β-catenin signaling and regulation of cyclin D1 promoter in NRK-49F cells transformed by down-regulation of the tumor suppressor lysyl oxidase

Abstract

Lysyl oxidase is the enzyme that is essential for collagen and elastin cross-linking. Previous investigations showed that lysyl oxidase is down-regulated in many human tumors and ras-transformed cells. Recently, we proved that antisense down-regulation of lysyl oxidase in NRK-49F cells induced phenotypic changes and oncogenic transformation, characterized by p21(ras) activation and beta-catenin/cyclin D1 up-regulation. In the present paper, we examined beta-catenin intracellular distribution and its association with E-cadherin. We observed an increased association between E-cadherin and beta-catenin in the lysyl-oxidase down-regulated cells during serum starvation. Moreover, we found that beta-catenin cytoplasmic and nuclear levels were increased, suggesting a failure of its down-regulation by the APC-GSK-3beta system, in particular the GSK-3beta phosphorylation of ser-33/37 and thr-41 of beta-catenin. Finally, we investigated the mechanisms leading to the observed cyclin D1 up-regulation. We showed that in the antisense lysyl oxidase cells the cyclin D1 promoter was activated through the LEF and the ATF/CRE sites in the proximal promoter. While the promoter activation through LEF is compatible with beta-catenin signaling, we investigated the possibility that the CRE-dependent activation might be linked to the down-regulation of lysyl oxidase. In fact, up-regulation of lysyl oxidase in a COS-7 cell model showed a significant diminution of the CREB protein binding to the cyclin D1 promoter, leading to a dramatic inhibition of its activity and a significant down-regulation of cyclin D1 protein level in vivo. Finally, our study describes some major anomalies occurring in lysyl oxidase down-regulated fibroblasts, related to beta-catenin signaling and cyclin D1 expression.

Lysyl oxidase: an oxidative enzyme and effector of cell function

“…These results point to a unique mechanism of regulation of carcinoma progression involving LOXL proteins [69,70]. Giampuzzi et al [71] reported the oncogenic transformation of normal rat kidney fibroblasts (NRK-49F) by transfecting with antisense LOX cDNA [71]. β-Catenin was upregulated as was cyclinD1 while the ras oncogene became activated in response to the downregulation of LOX in these cells.…”

Role of lysyl oxidase in myocardial fibrosis: from basic science to clinical aspects

“…Recent reports have demonstrated novel roles for LOX, including its involvement in motility and migration in fibroblasts (50) and regulation of cell adhesion (20). In addition, LOX expression and activity have been observed in the cytoplasm and nucleus (29) and implicated in cell signaling and transcriptional gene regulation, as evidenced by the activation of the collagen III ␣ 1 -promoter through LOX-induced binding of Ku antigen (18).…”

Lysyl Oxidase Mediates Hypoxic Control of Metastasis

“…Previous reports have shown that genetic inhibition of LOX increases cell proliferation, again supporting the idea that LOX acts as a tumor suppressor. Mechanistically, LOX is thought to affect fibroblast proliferation through elevated cyclin D1, as antisense down-regulation of LOX in rat kidney fibroblasts increases cyclin D1 expression through hcatenin signaling (11). Recently, it was reported that it is the COOH-terminal propeptide region of LOX that acts intracellularly to suppress transformation of fibroblast by Ras (12).…”