. Vagotomy or botulinum toxin type A treatment also enhanced the therapeutic effects of systemic chemotherapy and prolonged survival. Denervation-induced suppression of tumorigenesis was associated with inhibition of Wnt signaling and suppression of stem cell expansion. In gastric organoid cultures, neurons stimulated growth in a Wnt-mediated fashion through cholinergic signaling. Furthermore, pharmacological inhibition or genetic knockout of the muscarinic acetylcholine M3 receptor suppressed gastric tumorigenesis. In gastric cancer patients, tumor stage correlated with neural density and activated Wnt signaling, whereas vagotomy reduced the risk of gastric cancer. Together, our findings suggest that vagal innervation contributes to gastric tumorigenesis via M3 receptor–mediated Wnt signaling in the stem cells, and that denervation might represent a feasible strategy for the control of gastric cancer.

Serum IL-6 levels and the risk for hepatocarcinogenesis in chronic hepatitis C patients: an analysis based on gender differences

Interleukin‐6 (IL‐6) may play a role in the pathogenesis of hepatocellular carcinoma (HCC). Recently, it was reported in mouse models that estrogen‐mediated inhibition of IL‐6 production explains the gender disparity in HCC. We conducted a retrospective cohort study to examine whether this hypothesis is applicable to human HCC. We enrolled 330 patients with chronic hepatitis C whose serum samples were collected between January 1994 and December 2002. Serum IL‐6 concentrations were measured and patients were divided into three groups according to IL‐6 levels: low, middle, and high. We evaluated the association between serum IL‐6 levels and the risk of subsequent HCC development, including subgroup analysis on each gender. During the follow‐up period (mean 9.0 yr), HCC developed in 126 patients. The incidence rates differed significantly among the three groups (p = 0.015), increasing in accordance with serum IL‐6 levels. However, unexpectedly, this tendency was significant only in female patients. In a multivariate analysis, higher serum IL‐6 level was an independent risk factor for HCC development in female patients, with a hazard ratio of 1.61. Although female patients showed a weak negative correlation between serum IL‐6 levels and estradiol levels, the lower risk of HCC in female patients cannot be fully explained by estrogen‐mediated inhibition of IL‐6 production. In conclusion, higher serum IL‐6 level was an independent risk factor for HCC development in female but not male chronic hepatitis C patients. Measurement of serum IL‐6 levels may provide useful information for predicting future HCC development in female chronic hepatitis C patients.

Krt19+/Lgr5− Cells Are Radioresistant Cancer-Initiating Stem Cells in the Colon and Intestine

Epithelium of the colon and intestine are renewed every 3 days. In the intestine there are at least two principal stem cell pools. The first contains rapid cycling crypt-based columnar (CBC) Lgr5(+) cells, and the second is composed of slower cycling Bmi1-expressing cells at the +4 position above the crypt base. In the colon, however, the identification of Lgr5(-) stem cell pools has proven more challenging. Here, we demonstrate that the intermediate filament keratin-19 (Krt19) marks long-lived, radiation-resistant cells above the crypt base that generate Lgr5(+) CBCs in the colon and intestine. In colorectal cancer models, Krt19(+) cancer-initiating cells are also radioresistant, while Lgr5(+) stem cells are radiosensitive. Moreover, Lgr5(+) stem cells are dispensable in both the normal and neoplastic colonic epithelium, as ablation of Lgr5(+) stem cells results in their regeneration from Krt19-expressing cells. Thus, Krt19(+) stem cells are a discrete target relevant for cancer therapy.

Apoptosis signal-regulating kinase 1 and cyclin D1 compose a positive feedback loop contributing to tumor growth in gastric cancer.

Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular functions and are highly active in many types of human cancers. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream MAPK involved in apoptosis, inflammation, and carcinogenesis. This study investigated the role of ASK1 in the development of gastric cancer. In human gastric cancer specimens, we observed increased ASK1 expression, compared to nontumor epithelium. Using a chemically induced murine gastric tumorigenesis model, we observed increased tumor ASK1 expression, and ASK1 knockout mice had both fewer and smaller tumors than wild-type (WT) mice. ASK1 siRNA inhibited cell proliferation through the accumulation of cells in G1 phase of the cell cycle, and reduced cyclin D1 expression in gastric cancer cells, whereas these effects were uncommon in other cancer cells. ASK1 overexpression induced the transcription of cyclin D1, through AP-1 activation, and ASK1 levels were regulated by cyclin D1, via the Rb–E2F pathway. Exogenous ASK1 induced cyclin D1 expression, followed by elevated expression of endogenous ASK1. These results indicate an autoregulatory mechanism of ASK1 in the development of gastric cancer. Targeting this positive feedback loop, ASK1 may present a potential therapeutic target for the treatment of advanced gastric cancer.

