IN-VITRO AND IN-VIVO, ACCELERATION OF THE NEOPLASTIC PHENOTYPE OF A LOW-TUMORIGENICITY RAT BLADDER-CARCINOMA CELL-LINE BY TRANSFECTED TRANSFORMING GROWTH-FACTOR-ALPHA

We conducted an experiment to determine whether expression of transfor ming growth factor-alpha (TGF-alpha) enhances tumorigenicity in a low- tumorigenicity rat bladder carcinoma cell line and whether it is suffi cient to induce a tumorigenic phenotype in a nontumorigenic rat bladde r cell line. D44c cells (which are nontumorigenic) were derived from a minute nodule from a bladder treated with N-methyl-N-nitrosourea (MNU ); G1-200 cl-17 cells (which have low tumorigenicity) were isolated fr om D44c cells exposed to MNU in vitro. Neither cell line expressed TGF -alpha mRNA. The cells were cotransfected with pSV2neo and pSR alpha-r TGF-alpha. The latter plasmid contains the rat TGF-alpha cDNA under th e transcriptional control of the SR alpha promoter. In the low-tumorig enicity G1-200 cl-17 cells, the expression of TGF-alpha mRNA and the s ubsequent synthesis of TGF-alpha protein activated epidermal growth fa ctor receptors (EGFRs) and markedly enhanced tumorigenicity in nude mi ce (i.e., shortened the latency period before tumor appearance, accele rated the rate of growth, and increased the size of the tumors) as wel l as anchorage-independent growth in vitro. In nontumorigenic D44c cel ls, however, transfected TGF-alpha did not induce either anchorage-ind ependent growth or tumorigenicity in nude mice, in spite of overexpres sion of EGFR mRNA and the constitutive expression of c-jun and junB mR NA. These results suggest that the increased signal transduction media ted by TGF-alpha enhanced tumorigenicity in a cell that was already tu morigenic but was not sufficient to induce tumorigenicity in a nontumo rigenic cell. (C) 1994 Wiley-Liss, Inc.