Insulin-like growth factor binding protein-3 does not mediate the interferon-dependent suppression of human ectocervical epithelial cell proliferation

Interferon is a potential therapeutic agent for the treatment of cervical cancer. In the present study we examine the role of IFNγ as a regulator of proliferation and production of IGFBP-3 expression in ectocervical epithelial cells. ECE16-1 cells are a model for studying early human papillomavirus-dependent cervical disease. IFNγ produces a concentration-dependent inhibition of ECE16-1 cell proliferation that is associated with an increase in insulin-like growth factor binding protein-3 level. Growth suppression and IGFBP-3 increase is maximal at concentrations of IFNγ ≥0.75 ng/ml. The increased IGFBP-3 expression is mediated via an increase in IGFBP-3 encoding mRNA. In contrast, IFNγ inhibits proliferation of CaSki and SiHa cells, but IGFBP-3 is barely detectable and levels are not regulated by IFNγ. These results suggest that the IFNγ-dependent suppression of CaSki and SiHa cell proliferation is not mediated by secreted IGFBP-3. This result was confirmed when vector-mediated overexpression of immunoreactive IGFBP-3 in SiHa and CaSki cells did not consistently result in reduced cell proliferation rate.