Nerve growth factor synthesized by mouse fibroblast cells in culture: absence of alpha and gamma subunits.

Nerve growth factor (NGF) is found in high concentrations in the mouse salivary gland. However, this gland is unique since salivary glands from other animals have only trace amounts of NGF. In the mouse gland, two high molecular weight forms of NGF have been reported, 7S-NGF [Varon, S., Nomura, J., & Shooter, E.M. (1967) Biochemistry 6, 2202-2209] and NGF1 [Young, M., Saide, J.D., Murphy, R.A., & Blanchard, M.H. (1978) Biochemistry 17, 1490-1498]. 7S-NGF is comprised of three noncovalently associated subunits: beta-NGF, which is the biologically active subunit, alpha subunit, and gamma subunit. A similar subunit composition is seen with NGF1 (unpublished work with R.A. Murphy). Since the mouse salivary gland is unique with regard to its synthesis of NGF, the following question arises. Do other sources of NGF produce either 7S-NGF or NGF1? Mouse fibroblast cells (L929) in culture synthesize and secrete into their feeding medium (conditioned medium) a beta-NGF-like molecule [Pantazis, N.J., Blanchard, M.H., Arnason, B.G.W., & Young, M. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 1492-1496]. These cells therefore provided the opportunity to examine the molecular nature of NGF produced by a nonsalivary gland source. In this study, it was determined by radioimmunoassay that neither the alpha nor the gamma subunit is present in fibroblast cell conditioned medium. Since alpha- and gamma-proteins are present in both 7S-NGF and NGF1, this indicates that neither of the salivary gland forms of NGF are produced by the mouse fibroblast cell.