CONSTITUTIVE OVER-EXPRESSION OF TRANSFORMING GROWTH-FACTOR-ALPHA IN RAT-LIVER EPITHELIAL-CELLS LEADS TO INCREASED CELL CYCLING WITHOUT TRANSFORMATION

Over-expression of transforming growth factor-alpha (TGF-alpha) is con sistently seen in spontaneous transformants of rat liver derived epith elial cells (RLE phi 13) and has been implicated in the transformation of other cultured cells. me have constitutively over-expressed TGF-al pha in RLE phi 13 cells, which are known to express epidermal growth f actor receptors, to determine if TGF-alpha over-expression plays a rol e in transformation or differentiation: or both, of these cells. Early passage RLE phi 13 cells were infected with a replication-defective m urine retrovirus that expresses both the full length coding sequence f or human TGF-alpha and the neomycin-resistance gene. Integration of th e transcriptionally active provirus and expression of TGF-alpha mRNA w ere confirmed. Neither morphologic transformation nor molecular eviden ce for differentiation was noted in TGF-alpha-producing clones. Howeve r, these clones did exhibit an accelerated growth rate, increased expr ession of several cell cycle related genes including mitotic cyclic B- 1, proliferating cell nuclear antigen, c-myc, and p53 as well as incre ased expression of the preneoplastic marker enzyme, glutathione-S-tran sferase. This suggests that over-expression of TGF-alpha results in in creased cell cycling, and that subsequent events must be necessary for cellular transformation or differentiation or both.