High level expression of p27(kip1) and cyclin D1 in some human breast cancer cells: inverse correlation between the expression of p27(kip1) and degree of malignancy in human breast and colorectal cancers.

The expression of cyclin-dependent kinase inhibitor p27(kip1) in human tumors and normal tissues was investigated using a panel of novel anti-p27(kip1) mAbs. An inverse correlation between expression of p27(kip1) and cell proliferation was generally observed after analyzing its expression in 25 different normal human tissues. In some highly proliferative human breast cancer cells, however, high level p27(kip1) expression was seen, indicating the existence of a mechanism by which some growing tumor cells may tolerate this inhibitor of cell cycle progression. Detailed studies demonstrated a correlation between the high level expression of p27(kip1) and cyclin D1 in human breast cancer cells. There was also an inverse correlation between the expression of p27(kip1) and the degree of tumor malignancy in human breast and colorectal cancers, indicating that p27(kip1) may be a useful prognostic marker in these cancers.

Isolation of cDNA clones encoding an enzyme from bovine cells that repairs oxidative DNA damage in vitro: homology with bacterial repair enzymes.

Ionizing radiation and radiomimetic compounds, such as hydrogen peroxide and bleomycin, generate DNA strand breaks with fragmented deoxyribose 3' termini via the formation of oxygen-derived free radicals. These fragmented sugars require removal by enzymes with 3' phosphodiesterase activity before DNA synthesis can proceed. An enzyme that reactivates bleomycin-damaged DNA to a substrate for Klenow polymerase has been purified from calf thymus. The enzyme, which has a Mr of 38,000 on SDS-PAGE, also reactivates hydrogen peroxide-damaged DNA and has an associated apurinic/apyrimidinic (AP) endonuclease activity. The N-terminal amino acid sequence of the purified protein matches that reported previously for a calf thymus enzyme purified on the basis of AP endonuclease activity. Degenerate oligonucleotide primers based on this sequence were used in the polymerase chain reaction to generate from a bovine cDNA library a fragment specific for the 5' end of the coding sequence. Using this cDNA fragment as a probe, several clones containing 1.35 kb cDNA inserts were isolated and the complete nucleotide sequence of one of these determined. This revealed an 0.95 kb open reading frame which would encode a polypeptide of Mr 35,500 and with a N-terminal sequence matching that determined experimentally. The predicted amino acid sequence shows strong homology with the sequences of two bacterial enzymes that repair oxidative DNA damage, ExoA protein of S. pneumoniae and exonuclease III of E. coli.