Cell‐surface expression of glia maturation factor β in astrocytes

Glia maturation factor β (GMF‐β) is a 17‐kDa acidic protein isolated from the brain. When added to cultured cells, GMF‐β promotes the phenotypic expression of glia and neurons and inhibits the proliferation of their respective tumors. Although astrocytes produce GMF‐β and store it inside the cells, they do not secrete the protein into the cultured medium. This poses a question as to how GMF‐β mediates intercellular communication. This paper provides an answer by demonstrating the presence of GMF‐β on the surface of astrocytes, using gold‐labeled antibody enhanced with silver. It appears that cell‐surface GMF‐β acts on the target cells at close range when cells are in direct contact. In contrast to astrocytes, we failed to detect GMF‐β on the surface of C6 glioma cells, although these cells, like astrocytes, possess endogenous intracellular GMF‐β and are also responsive to GMF‐β added to the medium. The lack of cell‐surface expression of GMF‐β in C6 cells may reflect a breakdown in intercellular communication in these malignant cells.—Lim, R.; Liu, Y.; Zaheer, A. Cell‐surface expression of glia maturation factor β in astrocytes. FASEB J. 4: 3360–3363; 1990.