Bloom syndrome fibroblasts secrete a metabolite which enhances SCE rate in normal fibroblasts

We can corroborate the findings of Tice and colleagues (Nature 273:538-540, 1978) of increased frequency of sister chromatid exchange (SCE) in normal skin fibroblasts upon cocultivation with Bloom syndrome (BS) fibroblasts. In addition, we have demonstrated that conditioned media from BS fibroblasts also increase the SCE frequency of normal cells. The results suggest that Bloom syndrome fibroblasts synthesize an altered metabolite that is capable of increasing the frequency of sister chromatid exchange in normal fibroblasts. The nature of this factor remains obscure, but it is likely to involve the DNA replication process. Sister chromatid exchange is a DNA synthesis-dependent phenomenon, and its dramatic alteration of Bloom syndrome cells may indicate a defect in a protein engaged in semiconservative DNA replication.