Milk-Specific RNase as a Marker of Differentiation of Rat Mammary Tumors

Abstract

Abstract

Various rat mammary tumors were analyzed for the presence of a milk-specific Ca²⁺-stimulated RNase (Ca²⁺-RNase). When crude extracts of some differentiated tumors—adenocarcinomas of MT/W9, MT/W9a, R3230AC, DMBA-1, DMBA-8, and DMBA-14 and 3MN squamous cell carcinoma—were assayed for RNase activity under various ionic conditions, it was always highest in the presence of Ca²⁺/EDTA than under any other ionic condition. The opposite was true in invasive MT/W449a and 13762 adenocarcinomas, poorly differentiated SMT/2A carcinomas, MAMF₂/TC fibrosarcoma, and MT/A fibroadenoma. Sephacryl S-200 chromatography separation of tumor extracts confirmed the presence of Ca²⁺-RNase in those differentiated tumors and absence of the enzyme from other tumors. Expressing the activity as a ratio of Ca²⁺/EDTA to either Mg²⁺/EDTA or EDTA alone to more clearly represent the relative level of Ca²⁺-RNase activity further illustrates the distinct differences between tumor classes. Thus Ca²⁺-RNase is a sensitive marker for use in the characterization of rat tumors with respect to differentiated mammary functions.