Werner syndrome (WS) results from defects in the gene encoding WRN RecQ helicase. WS fibroblasts undergo premature senescence in culture. Because cellular senescence is a tumor suppressor mechanism, we examined whether WS fibroblasts exhibited reduced tumorigenicity, in comparison to control cells, in a model of experimental conversion of normal human cells to cancer cells. The combination of oncogenic Ras (Ha-RasV12G) and SV40 large T antigen (SV40 LT) causes human cells to acquire neoplastic properties in the absence of telomerase. We found that WS cells could also be converted to a tumorigenic state by these oncogenes, as evidenced by invasion and metastasis of cells implanted in immunodeficient mice. Ras/SV40 LT-expressing cells retained invasiveness and malignant properties even when cells reached crisis in tumors in vivo. High levels of gelatinase were found by an in situ assay in Ras/SV40 LT-expressing cells undergoing crisis. We conclude that, despite evidence of accelerated senescence in WS cells, there is no evidence that the absence of active WRN acts as a barrier to neoplastic transformation. Moreover, we find that tumorigenic human cells retain malignant properties of the cells as they approach and reach crisis.

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