/-sis oncogene-induced transformation of human fibroblasts into cells capable of forming benign tumors

Abstract

Normal human fibroblasts do not synthesize platelet-derived growth factor (PDGF), but they respond to its mitogenic action. In contrast, cells from several human fibrosarcomas have been shown to synthesize PDGF at significant levels. To investigate the possible role of PDGF expression in the development of tumors of mesenchymal origin in humans, we transfected a plasmid carrying the v-sis oncogene and a selectable marker into an infinite lifespan, non-tumorigenic human fibroblast cell strain, MSU-1.1. The v-sis gene codes for a protein homolog of PDGF-B. Of the six independent drug-resistant transfectants clonally isolated, three expressed a relatively low level of v-sis mRNA and protein, grew to a saturation density only 2-2.5 times higher than MSU-1.1 cells, did not form colonies in agar, were not growth factor independent and did not form tumors. The other three expressed v-sis mRNA and protein at a high level, grew to a very high saturation density (> 750,000 cells/cm2), replicated in medium lacking exogenous growth factors almost as rapidly as with 10% serum, formed large colonies in 0.33% agarose and, when injected into athymic mice, formed tumors that grew rapidly. Tumors that were removed after 6 weeks were classified as benign (fibromas). However, several of the tumors that were left in the animals for 6 months developed focal areas of cells showing features of poorly differentiated spindle cell or round cell sarcomas. Similarly, cells isolated from a very large sized agarose colony formed by one of the other v-sis strains expressed very high levels of v-sis mRNA and protein and formed large, very fast growing benign tumors. Re-injection of cells from the tumors yielded tumors composed of two distinct areas: spindle cell fibromas and high grade sarcomas. These results suggest that if mesenchymal cells in the body were induced to express their PDGF-B gene, this could lead to the formation of benign tumors of mesenchymal origin. The system described can serve as a model for studying the mechanisms of formation of such tumors in humans and their progression to the malignant state.

A Novel Human Gene Similar to the Protein Kinase (PK) Coding Domain of the Large Subunit of Herpes Simplex Virus Type 2 Ribonucleotide Reductase (ICP10) Codes for a Serine-Threonine PK and Is Expressed in Melanoma Cells

“…Additionally, cloning was determined at an early passage, before cells with a H11-unrelated growth advantage could be selected. The cloning efficiency of cells transformed with H11 was comparable or greater than that of such oncogenes as v-fos (0.1-0.7% (44)), int-2 (0.35%), c-Ha-ras (0.5%), c-erb B2 (1.0% (45)), and v-sis (2.9 -4.3% (46)) in human cells, suggesting that H11 has a relatively strong transforming activity, as previously reported for ICP10 PK (9 -11). When colonies similar in size to those scored for c-erb B2 and v-sis (60 -80 m) were counted, the cloning efficiency of H11-transformed cells was 10 -20-fold higher than that reported for these oncogenes.…”

Malignant transformation of human fibroblast strain MSU‐1.1 by v‐fes requires an additional genetic change

“…To ascertain that suitable conditions for amplification were present for each sample and to correct for the small differences in the amount of sample added to each reaction tube, the cDNA of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene in each sample was also amplified simultaneously. The primers used for the v-sis and GAPDH genes have been published (Yang et al, 1994). The products were run on 2% agarose gels and the gels were stained with ethidium bromide.…”

“…To determine whether the v-sis oncogene could supply the change required by the v-fes oncogene in malignant transformation of MSU-1.1 cells, we transfected the v-fes oncogene into a non-tumorigenic cell strain, designated MSU-l.l:sisA, that expresses the v-sis oncogene, i.e., carries a cDNA copy of the simian c-sis/PDGF-B gene transcribed from a simian-sarcoma-virus LTR promoter. The non-tumorigenic MSU-1.l:sisA strain had been obtained previously by transfecting the parental MSU-1.1 cells with a plasmid carrying the v-sis oncogene and the gpt gene, and selecting for drug resistance (Yang et al, 1994). The strain expresses the v-sis oncogene, but is not tumorigenic.…”