Kinase-inactive glycogen synthase kinase 3beta promotes Wnt signaling and mammary tumorigenesis

Recent studies have implicated ectopic activation of the Wnt pathway in many human cancers, including breast cancer. beta-catenin is a critical coactivator in this signaling pathway and is regulated in a complex fashion by phosphorylation, degradation, and nuclear translocation. Glycogen synthase kinase 3beta (GSK3beta) phosphorylation of the NH2-terminal domain of beta-catenin targets it for ubiquitination and proteosomal degradation. We hypothesized that expression of kinase-inactive GSK3beta (KI-GSK3beta) in mammary glands would function in a dominant-negative fashion by antagonizing the endogenous activity of GSK3beta and promoting breast cancer development. Consistent with this, we find that KI-GSK3beta stabilizes beta-catenin expression, catalyzes its localization to the nucleus, and up-regulates the downstream target gene, cyclin D1, in vitro. In vivo, transgenic mice overexpressing the KI-GSK3beta under the control of the mouse mammary tumor virus-long terminal repeat develop mammary tumors with overexpression of beta-catenin and cyclin D1. Thus, antagonism of GSK3beta activity is oncogenic in the mammary epithelium; mutation or pharmacologic down-regulation of GSK3beta could promote mammary tumors.     

Mutational and nonmutational activation of p21ras in rat colonic azoxymethane-induced tumors: effects on mitogen-activated protein kinase, cyclooxygenase-2, and cyclin D1

Azoxymethane (AOM)-induced colonic carcinogenesis involves a number of mutations, including those in the K-ras gene and CTNNB1, that codes for beta-catenin. Prior in vitro studies have also demonstrated that wild type p21(K-ras) can be activated by epigenetic events. We identified 15 K-ras mutations in 14 of 84 AOM-induced colonic tumors by three independent methods. By single strand conformational polymorphism, we also observed mutations in 22 of 68 tumors in exon 3 of CTNNB1. A highly sensitive method was then used to measure p21ras activation levels. All tumors assayed possessing K-ras mutations had significantly higher p21ras activation levels (8.8 +/- 1.5%; n = 13) compared with that of control colon (3.7 +/- 0.4; n = 6; P < 0.05) or tumors without such mutations (4.2 +/- 0.4%; n = 70; P < 0.05). Among tumors with wild-type K-ras, there was a subset of tumors (18 of 70) that had significantly higher p21ras activation levels (8.0 +/- 0.9%; n = 18) compared with control colons. In three of four tumors examined with activated wild-type p21ras, we observed increased c-erbB-2 receptor expression and decreased Ras-GAP expression. In contrast, only one of eight tumors examined with wild-type ras and nonactivated p21ras demonstrated these alterations. Mitogen-activated protein kinase (MAPK) activation and cyclooxygenase-2 (COX-2) expression were increased in tumors with mutated or activated wild-type p21ras, compared with their nonactivated counterparts. Although beta-catenin mutations did not alter COX-2 expression or MAPK activity, mutations in either K-ras or beta-catenin significantly increased cyclin D1 expression. In contrast, in tumors with wild-type but activated p21-ras, cyclin D1 expression was not enhanced. Thus, the spectrum of changes in MAPK, COX-2, and cyclin D1 is distinct among tumors with ras or beta-catenin mutations or nonmutational activation of p21ras.     

Activation of ERK1/2 and cyclin D1 expression in oral tongue squamous cell carcinomas: relationship between clinicopathological appearances and cell proliferation

We report an immunohistochemical investigation of the expression of activated extracellular signal-regulated kinase (ERK1/2) and cyclin D1 protein in both oral tongue squamous cell carcinomas (OTSCCs) and normal tongue epithelium. The expression of Ki-67 labeling index (LI) was also examined in order to evaluate cell proliferation activity. The expression of activated ERK1/2, cyclin D1 protein and Ki-67 LI were significantly stronger in OTSCCs than in normal oral mucosa (P<0.05). Both over-expression of activated ERK1/2 and positive expression of Ki-67 in OTSCCs were significantly associated with a moderately or poorly differentiated grade of carcinoma (P<0.05). Cyclin D1 immunostaining showed statistically significant association with both lymph node metastasis (P<0.05) and a tumor thickness >5mm (P<0.05). Over-expression of activated ERK1/2 was positively correlated with cyclin D1 protein expression (P<0.05, r=0.624) and cell proliferation-related indexes Ki-67 (P<0.05, r=0.723). Our results suggest that over-expression of activated ERK1/2 and cyclin D1 protein are involved in oral tongue carcinogenesis, and that activation of ERK1/2 might be related to cell cycle regulation and cell proliferation in OTSCCs.     

