Nicholas J. Pantazis

Epidermal growth factor and nerve growth factor in mouse saliva: A comparative study

It has recently been determined (Murphyet al., 1977a) that the submandibular gland of the adult mouse is an exocrine rather than endocrine organ for nerve growth factor (NGF). Present results, together with the work of others, suggest the gland is serving the same function with respect to epidermal growth factor (EGF). Radioimmunoassay data indicate that EGF is secreted in saliva at concentrations which are similar to that of NGF. Highest levels of the molecules are present in saliva from male mice stimulated with α-adrenergic and β-adrenergic secretagogues. A cholinergic agonist elicits saliva containing appreciably lower amounts of both proteins. Saliva EGF stimulates division of epithelial cells in chick cornea grown in culture, suggesting that the molecule is secreted in a form which is biologically active. Chemical studies indicate that the molecular properties of saliva EGF vary depending upon the concentration at which the molecule is studied. In concentrated saliva, EGF elutes from gel filtration columns in a position which suggests the protein is part of a high molecular weight complex. At levels where EGF is biologically activein vitro, however, the complex dissociates and EGF displays a molecular weight close to 6000 g/mole in dilute solution. This behavior is identical to that of EGF in salivary gland extracts. Saliva NGF, on the other hand, remains in a high molecular weight form when studied at biologically effective levels.

Secretion of a nerve growth factor by mouse neuroblastoma cells in culture

Analyses of supernatant solutions from mouse C1300 neuroblastoma cultures by two independent immunoassays reveal that these cells secrete a factor which is immunochemically similar to mouse submaxillary gland nerve growth factor. The neuroblastoma factor is also biologically active in inducing neurite outgrowth from embryonic sensory ganglia-an effect that is completely blocked by specific antibody to nerve growth factor. Neuroblastoma cells are known to be functionally responsive to nerve growth factor, and the observation that they secrete a molecule like it may mean that these cells require or utilize the factor during growth in culture.

Studies on the Molecular Properties of Nerve Growth Factor and its Cellular Biosynthesis and Secretion

In the preceding chapter, Bradshaw et al. have summarized much of the historical background information arising from the discovery of and early studies on nerve growth factor (NGF) by Bueker and by Levi-Montalcini, Hamburger and their colleagues. Here we should only like to draw attention to a brief list of those historical aspects which are most pertinent to the studies to be presented below. 1. NGF was first discovered as a soluble diffusible factor present in 2 mouse sarcomas. This factor has never been isolated and purified, and thus its chemical properties are unknown. 2. Male adult mouse submandibular glands contain large amounts of NGF, whose covalent structure is known, and male glands contain much more than female glands. 3. Little, if any, NGF is present in the glands of newborn mice--a perplexing observation since the factor is believed to play a central role in the embryonic development of the autonomic and sensory nervous systems. 4. Removal of mouse submandibular glands appears to have no obvious deleterious effect upon the animal—and NGF has not been detected in the salivary glands of other mammals. 5. Treatment of newborn mice with antibody to NGF results in selective destruction of the sympathetic nervous system without other obvious pathologic changes. 6. Small amounts of a nerve growth-promoting activity have been found in experimentally-induced granulation tissue, serum, and many peripheral tissues—for reasons unknown.