HBO1 promotes cell proliferation in bladder cancer via activation of Wnt/β‐catenin signaling

Histone acetyltransferase binding to ORC1 (HBO1), a histone acetyltransferase, was recently identified as an oncoprotein; however, its role in bladder cancer remains unknown. In this study, we showed that HBO1 was highly expressed at both the mRNA and the protein levels in bladder cancer. HBO1 expression was associated with the clinical features of human bladder cancer, including tumor size (P = 0.018) and T (P = 0.007) classifications. Patients with higher HBO1 expression had shorter recurrence‐free survival time, whereas patients with lower HBO1 expression had better survival time. Moreover, we found that ectopic overexpression of HBO1 promoted, whereas HBO1 silencing inhibited tumor growth in bladder cancer cells both in vitro and in vivo. We further demonstrated that upregulation of HBO1 activated the Wnt/β‐catenin signaling pathway and led to nuclear localization of β‐catenin and upregulation of downstream targets of of Wnt/β‐catenin signaling. These findings suggest that HBO1 plays a key role in the progression of bladder cancer via the Wnt/β‐catenin pathway, and may serve as a potential therapeutic target for the treatment of bladder cancer.     

Liver specific overexpression of platelet‐derived growth factor‐B accelerates liver cancer development in chemically induced liver carcinogenesis

A genetic basis of hepatocellular carcinoma (HCC) has been well‐established and major signaling pathways, such as p53, Wnt‐signaling, transforming growth factor‐β (TGF‐β) and Ras pathways, have been identified to be essential to HCC development. Lately, the family of platelet‐derived growth factors (PDGFs) has shifted to the center of interest. We have reported on spontaneously developing liver fibrosis in PDGF‐B transgenic mice. Since HCC rarely occurs in healthy liver, but dramatically increases at the cirrhosis stage of which liver fibrosis is a preliminary stage, we investigated liver cancer development in chemically induced liver carcinogenesis in these mice. HCC induction was performed by treatment of the mice with diethylnitrosamine and phenobarbital. At an age of 6 months, the tumor development of these animals was analyzed. Not only the development of dysplastic lesions in PDGF‐B transgenic mice was significantly increased but also their malignant transformation to HCC. Furthermore, we were able to establish a key role of PDGF‐B signaling at diverse stages of liver cancer development. Here, we show that development of liver fibrosis is likely through upregulation of TGF‐β receptors by PDGF‐B. Additionally, overexpression of PDGF‐B also leads to an increased expression of β‐catenin as well as vascular endothelial growth factor and platelet endothelial cell adhesion molecule‐1 (PECAM‐1/CD31), all factors with established roles in carcinogenesis. We were able to extend the understanding of key genetic regulators in HCC development by PDGF‐B and decode essential downstream signals.     

Context‐dependent activation of Wnt signaling by tumor suppressor RUNX3 in gastric cancer cells

RUNX3 is a tumor suppressor for a variety of cancers. RUNX3 suppresses the canonical Wnt signaling pathway by binding to the TCF4/β‐catenin complex, resulting in the inhibition of binding of the complex to the Wnt target gene promoter. Here, we confirmed that RUNX3 suppressed Wnt signaling activity in several gastric cancer cell lines; however, we found that RUNX3 increased the Wnt signaling activity in KatoIII and SNU668 gastric cancer cells. Notably, RUNX3 expression increased the ratio of the Wnt signaling‐high population in the KatoIII cells. although the maximum Wnt activation level of individual cells was similar to that in the control. As found previously, RUNX3 also binds to TCF4 and β‐catenin in KatoIII cells, suggesting that these molecules form a ternary complex. Moreover, the ChIP analyses revealed that TCF4, β‐catenin and RUNX3 bind the promoter region of the Wnt target genes, Axin2 and c‐Myc, and the occupancy of TCF4 and β‐catenin in these promoter regions is increased by the RUNX3 expression. These results suggest that RUNX3 stabilizes the TCF4/β‐catenin complex on the Wnt target gene promoter in KatoIII cells, leading to activation of Wnt signaling. Although RUNX3 increased the Wnt signaling activity, its expression resulted in suppression of tumorigenesis of KatoIII cells, indicating that RUNX3 plays a tumor‐suppressing role in KatoIII cells through a Wnt‐independent mechanism. These results indicate that RUNX3 can either suppress or activate the Wnt signaling pathway through its binding to the TCF4/β‐catenin complex by cell context‐dependent mechanisms.     

