Immortalization of human endothelial cells by murine sarcoma viruses, without morphologic transformation

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Abstract
Amphotropic murine leukemia virus pseudotypes of murine sarcoma viruses containing theras or mos oncogenes were constructed to permit efficient introduction of the sarcoma virus genome into early‐passage human umbilical vein endothelial cells. The resulting cell lines were morphologically and phenotypically unchanged, retaining properties characteristic of differentiated endothelial cells. For example, the cells in a Kirsten sarcoma virus‐modified line were found to biosvnthesize and secrete von Willebrand factor in both a constitutive and regulated manner, and they contained ultrastructurally identifiable Weibel‐Palade bodies, an endothelial cell‐specific organelle. In contrast to the parent cultures, sarcoma virus‐modified cells were able to proliferate indefinitely in culture. Examination of both Kirsten sarcoma and Moloney leukemia virus‐modified lines indicated that the immortalized cells retained a diploid female karyotype after over 18 months in culture. In addition, the sarcoma virus‐modified cells were able to grow independently of added endothelial cell growth factor. This growth factor autonomy does not appear to be due to autocrine production of a biologically cross‐reactive growth factor. These immortal, virus‐modified endothelial cells express large amounts of sarcoma virus‐specific mRNA but no detectable helper virus or transforming virus activity. This technique for immortalization of primary human cells without alteration of the differentiated characteristics of the cell type is readily applied to a variety of human cell types. Moreover, the ability to separate the immortalizing and transforming activities of viral oncogenes should provide further understanding as to mechanisms of oncogene action.