No abstract

Abstract. We have investigated the roles of pp60-src and p21-proteins in transducing the nerve growth factor (NGF) and fibroblast growth factor (FGF) signals which promote the sympathetic neuronlike phenotype in PC12 cells. Neutralizing antibodies directed against either Src or Ras proteins were microinjected into fused PC12 cells. Each antibody both prevented and reversed NGF-or FGF-induced neurite growth, a prominent morphological marker for the neuronal phenotype . These data demonstrate the involvement of both pp60--and p21--proteins in NGF and FGF actions in PC12 cells, and establish a physiological role for the pp60c-s-tyrosine kinase in signal transduction pathways initiated by receptor tyrosine kinases in these cells . Additional microinjection experiments, N ERVE growth factor (NGF)l (39) and fibroblast growth factor (FGF) (for review see reference 70) are neuronal growth factors which mediate survival and differentiation ofmany types ofneurons in vivo and in primary neuronal cultures. Application ofNGF or FGF to cells ofthe clonal rat pheochromocytoma cell line, PC12, engages a program ofphysiological changes, resulting in a phenotype resembling that of sympathetic neurons . These changes include neurite outgrowth, establishment ofa sodium-based action potential, induction of a variety ofbiochemically defined neuronal characteristics, and the cessation of cell division (see reference 18) . The PC12 cell line has thus been a useful model system for studying the intracellular events associated with growth factor-induced neuronal differentiation .The signal transduction pathways used by NGF to accomplish these changes have been extensively studied but are only partially understood. Underlying the physiological changes brought about by NGF and FGF is a coordinated sequence of posttranslational modifications and changes in gene expression that occur throughout persistent treatment with the growth factor (for review see reference 23) . Several 1. Abbreviations used in this paper: FGF, fibroblast growth factor ; GAP, GTPase activating protein ; MMTV, mouse mammary tumor virus; NGF, nerve growth factor. © The Rockefeller University Press, 0021-9525/91/11/809/11 $2.00 TheJournal of Cell Biology, Volume 115, Number 3, November 1991809-819 using PC12 transfectants containing inducible v-src or ras oncogene activities, demonstrated a specific sequence of Src and Ras actions . Microinjection of antiRas antibody blocked v-src-induced neurite growth, but microinjection of anti-Src antibodies had no effect on ras oncogene-induced neurite growth . We propose that a cascade of Src and Ras actions, with Src acting first, is a significant feature of the signal transduction pathways for NGF and FGF The Src -Ras cascade may define a functional cassette in the signal transduction pathways used by growth factors and other ligands whose receptors have diverse structures and whose range of actions on various cell types include mitogenesis and differentiation . second messenger pathways have been implicated in NGF action includi...

In adult animals, sensory neurons innervating the skin are phenotypically diverse. We have now investigated whether nerve growth factor (NGF) has a physiological role in the development of this diversity. We gave antisera against NGF to rats from postnatal day 1 (PND 1) to adulthood (5 weeks). We found a virtually complete depletion of high threshold mechanoreceptors conducting in the A delta range (2-13 ms-1) in the sural nerve. This afferent type, normally present in large numbers, appeared to have been replaced by D-hair afferents, sensitive mechanoreceptors which normally are relatively rare. NGF deprivation had this effect only in early postnatal life; treatment from postnatal day 14 to adulthood had no effect. We conclude that the presence of NGF postnatally in skin is necessary for the proper phenotypic development of A delta cutaneous nociceptors.