The thrust of this study is to elucidate the genetic mechanisms of neoplastic transformation of normal tissues and the cellular immune defense mechanisms against neoplastic cells. Two experimental systems were used: 1) A human oncogene derived from a hepatocellular carcinoma currently established in tissue culture; 2) T-cell growth factor, an autocrine of T-cells, and CCDF (cytotoxic cell differentiation factor), produced by macrophages for the induction of natural killer cells to become cytotoxic cells. A systematic screening with DNA transfection assay, preferential AFB-1 binding and repeated molecular clonings were carried out and led to the successful isolation of a human oncogene, PM-1, capable of cell transformation and its cell transformation capability was enhanced by more than 300 fold upon AFB-1 activation. PM-1 was 3.1 kb and shared some homology with the ras oncogene. We have done a restriction map of PM-1 and have also resolved the nucleotide sequence of approximately 65% of the entire gene; the latter verified the accuracy of the restriction sites along the genome. We also pinpointed some of the deoxyguanine targets in the PM-1 nucleotide sequence under controlled binding conditions with AFB-1 epoxide, yielding some relevant information regarding nucleotide sequence specificity influencing carcinogen activation of an oncogene. After extensive purification, the function and relationship of two oncogene products, IL-2 and CCDF, after extensive purification have been resolved. In the absence of antigenic or mitogenic stimulation, IL-2 provides the first signal to activate the cytotoxic precursors and prepares these cells to differentiate into cytotoxic effectors in the absolute presence of CCDF. The sequential actions of these two lymphokines are critical for the generation of lymphokine-induced cytotoxicity, a cellular process considered pivotal in cellular immune defense mechanisms against tumor cells.
