CHARACTERIZATION AND GROWTH-DEPENDENT REGULATION OF THE NERVE GROWTH-FACTOR RECEPTOR GP140(TRK) IN RAT C6 GLIOMA-CELLS

The glioma cell line C6 was used to study the expression and growth-de pendent regulation of the nerve growth factor (NGF) tyrosine kinase re ceptor gp140(trk), which is the mature protein product of the trk prot o-oncogene. Chemical cross-linking of I-125-NGF to C6 cells, followed by immunoprecipitation with polyclonal anti-NGF antibodies and separat ion by polyacrylamide gel electrophoresis, revealed the presence of 90 -95 and 150 kDa species. Immunocytochemical staining of C6 cells with antibodies directed against either the low-affinity NGF receptor gp75( NGFR) or trk proto-oncogene products demonstrated a heterogeneous cell ular distribution of both antigens. Brief treatment of C6 cells with N GF led to the tyrosine phosphorylation of 80, 110 and 140 kDa protein species, as detected on anti-phosphotyrosine Western blots. Similar mo lecular weight species were found with anti-Trk antibodies in the NGF- treated cells. Intracellular localization of Trk-like immunoreactivity in C6 cells released from a growth-arrested state indicated an initia l immunostaining of the nuclear periphery, progressing to cytoplasmic vesicles and finally to the plasma membrane. These observations at the light microscopic level were confirmed using immunoelectron microscop y with the same anti-Trk antibodies, and showed clearly the traffickin g of Trk-like immunostained particles from the endoplasmic reticulum t o the plasmalemma. The cellular localization of trk gene products also appeared to depend on their glycosylation state. Such growth-dependen t expression of NGF receptors on glial cells may be important in contr olling autocrine regulatory processes of glia to NGF, which these cell s produce.