Down-regulation of lysyl oxidase-induced tumorigenic transformation in NRK-49F cells characterized by constitutive activation of Ras proto-oncogene

Several investigations have suggested a putative tumor suppressor role for lysyl oxidase because it is downregulated in many human and oncogene-induce d tumors. To address this issue we down-regulated the enzyme in normal rat kidney fibroblasts by stable transfection of its cDNA in an antisense orien tation. The selected clones revealed an absence of lysyl oxidase and dramat ic phenotypic changes, interpretable as signs of transformation. The antise nse lysyl oxidase clones showed, indeed, loose attachment to the plate and anchorage-independent growth and were highly tumorigenic in nude mice. More over, we found an impaired response of the PDGF and IGF-1 receptors to thei r ligands. In particular, the transformed cells showed a down-regulation of both PDGF receptors and expressed the 105-kDa isoform of the IGF-1 beta re ceptor, which was not present in the normal control cells. The lack of resp onse to PDGF-BB has been described as a feature of many ras-transformed phe notypes. Therefore, we looked at the status of the p21(ras). Indeed, we fou nd a significantly higher level of active p21(ras) both during steady-state growth and prolonged starvation. Our data reveal new evidence for a tumor suppressor activity of lysyl oxidase, highlighting its particular role in c ontrolling Ras activation and growth factor dependence.