ATP‐P2Y2‐β‐catenin axis promotes cell invasion in breast cancer cells

Extracellular adenosine 5′‐triphosphate (ATP), secreted by living cancer cells or released by necrotic tumor cells, plays an important role in tumor invasion and metastasis. Our previous study demonstrated that ATP treatment in vitro could promote invasion in human prostate cancer cells via P2Y2, a preferred receptor for ATP, by enhancing EMT process. However, the pro‐invasion mechanisms of ATP and P2Y2 are still poorly studied in breast cancer. In this study, we found that P2Y2 was highly expressed in breast cancer cells and associated with human breast cancer metastasis. ATP could promote the in vitro invasion of breast cancer cells and enhance the expression of β‐catenin as well as its downstream target genes CD44, c‐Myc and cyclin D1, while P2Y2 knockdown attenuated above ATP‐driven events in vitro and in vivo. Furthermore, iCRT14, a β‐catenin/TCF complex inhibitor, could also suppress ATP‐driven migration and invasion in vitro. These results suggest that ATP promoted breast cancer cell invasion via P2Y2‐β‐catenin axis. Thus blockade of the ATP‐P2Y2‐β‐catenin axis could suppress the invasive and metastatic potential of breast cancer cells and may serve as potential targets for therapeutic interventions of breast cancer.     

Dkk3, downregulated in cervical cancer,functions as a negative regulator of β‐catenin

The Wnt/β‐catenin signaling pathway is activated during the malignant transformation of keratinocytes that originate from the human uterine cervix. Dkk1, 2 and 4 have been shown to modulate the Wnt‐induced stabilization of the β‐catenin signaling pathway. However, the function of Dkk3 in this pathway is unknown. Comparison of the Dkk3 gene expression profiles in cervical cancer and normal cervical tissue by cDNA microarray and subsequent real‐time PCR revealed that the Dkk3 gene is frequently downregulated in the cancer. Methylation studies showed that the promoter of Dkk3 was methylated in cervical cancer cell lines and 22 (31.4%) of 70 cervical cancer tissue specimens. This promoter methylation was associated with reduced expression of Dkk3 mRNA in the paired normal and tumor tissue samples. Further, the reintroduction of Dkk3 into HeLa cervical cancer cells resulted in reduced colony formation and retarded cell growth. The forced expression of Dkk3 markedly attenuated β‐catenin‐responsive luciferase activity in a dose‐dependent manner and decreased the β‐catenin levels. By utilizing a yeast two‐hybrid screen, βTrCP, a negative regulator of β‐catenin was identified as a novel Dkk3‐interacting partner. Coexpression with βTrCP synergistically enhanced the inhibitory function of Dkk3 on β‐catenin. The stable expression of Dkk3 blocks the nuclear translocation of β‐catenin, resulting in downregulation of its downstream targets (VEGF and cylcin D), whereas knockdown of Dkk3 abrogates this blocking. We conclude from our finding that Dkk3 is a negative regulator of β‐catenin and its downregulation contribute to an activation of the β‐catenin signaling pathway. © 2008 Wiley‐Liss, Inc.     

HBx mutations promote hepatoma cell migration through the Wnt/β‐catenin signaling pathway

HBx mutations (T1753V, A1762T, G1764A, and T1768A) are frequently observed in hepatitis B virus (HBV)‐related hepatocellular carcinoma (HCC). Aberrant activation of the Wnt/β‐catenin signaling pathway is involved in the development of HCC. However, activation of the Wnt/β‐catenin signaling pathway by HBx mutants has not been studied in hepatoma cells or HBV‐associated HCC samples. In this study, we examined the effects of HBx mutants on the migration and proliferation of HCC cells and evaluated the activation of Wnt/β‐catenin signaling in HBx‐transfected HCC cells and HBV‐related HCC tissues. We found that HBx mutants (T, A, TA, and Combo) promoted the migration and proliferation of hepatoma cells. The HBx Combo mutant potentiated TOP‐luc activity and increased nuclear translocation of β‐catenin. Moreover, the HBx Combo mutant increased and stabilized β‐catenin levels through inactivation of glycogen synthase kinase‐3β, resulting in upregulation of downstream target genes such as c‐Myc, CTGF, and WISP2. Enhanced activation of Wnt/β‐catenin was found in HCC tissues with HBx TA and Combo mutations. Knockdown of β‐catenin effectively abrogated cell migration and proliferation stimulated by the HBx TA and Combo mutants. Our results indicate that HBx mutants, especially the Combo mutant, allow constitutive activation of the Wnt signaling pathway and may play a pivotal role in HBV‐associated hepatocarcinogenesis.