Activation of beta-catenin in epithelial and mesenchymal hepatoblastomas

Wnt/beta-catenin signaling is frequently activated in cancer cells by stabilizing mutations of beta-catenin or loss-of-function mutations of the APC tumor suppressor gene. We have analysed the role of beta-catenin in the pathogenesis of hepatoblastoma (HB), an embryonic liver tumor occurring mainly in children under 2 years of age. Sequence analysis of the beta-catenin NH2-terminal domain in 18 epithelial and mixed HBs revealed missense mutations in the GSK3beta phosphorylation motif or interstitial deletions in 12 tumors (67%). In the remaining cases, no truncating mutation of APC could be evidenced. Immunohistochemical analysis of beta-catenin in 11 HBs demonstrated nuclear/cytoplasmic accumulation of the protein in all tumors analysed, with predominant nuclear beta-catenin immunostaining in undifferentiated cells. Membranous beta-catenin localization was preserved only in fetal-type tumoral hepatocytes and was associated with E-cadherin expression. Moreover, we show that beta-catenin is aberrantly overexpressed in a large spectrum of tumor components, including hepatocyte-like cells at various differentiation stages and heterologous elements such as squamous, osteoid and chrondroid tissues, and in occasional other mesenchymally-derived cells. These data strongly suggest that activation of beta-catenin signaling is an obligatory step in HB pathogenesis, and raise the possibility that it interferes with developmental signals that specify different tissue types at early stages of hepatic differentiation.     

Differential signaling pathways are activated in the Epstein-Barr virus-associated malignancies nasopharyngeal carcinoma and Hodgkin lymphoma

EBV is associated with the epithelial cancer, nasopharyngeal carcinoma (NPC), and the lymphoid malignancy, Hodgkin lymphoma (HL). The EBV latent membrane proteins 1 and 2A are expressed in these tumors. These proteins activate the phosphatidylinositol 3'-OH kinase (PI3K)/Akt pathway, which is commonly activated inappropriately in malignancy. In this study, the status of Akt activation and its targets, glycogen synthase kinase-3beta (GSK-3beta) and beta-catenin, was investigated in NPC and HL clinical specimens. In the majority of HL and NPC specimens, Akt was activated, indicating an important role for this kinase in the development and/or progression of these tumors. Akt phosphorylates and inactivates GSK-3beta, a negative regulator of the proto-oncoprotein beta-catenin that is aberrantly activated in many cancers. GSK-3beta was phosphorylated and inactivated with concomitant nuclear beta-catenin accumulation in the majority of NPC specimens. The malignant cells of the majority of HL cases, however, did not have inactivated GSK-3beta and lacked nuclear beta-catenin expression. These data indicate that this signaling arm of PI3K/Akt is universal and important in NPC pathogenesis but is apparently not affected in HL. These findings point to a divergence in pathways activated by EBV in different cellular contexts.     

beta-Catenin mutation in rat colon tumors initiated by 1,2-dimethylhydrazine and 2-amino-3-methylimidazo[4,5-f]quinoline, and the effect of post-initiation treatment with chlorophyllin and indole-3-carbinol

