Purification and characterization of the DNA polymerase of human breast cancer particles.

Abstract

Previous studies identified human breast tumor particles possessing many features characteristic of RNA tumor viruses. In addition to the expected size (600 S) and density (1.16 g/ml) these include possession of an outer membrane and an inner one surrounding a core containing a DNA polymerase and a large MW (70 S) RNA possessing detectable homology to the RNAs of the mouse mammary tumor virus (MMTV) and Mason-Pfizer monkey virus (MPMV). Purification and characterization of the DNA polymerase from the human breast cancer particles is reported. Its key properties are very similar to those of the RNA-dependent DNA nucleotidyltransferase (reverse transcriptases) found in MMTV and MPMV. Like these viral enzymes, the purified human breast cancer DNA polymerase exhibits 3 features that together distinguish the known viral reverse transcriptases from normal cellular DNA polymerases: a strong preference for oligo(dT).cntdot.poly(rA) over oligo(dT).cntdot.poly(dA) as a template for the synthesis of poly(dT); the acceptance of the highly specific oligo(dG).cntdot.poly(rCm) as a template for the formation of poly(dG); the ability to use a viral RNA (AMV [avian myeloblastosis virus]) as a template to fashion a faithful DNA complementary copy; and its preference for Mg2+ over Mn2+. Data on the human breast cancer particle enzyme indicate similarities to the viral agents associated with the corresponding malignancies in the mouse and monkey models. To date, an enzyme with these properties has not been detected in normal breast tissues or in benign breast tumors.