RNA directed DNA polymerase activity in retinoblastoma: report of its presence and possible significance

RNA directed DNA polymerase is a recently discovered enzyme which catalyzes the synthesis of DNA using RNA as a template in the reversal of the usual mode of passage of genetic information. This enzyme has received great attention because of its reported presence in all of the animal RNA tumor viruses analyzed. Utilizing the current methods of identification of the enzyme, RNA directed DNA polymerase type activity was found to be present in ten specimens of retinoblastoma. This enzyme activity was also found in medulloblastoma and neuroblastoma. This appears to be the first demonstration of an RNA directed DNA polymerase activity in a human ocular tumor. This enzyme was not demonstrated in ocular tissues, brain or adrenal gland, in a variety of other malignant tumors, including lymphomas and sarcomas, or in certain rapidly dividing tissue culture cell lines. Additional control studies were carried out using avian myeloblastosis virus and feline sarcoma and lymphoma virus and experimental retinal tumors induced with feline sarcoma virus in cats. The biochemical activity of the viral enzyme in these materials corresponded closely to that in the human tumors.