Transforming Growth Factor-β1 (TGFβ1) Enhances Apoptosis in Human Papillomavirus Type 16-Immortalized Human Ectocervical Epithelial Cells

Abstract

Transforming growth factor beta (TGFβ) is a potent inhibitor of epithelial cell growth. In the present study TGFβ1 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 TGFβ1 (Kd = 75 pM). TGFβ (10-500 pg/ml) suppressed ECE16-1 growth and [3H]thymidine incorporation in a dose-dependent manner. Growth inhibition was reversible at TGFβ1 concentrations of 100 pg/ml or less. At higher concentrations of TGFβ1, treatment for longer than 2 days induced irreversible growth inhibition. In addition to its effects on cell growth, TGFβ1 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 ⩾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 TGFβ1-stimulated increase in fibronectin levels. Transglutaminase and fibronectin have been shown to associate during tissue remodeling. These data suggest that TGFβ1 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 TGFβ1 pathway of cell death differs from that of normal ectocervical epithelial cell differentiation, which is mediated by epidermal transglutaminase.