Hyperactive autocrine loop mediated by a NDF-related factor in neoplastic hamster embryo fibroblasts expressing an activated cph oncogene.
We described previously the characterization of a novel oncogene, cph, activated in primary Syrian hamster embryo fibroblasts by exposure to 3-methylcholanthrene (Velasco et al., Oncogene 9:2065-2069, 1994). The present report describes the participation in the neoplastic conversion of cph-expressing (81C39) hamster fibroblasts of a hyperactive autocrine loop involving a neu differentiation factor [NDF]-like protein. The tyrosine phosphorylation of the p185erbB-2 receptor in the human breast carcinoma MDA-MB-453 cells was stimulated by conditioned medium from neoplastic 81C39 cells. The extent of this stimulatory effect was much greater than that induced by conditioned medium from normal 84-3 hamster cells. The p185erbB-2 tyrosine phosphorylation-stimulating activity was partially blocked by the heparin analogue pentosan polysulfate [PPS], a known antagonist of p185erbB-2 ligands, and was partially purified from 81C39 conditioned medium by heparin-Sepharose chromatography. The level of p185erbB-2 tyrosine phosphorylation-stimulating activity in the heparin-Sepharose fractions correlated directly with their content in NDF-like protein as immunodetected with an anti-rat NDF antibody. Consistently, the steady-state level of NDF-related mRNA was found to be four times greater in neoplastic 81C39 cells than in normal 84-3 cells. However, the levels of erbB-2 mRNA were similar in both cell types, while the expression of erbB-4 mRNA was upregulated in the neoplastic fibroblasts. The ability of 81C39 conditioned medium to stimulate protein tyrosine phosphorylation and to induce other PPS-sensitive growth responses on 81C39 cells themselves suggested the involvement of an autocrine loop in their neoplastic conversion. The participation of a NDF-related factor in this autocrine loop was confirmed by the ability of an anti-NDF antibody to block the mitogenic activity present in their own conditioned medium. The involvement of the cph oncogene in the upregulation of NDF-related expression was evidenced when cph-transformed NIH3T3 fibroblasts showed elevated levels of NDF-related mRNA, and their conditioned medium induced tyrosine phosphorylation on MDA-MB-453 cells, reproducing the effect of the medium from 81C39 hamster cells.
Avila
M A
MA
Department of Radiation Medicine, Georgetown University Medical Center, Washington, DC 20007.
Velasco
J A
JA
Cho
C
C
Lupu
R
R
Wen
D
D
Notario
V
V
D016475:3T3 Cells; D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D006224:Cricetinae; D005347:Fibroblasts; D006023:Glycoproteins / Q000502:physiology*; D051379:Mice; D020880:Neuregulins; D009857:Oncogenes; D019000:Phosphotyrosine; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
D006023:Glycoproteins; D020880:Neuregulins; D019000:Phosphotyrosine; D018719:Erb-b2 Receptor Tyrosine Kinases; D014443:Tyrosine