title: Intranuclear dynamics of DNA polymerase alpha differs between the transplanted R3230AC mammary adenocarcinomas and the host mammary gland depending on lactation cycle.
abstract: DNA polymerase alpha activity was markedly higher in all nuclear subfractions, including nuclear matrix, from transplanted R3230AC mammary adenocarcinomas than in the analogous fractions from mammary gland of same tumor-bearing pregnant or lactating rats. Changes in host lactational status had no significant effect on subnuclear distribution of tumor DNA polymerase alpha activity, with the majority (60-75%) localized in soluble nucleoplasm and a significant amount (13-20%) retained in the nuclear matrix. In the host mammary gland, nuclear matrix-bound DNA polymerase alpha was highest, accounting for 48% of total nuclear activity, during late pregnancy when mammary cells undergo rapid raplication. During lactation, when cells in mammary gland cease to divide, only 8% of enzyme activity was in the nuclear matrix, while the majority (60-80%) of DNA polymerase alpha activity was localized in nucleoplasm. In both R3230AC tumor and mammary gland regardless of host's lactational status, the majority (60-80%) of DNA polymerase beta activity was localized in the high salt-soluble chromatin. These present data thus suggest that, regardless of host lactational status, R3230AC tumor has many cycling cells, each with a large pool of DNA polymerase alpha molecules maintaining maximal and constant replicative activity, while normal mammary gland cells have a smaller pool of DNA polymerase alpha which become primarily matrix-bound only during active cell replication during late pregnancy. A constant localization of nuclear DNA polymerase beta in chromatin in both mammary gland and the tumor suggest it is not important in mammary cell proliferation.
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology*; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology*; D004256:DNA Polymerase I / Q000378:metabolism; D004257:DNA Polymerase II / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism; D005260:Female; D007774:Lactation / Q000502:physiology*; D008325:Mammary Neoplasms, Experimental / Q000201:enzymology*; D009368:Neoplasm Transplantation; D011247:Pregnancy; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D004273:DNA, Neoplasm; D004256:DNA Polymerase I; D004257:DNA Polymerase II