Malignant Transformation of Human Fibroblasts Caused by Expression Of

Proc. Nati. Acad. Sci. USA Vol. 86, pp. 187-191, January 1989 Cell Biology Malignant transformation of human fibroblasts caused by expression of a transfected T24 HRAS oncogene (human cell transformation/infinite life-span human flbroblasts/pHO6T1/T24 HRAS expression/malignant fibrosarcoma) PETER J. HURLIN*, VERONICA M. MAHER, AND J. JUSTIN MCCORMICKt Carcinogenesis Laboratory, Fee Hall, Department of Microbiology and Department of Biochemistry, Michigan State University, East Lansing, MI 48824-1316 Communicated by G. N. Wogan, September 19, 1988 ABSTRACT We showed previously that diploid human passage rodent cells were transfected with an HRAS onco- fibroblasts that express a transfected HRAS oncogene from the gene and any one of a number of genes considered to be human bladder carcinoma cell line T24 exhibit several char- involved in causing cellular immortalization, malignant trans- acteristics of transformed cells but do not acquire an infinite formation resulted (5-7). Not surprisingly, transfection of life-span and are not tumorigenic. To extend these studies ofthe HRAS oncogenes into infinite life-span rodent fibroblast cell T24 HRAS in human cells, we have utilized an infinite life-span, lines resulted in malignant transformation (5, 8) in the but otherwise phenotypically normal, human fibroblast cell majority of the studies (9). strain, MSU-1.1, developed in this laboratory after transfec- To test models proposed for ras transformation generated tion of diploid fibroblasts with a viral v-myc oncogene. Trans- from experiments with rodent fibroblasts for their relevance fection of MSU-1.1 cells with the T24 HRAS flanked by two to human cell transformation, we and our colleagues (10-12) transcriptional enhancer elements (pHO6T1) yielded foci of and several other groups (13-21) have used human fibroblasts morphologically transformed cells. No such transformation as target cells for transfection of HRAS or NRAS oncogenes occurred if the plasmid containing T24 HRAS had only one or for infection with the Harvey or Kirsten murine sarcoma enhancer or none at all or if the normal human HRAS gene was viruses. Two groups (14, 15, 17) reported that early-passage transfected in the pHO6 vector (pHO6N1). Cell strains derived diploid human fibroblasts are resistant to transformation by from such foci expressed high levels ofT24 HRAS product p21, transfected HRAS oncogenes. However, Hurlin et al. (10) formed colonies in soft at showed that if such cells are transfected with the pHO6T1 agar high frequency, proliferated plasmid, which contains the human T24 HRAS oncogene rapidly in serum-free medium that does not support growth of flanked by Moloney murine sarcoma virus long terminal the parental cell line, and formed progressively growing, repeat and simian virus 40 (SV40) transcriptional enhancer invasive fibrosarcomas. These foci-derived T24 HRAS- sequences in order to increase expression of this gene, they transformed cell strains, as well as cells from the tumors become morphologically transformed, develop distinct foci, derived from them, had the same near-diploid karyotype as and form colonies in soft agar. In a similar study, Tubo and that of the parental MSU-1.1 cells. Transfection of pHO6T1 Rheinwald (20) showed that diploid human fibroblasts trans- into two other inflnite life-span human fibroblast cell lines, cells fected with the T24 HRAS oncogene in a plasmid that that had not been transfected with v-myc, also resulted in contains a SV40 transcriptional enhancer sequence become malignant transformation, suggesting that the infinite life-span morphologically transformed and exhibit reduced growth- phenotype of MSU-1.1 cells, and not necessarily expression of factor requirements. As discussed by Hurlin et al. (10), the the v-myc oncogene, was the factor that complemented T24 negative results referred to above (14, 15 17) most probably HRAS expression to cause malignant transformation. reflect lack of expression of the transfected HRAS oncogene or expression at a level too low to cause measurable effects. Oncogenes of the ras family have been detected in numerous In the positive studies (10, 20), where expression of the and diverse human malignancies (1). A growing body of transfected T24 HRAS oncogene was higher than that of the evidence from both in vivo and in vitro studies suggests that normal HRAS gene, the transformants exhibited several the p21 products ofras oncogenes are involved in the genesis characteristics of tumor-derived cells but did not acquire an of such malignancies. For example, transgenic mice harbor- infinite life-span or tumorigenicity. ing the HRAS oncogene of the human bladder carcinoma cell The majority of the studies of the transforming ability of line T24 (2) or the v-Ha-ras oncogene of Harvey murine oncogenes carried out in rodent cells in culture have used sarcoma virus (3), linked to a promoter specific for expres- fibroblasts that have acquired an infinite life-span in culture sion in mammary tissue, developed mammary tumors. How- but