DRP, A NOVEL PROTEIN EXPRESSED AT HIGH CELL-DENSITY BUT NOT DURING GROWTH ARREST

Contact is a vital mechanism used by cells to interact with their envi ronment. Contact with living and nonliving elements adjacent to a cell is the basis for many common biological events ranging from growth re gulation to metastasis to embryonic pattern formation. We describe the cloning and characterization of a novel density-regulated protein (dr p) whose expression is increased in cultured cells at high density com pared with cells at low density. A drp cDNA was isolated from the huma n teratocarcinoma cell line PA-1. Northern analysis with a drp probe r evealed transcripts of 2.8 and 3.2 kb. The drp RNA was expressed in a variety of tissues, with the highest amounts in skeletal and cardiac m uscle. Using antipeptide antisera, increasing amounts of a 70-kDa prot ein were detected using several experimental approaches in several cel ls lines as cell density is increased. Conditioned medium from high-de nsity cells was unable to induce expression of drp in cells growing at low density. Similarly, growth arrest by serum starvation or transfor ming growth factor-beta (TGF-beta) treatment failed to elicit drp expr ession. We conclude that drp is a novel protein whose expression is in creased at high cell density but not growth arrest.