Transformation by Ras Suppresses Expression of the Neurotrophic Growth Factor Pleiotrophin

Abstract

An 18-kDa protein (p18) was detected in lysates and conditioned medium from contact-arrested NIH 3T3 fibroblasts, but was not detected when the cells were transformed by the oncogene ras. Analysis of transformation-defective cell clones generated after mutagenesis of the ras-retroviral vector used to transduce the ras gene showed an inverse correlation between p18 expression and the degree of transformation. p18 expression was high in non-transformed clones, intermediate in a partially transformed clone, undetectable in fully transformed clones, and detectable only at the non-permissive temperature in a clone which was cold-sensitive for ras transformation. In non-transformed cells, p18 expression varied with the degree of confluence. It was almost undetectable in medium from sparse, proliferating cells, but increased as the cells approached confluence and peaked 2-4 days after confluence. Microsequencing of partially purified p18 identified it as the developmentally regulated neurotrophic factor pleiotrophin. In further experiments, pleiotrophin was undetectable or almost undetectable in medium from fully transformed cells expressing the oncogenes v-src, truncated c-raf, activated c-fms, or polyomavirus middle tumor antigen; it was low but easily detectable in medium from SV40 large tumor antigen-expressing cells, which form soft agar colonies but not foci. Thus, pleiotrophin expression in NIH 3T3 cells is associated with quiescence, and suppression of pleiotrophin is related to oncogenic transformation.

Pleiotrophin, an angiogenic and mitogenic growth factor, is expressed in human gliomas

“…1b). In lysates from U343 glioma cells and cells from WHO grade IV gliomas, but not in a grade II glioma, a single band of 18 kDa was detected corresponding to published values (Corbley 1997). …”

“…Mature PTN is a non-glycosylated, lysine-rich peptide that migrates anomalously as an 18-kDa band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) (therefore also termed p18; Corbley 1997) and is derived from a 168-residue precursor with a 32 amino acid signal sequence. PTN is mitogenic for various cell types, it promotes angiogenesis, stimulates neurite outgrowth from cultured neurones, and induces cell migration (Li et al 1990;Fang et al 1992;Delbe et al 1995;Souttou et al 1997Souttou et al , 2001Rauvala et al 2000).…”

Pleiotrophin, a candidate gene for poor tumor vasculature and in vivo neuroblastoma sensitivity to irinotecan

“…This is not the first time that the function of PTN is debated. PTN expression in NIH 3T3 cells was found to be associated with quiescence, and suppression of PTN was found to be related to oncogenic transformation (Corbley, 1997). Furthermore, Nakagawara et al (1995) reported that PTN expression is correlated with a better prognosis in NB.…”

Nitric oxide stimulates migration of human endothelial and prostate cancer cells through up‐regulation of pleiotrophin expression and its receptor protein tyrosine phosphatase β/ζ

“…37 PTN is increased in non-tumor-bearing skin adjacent to excised squamous cell carcinomas 38 and eNOS-transfected oral carcinoma SCC-25 cells have decreased growth rate in vitro and in vivo compared with the wild-type parental or vector control-transfected cells. 39 Over-expression of PTN in NIH 3T3 cells has been implicated in cellular quiescence rather than an oncogenic phenotype 40 and PTN has been identified as a confluence specific protein in several types of cells, 10,40,41 among which endothelial cells. 10 Similarly, activity of eNOS is significantly increased in quiescent compared with growing endothelial cells.…”