are otherwise apparently normal. Until now, no compa- ever, they did so only after a long latency, and the tumors rable human cell lines have been available for use in testing were clonal in origin, suggesting that additional changes at the applicability of the results of such studies to human the cellular level were required to cause tumor formation. fibroblasts. The few infinite life-span, nontumorigenic human Clues to the nature of the steps or events that may comple- fibroblast cell lines that exist have been generated by using ment mutational activation ofras genes in tumorigenesis have SV40 (22) or repeated exposure to carcinogen (23, 24) and come primarily from in vitro experiments utilizing rodent consist of cells that are morphologically transformed and fibroblasts in culture (for a review, see ref. 1). For example, exhibit other transformed characteristics. Recently, a human when primary or early-passage rodent fibroblasts with a finite fibroblast cell strain with an infinite life-span, designated life-span in culture were transfected with an HRAS onco- MSU-1.1, was generated in this laboratory after transfection gene, no transformation was seen, but when cells that had of foreskin-derived, normal diploid human fibroblasts with a acquired an infinite life-span were used, fully transformed plasmid carrying a v-myc oncogene. These cells, which have cells were obtained (4). Similarly, when primary or early- Abbreviation: SV40, simian virus 40. The publication costs of this article were defrayed in part by page charge *Present address: Fred Hutchinson Cancer Research Center, M616, payment. This article must therefore be hereby marked "advertisement" 1124 Columbia Street, Seattle, WA 98104. in accordance with 18 U.S.C. §1734 solely to indicate this fact. tTo whom reprint requests should be addressed. 187 Downloaded by guest on October 1, 2021 188 Cell Biology: Hurlin et al. Proc. Natl. Acad. Sci. USA 86 (1989) a normal morphology and have exhibited the same near- were labeled with [35S]methionine (New England Nuclear) at diploid karyotype for more than 200 population doublings 250 uCi (1 uCi = 37 kBq) per ml for 18 hr in McM medium postcrisis, do not form foci or produce colonies in soft agar lacking methionine but supplemented with 1% fetal bovine and are nontumorigenic. (A full description of the generation serum. Cell lysis, immunoprecipitation with the ras (any of this cell strain and its properties will be published else- species) p21-specific antibody Y13-259 (33), NaDodSO4/ where.) Using these cells, we have determined that trans- PAGE, and fluorography were performed as described (10). fection of the T24 HRAS oncogene in the pHO6T1 plasmid For analysis of v-myc-encoded p110, cells were labeled as into human cells with an infinite life-span causes them to above, but for only 1.5 hr. Cells were washed in ice-cold exhibit not only the characteristics previously seen with finite phosphate-buffered saline, lysed in lysis buffer (10 mM life-span cells (10) but also the ability to form rapidly growing, Tris HCl, pH 8.2/150 mM NaCl/1% sodium deoxycholate/ malignant fibrosarcomas in athymic mice. 1% Triton X-100/0.1% NaDodSO4/5 mM EDTA/2 mM phenylmethanosulfonyl fluoride), and clarified by centrifu- METHODS AND MATERIALS gation at 10,000 X g for 20 min. Supernatants containing 7.5 Cells and Culture Conditions. Cell line LG1, from which the x 107 cpm were immunoprecipitated with a sheep antibody MSU-1.1 cell strain arose, was initiated from foreskin mate- (Cambridge Research Biochemicals, Valley Stream, NY; rial of a clinically normal newborn male as described (25). antibody OA-11-801) that reacts broadly with the proteins of The MSU-1.1 cell line, described above, is resistant to G418 the myc family. Protein A-Sepharose (Pharmacia) coated (GIBCO) because the plasmid used to transfect the LG1 cells with goat anti-sheep IgG (Cooper Biomedicals, Malvern, PA) carried the aminoglycoside phosphotransferase gene. The was added, and the mixture was shaken for 30 min at 4°C. The infinite life-span human fibroblast cell lines KMST-6 and Sepharose fraction was washed twice with lysis buffer, once SUSM-1, generated after repeated carcinogen treatment (23, with 10 mM Tris HCI, pH 7.5/1 M MgCl2, and again with lysis 24), were obtained from M. Namba. The SV40-transformed buffer. NaDodSO4/PAGE sample buffer containing 8 M urea infinite-life-span cell line GM0637B was purchased from the was added, and the samples were heated for 5 min at 95°C and National Institute of General Medical Sciences (Human centrifuged. Aliquots of the supernatant, along with pre- Genetic Mutant Cell Repository, Camden, NJ). The human stained molecular weight markers (Bethesda Research Lab- bladder carcinoma cell line T24 was purchased from the oratories) were electrophoresed (34) in NaDodSO4/10% American Type Culture Collection, and the chicken hepa- polyacrylamide gels, and the gels were fixed, treated with toma, MC29 virus-producer cell line LSCC-DU72, was enhancer, dried, and exposed to x-ray film as described.

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