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.