Carcinogens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 1,2-dimethylhydrazine (DMH) induce colon tumors in the rat that contain mutations in beta-catenin, but the pattern of mutation differs from that found in human colon cancers. In both species, mutations affect the glycogen synthase kinase-3beta consensus region of beta-catenin, but whereas they directly substitute critical Ser/Thr phosphorylation sites in human colon cancers, the majority of mutations cluster around Ser33 in the rat tumors. Two dietary phytochemicals, chlorophyllin and indole-3-carbinol, given post-initiation, shifted the pattern of beta-catenin mutations in rat colon tumors induced by IQ and DMH. Specifically, 17/39 (44%) of the beta-catenin mutations in groups given carcinogen plus modulator were in codons 37, 41 and 45, and substituted critical Ser/Thr residues directly, as seen in human colon cancers. None of the tumors from groups given carcinogen alone had mutations in these codons. Interestingly, many of the mutations that substituted critical Ser/Thr residues in beta-catenin were from a single group given DMH and 0.001% chlorophyllin, in which a statistically significant increase in colon tumor multiplicity was observed compared with the group given DMH only. These tumors had marked over-expression of cyclin D1, c-myc and c-jun mRNA and c-Myc and c-Jun proteins were strongly elevated compared with tumors containing wild-type beta-catenin. The results indicate that the pattern of beta-catenin mutations in rat colon tumors can be influenced by exposure to dietary phytochemicals administered post-initiation, and that the mechanism might involve the altered expression of beta-catenin/Tcf/Lef target genes.     

Involvement of PI3K/AKT/GSK3beta pathway in tetrandrine-induced G1 arrest and apoptosis

It has been reported that tetrandrine induces cell cycle arrest and apoptosis in human cancer cells. In the present study, we investigated the role of PI3K/AKT/GSK3beta pathway in tetrandrine- induced G(1) arrest and apoptosis. In HT-29 cells, tetrandrine induced dephosphorylation of AKT, activation and nuclear translocation of GSK3beta as well as upregulation of p27(kip1). Activation of GSK3beta via AKT inhibitoion induced by tetrandrine resulted in enhanced phosphorylation and proteolysis of cyclin D(1), activation of caspase 3 and subsequent cleavage of PARP. Selective GSK3beta inhibitiors and GSK3beta siRNA attenuated tetrandrine-induced G(1) arrest and apoptosis. Similar to tetrandrine, transfection of wild-type GSK3beta led to G(1) arrest and apoptosis via downregulation of cyclin D(1) and cleavage of PARP. These findings suggest that tetrandrine induces G(1) arrest and apoptosis through PI3K/AKT/GSK3beta pathway and identify GSK3beta as an important mediator in the processes.     

Aberrant expression of beta-catenin, Pin1 and cylin D1 in salivary adenoid cystic carcinoma: relation to tumor proliferation and metastasis

The aims of this study were to investigate the expression levels of beta-catenin, Pin1 and cyclin D1 in salivary adenoid cystic carcinomas (SACC ) and to evaluate its clinical importance, furthermore, to elucidate whether beta-catenin expression was aberrant in SACC and whether Pin1 was involved in aberrant beta-catenin and cyclin D1 expression. The expression of Pin1, beta-catenin and cyclin D1 were examined in the specimens of 65 patients with SACC by immunohistochemistry, protein and mRNA expressions were detected by western blotting and RT-PCR in four SACC cell lines. Pin1 was overexpressed in 51 cases of SACC (78%), and high levels of Pin1 expression correlated with cyclin D1 positive expression (p = 0.02). Fourteen (22%) cases showed positive immunoreactivity for beta-catenin protein in the nuclear/cytoplasmic fraction in tumor tissues, which was defined as cytoplasm/nucleus staining, among which quite evident nuclear expression of beta-catenin was detected in six cases (9%), while cyclin D1 positive expression was detected in 41 cases of SACC (63%). Reduced membranous expression of beta-catenin was detected in the cases with metastasis (11/14). Theses results suggest that Pin1 and Wnt signalling pathway are activated in SACC and may play a pivotal role in SACC carcinogenesis and metastasis.     

