Enhanced expression of a 27 kD protein during diethylnitrosamine-induced hepatocarcinogenesis in rats

Patterns of neosynthesized cellular proteins from normal rat liver and from diethylnitrosamine-induced neoplastic nodules and hepatocellular carcinomas were analyzed by radiolabeling and fluorography of two-dimensional gel electrophoregrams. Three proteins exhibited a significant and reproducible increase in labeling intensity in the nodules (n = 5) and in the tumors (n = 10) as compared to the normal liver (n = 10). Two of those proteins (MW 31 and 33 kD, pI of 5.25, 5.15 respectively) are secreted proteins and as yet, we have no clue as to their nature. The third one is an intracellular protein of 27 kD pI 5.5. Several similarities in physico-chemical properties (MW, pI, phosphorylated state, low methionine content) indicate that this 27 kD protein might be the 27 kD heat shock protein (27 HSP). This is further supported by our observation that the cadmium-induced 27 HSP comigrates with our 27 kD protein.