Transformation of revertant murine cells by 5-azacytidine results in rapid inhibition of lysyl oxidase expression

Lysyl oxidase (LO) is synthesized intracellularly as a proenzyme that is secreted and then processed extracellularly to a mature form. LO is expressed in NIH3T3 cells, but only very low levels are observed after NIH 3T3 is transformed by c-H-ras or one of several other oncogenes. LO functions as a tumor suppressor. Treatment of ras-transformed cells with interferon-α with or without retinoic acid results in their persistent reversion to a non-transformed state that is dependent on the restoration of LO expression. When such revertant cells are treated with 5-azacytidine (5-azaC), they undergo rapid morphological retransformation. Within one passage after addition of 5-azaC, there was a down regulation of LO mRNA and proenzyme protein. These data suggest a direct relationship between the transformed state and LO expression.