Transformation of human epidermal keratinocytes with fission neutrons

The biological effects of exposures to high LET radiations haveparticular relevance to radiation protection and risk assessmentSince most cancers are of epithelial origin, it is importantto obtain a better understanding of radiationinduced oncogenictransformation in this cell type. Accordingly we have initiatedstudies to determine whether immortalized human epidermal keratinocytes(RHEK) can be transformed with high LET radiations. Exponentiallygrowing RHEK cells were treated with single doses (1, 10, 25,50 and 100 cGy) of 0.85 MeV fission neutrons from the Janusreactor. Neutron exposure led to the development of morphologicallyaltered cells and foci formation after 6 weeks at confluence.These transformed cultures grew with an increased saturationdensity, exhibited anchorageindependent growth and formed tumorshi athymlc mice. Single-strand conformatlonal polymorphism analysisand DNA sequencing demonstrated the absence of point mutationsin codons 12/13 and 61 in the Ha-ras, Ki-ras, or N-ras genesand exons 4–9 of the pS3 tumor suppressor gene. Thesestudies demonstrate that high LET radiations (fission neutrons)can transform immortalized human epithelial cells to a malignantphenotype that does notappear to involve mutations in eitherthe cellular p53 or ras genes.