A plant oxylipin, 12-oxo-phytodienoic acid,inhibits proliferation of human breast cancer cells by targeting cyclin D1

Cyclin D1 overexpression has been associated with poor prognosis and resistance to therapy in human breast cancer. Thus, the development of therapeutic agents that selectively target cyclin D1 activity is of clinical interest. This study demonstrates that 12-oxo-phytodienoic acid (OPDA), a phytohormone with critical functions in growth and development in plants, induces growth arrest in MDA-MB-231 and T47D breast cancer cells. In response to OPDA treatment, the human breast cancer cell lines exhibit a progressive decline in cyclin D1 expression, which is tightly associated with the accumulation of hypophosphorylated form of the retinoblastoma protein (Rb) and G1 arrest. The decrease in cyclin D1 protein expression accompanies a dramatic decline in nuclear but not membranous beta-catenin expression and activation of glycogen synthase kinase-3-beta (GSK3beta) caused by inhibition of its serine-9 phosphorylation. The proteasome inhibitor MG132 blocks OPDA-mediated decrease in cyclin D1. In addition, the overexpression of T286A, a cyclin D1 mutant which is refractory to phosphorylation by GSK3beta and proteosomal degradation, is resistant to OPDA-mediated Rb dephosphorylation as well as G(1) cell cycle arrest. Thus, our results demonstrate that degradation of cyclin D1 protein is a key event in OPDA induced growth inhibition in breast cancer cells. These data provide the basic foundation for future efforts to develop OPDA-based approaches in the prevention and treatment of breast cancer and other types of cancer.     

Beta-catenin and cyclin D1 expression in human hepatocellular carcinoma

To understand the nature and roles of mutated beta-catenin in human hepatocellular carcinomas (HCCs), 57 cases of surgically resected HCCs were studied. DNAs extracted from each tumor were examined for somatic mutations of exon 3, and the protein expressions of beta-catenin, cyclin D1, and Ki-67 were observed by immunohistochemical staining. beta-catenin mutations in exon 3 were detected in 10 (17.5%) out of 57 HCCs, including nine missense mutations and one deletion mutation. All of the cases with gene alterations had the anti-HCV antibody, and tested negative for the HBs antigen in the sera. All of the mutations occurred at the serine/threonine phosphorylation sites of glycogen synthase kinase-3beta (GSK-3beta) or their neighboring residues. Significant correlation with intracellular expression (p=0.00055) was shown in the HCCs harboring beta-catenin mutations. The intracellular accumulation of beta-catenin showed significant correlation with the cyclin D1 expression (p=0.00858), and with a higher proliferation index (p=0.00072). In addition, the beta-catenin mutations showed significant association with the cyclin D1 expression (p=0.0424). These results suggest that accumulated beta-catenin proteins may bind to the lymphocyte enhancer binding factor-1 (LEF-1), form the beta-catenin/LEF-1 complex, and stimulate such promoters regulating the cell cycle as the cyclin D1 gene. This is the first report to demonstrate a significant correlation between beta-catenin and the cyclin D1 expression in human HCCs.     

Mutation of beta-catenin is an early event in chemically induced mouse hepatocellular carcinogenesis.

beta-catenin activation, and subsequent upregulation of Wnt-signaling, is an important event in the development of certain human and rodent cancers. Recently, mutations in the beta-catenin gene in the region of the serine-threonine glycogen kinase (GSK)-3beta phosphorylation target sites have been identified in hepatocellular neoplasms from humans and transgenic mice. In this study we examined 152 hepatocellular neoplasms from B6C3F1 mice included in five chemical treatment groups and controls for mutations in the beta-catenin gene. Twenty of 29 hepatocellular neoplasms from mice treated with methyleugenol had point mutations at codons 32, 33, 34 or 41, sites which are mutated in colon and other cancers. Likewise, nine of 24 methylene chloride-induced hepatocellular neoplasms and 18 of 42 oxazepam-induced neoplasms exhibited similar mutations. In contrast, only three of 18 vinyl carbamate-induced liver tumors, one of 18 TCDD-induced liver tumors, and two of 22 spontaneous liver neoplasms had mutations in beta-catenin. Thus, there appears to be a chemical specific involvement of beta-catenin activation in mouse hepatocellular carcinogenesis. Expression analyses using Western blot and immunohistochemistry indicate that beta-catenin protein accumulates along cell membranes following mutation. The finding of mutations in both adenomas and carcinomas from diverse chemical treatment groups and the immunostaining of beta-catenin protein in an altered hepatocellular focus suggest that these alterations are early events in mouse hepatocellular carcinogenesis.