Anoxia, wound healing, VL30 elements, and the molecular basis of malignant conversion

Although VL30 retrotransposable elements have been associated with certain cancers for nearly twenty years, because of their expression in rodent malignancies and recombination into murine sarcoma viruses, their causative role, if any, in cancer has been uncertain and enigmatic. Recent findings suggest loss of normal transcriptional control of specific VL30 element expression may make a critical contribution to tumor progression at a step associated with malignant conversion, by bringing into play a cellular program normally involved in wound healing. This program, the fibroblast anoxic response system, includes an adaptation to glycolytic metabolism, secretion of metalloproteinases, and activation of an endonuclease. While appropriate for facilitating debris removal during wound healing, loss of control of this program in a cell which has already progressed to the benign neoplastic state has the potential to simultaneously produce the invasiveness and genomic instability charateristic of malignancy. Examination of tumors and tumor derived cell lines has confirmed that key aspects of this system are in fact activated in cancer.