Transforming growth factor-beta 1 (TGF beta 1) enhances apoptosis in human papillomavirus type 16-immortalized human ectocervical epithelial cells

Transforming growth factor beta (TGF beta) is a potent inhibitor of epithelial cell growth. In the present study TGF beta 1 modulation of human ectocervical epithelial cell growth and differentiation is evaluated using an HPV16-immortalized human ectocervical cell line, ECE16-1. These cells were found to contain a high-affinity receptor for TGF beta 1 (Kd = 75 pM). TGF beta (10-500 pg/ml) suppressed ECE16-1 growth and [3H]thymidine incorporation in a dose-dependent manner. Growth inhibition was reversible at TGF beta 1 concentrations of 100 pg/ml or less. At higher concentrations of TGF beta 1, treatment for longer than 2 days induced irreversible growth inhibition. In addition to its effects on cell growth, TGF beta 1 treatment increased apoptosis in ECE16-1 cells as measured by an increase in cornified envelope formation, flow cytometry, and DNA fragmentation. Apoptosis was enhanced at doses > or = 100 pg/ml. There was a highly significant increase in the activity of tissue transglutaminase, an enzyme believed to play an important role in apoptosis. This increase in transglutaminase activity was paralleled by a TGF beta 1-stimulated increase in fibronectin levels. Transglutaminase and fibronectin have been shown to associate during tissue remodeling. These data suggest that TGF beta 1 may act as an important paracrine/autocrine factor to stimulate normal cervical remodeling and to limit HPV16-immortalized cervical cell progression by stimulating apoptosis. The induction of fibronectin and tissue transglutaminase suggests that the TGF beta 1 pathway of cell death differs from that of normal ectocervical epithelial cell differentiation, which is mediated by epidermal transglutaminase.