P1, a high mobility group-like protein is depressed in human breast adenocarcinoma

Protein P1, which is a nuclear protein resembling high mobility group proteins, has been studied in human breast adenocarcinomas and compared to those from control tissue. The presence of the protein was confirmed by in vitro phosphorylation by casein kinase II and immunoblotting, using antibodies raised in rabbits against rat liver P1. The protein has been isolated by reverse phase HPLC chromatography which provides a more rapid method of purification requiring smaller amounts of material. The levels of P1 expression were investigated and it was found that there was a three-fold increase in the ratio of P1/histone H1 in normal breast tissue as compared to the neoplastic tissue. In two other malignant and non-malignant tissues studied, the level of P1 was also decreased in the malignant tissues. Thermolytic phosphopeptides of P1 from normal and malignant human breast tissues exhibited the same pattern, though when compared to the phosphopeptide pattern from rat tissue, differences were observed.