Ikappa B kinaseβ/nuclear factor‐κB activation controls the development of liver metastasis by way of interleukin‐6 expression

Nuclear factor kappaB (NF‐κB) plays an important role in the regulation of innate immune responses, apoptosis, inflammation, and oncogenesis. NF‐κB activation in the liver was observed after intrasplenic administration of a lung carcinoma cell line, LLC, which induces liver metastasis. To explore the role of Ikappa B kinase beta (IKKβ), which is the critical kinase of the IKK complex, and NF‐κB activation in metastasis, we injected LLC cells into hepatocyte‐specific IKKβ knockout mice (IkkβΔhep), whole‐liver knockout (IkkβΔL+H) mice, and control (IkkβF/F) mice. IkkβΔL+H mice developed liver metastasis with significantly lower liver weights and fewer metastatic foci compared to IkkβΔhep and IkkβF/F mice. Furthermore, intrasplenic LLC injection induced the messenger RNA (mRNA) expression of interleukin (IL)‐6 and IL‐1β in IkkβF/F mice, whereas these genes were less expressed in IkkβΔL+H mice. IL‐6−/− mice and treatment with anti‐IL‐6 receptor antibody showed a lesser degree of metastatic tumor, indicating that IL‐6 is associated with liver metastasis. Conclusion: Collectively, these observations suggest that IKKβ/NF‐κB activation controls the development of liver metastasis by way of IL‐6 expression and is a potential target for the development of antimetastatic drugs. (HEPATOLOGY 2009.)

Loss of liver E-cadherin induces sclerosing cholangitis and promotes carcinogenesis

Significance The precise roles of E-cadherin in the liver and liver carcinogenesis are still unknown. Here we show that mice lacking E-cadherin in the liver develop spontaneous periportal inflammation via an impaired intrahepatic biliary network, as well as periductal fibrosis, which resembles primary sclerosing cholangitis. Inducible gene knockout studies identified E-cadherin loss in biliary epithelial cells as a causal factor of cholangitis induction, and dysregulated E-cadherin expression was also seen in patients with primary sclerosing cholangitis. E-cadherin loss also significantly accelerates genetically and chemically engineered liver cancer through epithelial–mesenchymal transition, up-regulation of stem cell markers, and ERK activation. Thus, E-cadherin plays critical roles in maintaining homeostasis and suppressing carcinogenesis in the liver. E-cadherin is an important adhesion molecule whose loss is associated with progression and poor prognosis of liver cancer. However, it is unclear whether the loss of E-cadherin is a real culprit or a bystander in liver cancer progression. In addition, the precise role of E-cadherin in maintaining liver homeostasis is also still unknown, especially in vivo. Here we demonstrate that liver-specific E-cadherin knockout mice develop spontaneous periportal inflammation via an impaired intrahepatic biliary network, as well as periductal fibrosis, which resembles primary sclerosing cholangitis. Inducible gene knockout studies identified E-cadherin loss in biliary epithelial cells as a causal factor of cholangitis induction. Furthermore, a few of the E-cadherin knockout mice developed spontaneous liver cancer. When knockout of E-cadherin is combined with Ras activation or chemical carcinogen administration, E-cadherin knockout mice display markedly accelerated carcinogenesis and an invasive phenotype associated with epithelial–mesenchymal transition, up-regulation of stem cell markers, and elevated ERK activation. Also in human hepatocellular carcinoma, E-cadherin loss correlates with increased expression of mesenchymal and stem cell markers, and silencing of E-cadherin in hepatocellular carcinoma cell lines causes epithelial–mesenchymal transition and increased invasiveness, suggesting that E-cadherin loss can be a causal factor of these phenotypes. Thus, E-cadherin plays critical roles in maintaining homeostasis and suppressing carcinogenesis in the liver.

Apoptosis Signal-Regulating Kinase 1 Inhibits Hepatocarcinogenesis by Controlling the Tumor-Suppressing Function of Stress-Activated Mitogen-Activated Protein Kinase

The stress‐activated mitogen‐activated protein kinases (MAPKs), c‐Jun NH2‐terminal kinase (JNK), and p38 have been implicated in hepatocarcinogenesis. Although the many interrelated functions of JNK and p38 are precisely regulated by upstream signaling molecules, little is known about upstream regulators. We investigated the role of apoptosis signal‐regulating kinase 1 (ASK1), a major player in the regulation of JNK and p38 activities, in hepatocarcinogenesis using a mouse hepatocellular carcinoma (HCC) model. ASK1‐deficient (ASK1−/−) and wildtype (WT) mice were treated with diethylnitrosamine on postnatal day 14. Strikingly, after 7 months, approximately three times as many tumors developed in ASK1−/− mice as in WT mice. Although JNK and p38 activation were attenuated in ASK1−/− HCCs relative to WT HCCs, cell proliferation was comparable in HCCs from both types of mice. On the other hand, both cancer cell apoptosis and hyperphosphorylation of BimEL, a proapoptotic Bcl‐2 family member, were suppressed in the ASK1−/− HCCs. ASK1−/− mice showed remarkable resistance to Fas‐induced hepatocyte apoptosis in vivo, probably because of attenuated JNK‐mediated BimEL phosphorylation and mitochondrial apoptotic pathway activation. The reintroduction of ASK1 to ASK1−/− mouse liver using an adenoviral vector restored Fas‐induced hepatocyte death and phosphorylation of JNK and BimEL. Similar findings were obtained in tumor necrosis factor alpha‐induced hepatocyte apoptosis. Furthermore, ASK1 was involved in DNA damage‐induced p21 up‐regulation through a p38 pathway. Conclusion: ASK1 is involved in death receptor‐mediated apoptosis and DNA‐damage response by way of stress‐activated MAPK in the liver, and thus acts as a tumor suppressor in hepatocarcinogenesis. This study provides new insight into the regulation of stress‐ activated MAPK signaling in hepatocarcinogenesis. (HEPATOLOGY 2011;)