Biological assay for activity and molecular mechanism of retinoids in cervical tumor cells

The composition and response of the retinoid signaling pathway in a human cell line (CC-1), representative of a low grade cervical carcinoma, were evaluated. Reverse-transcriptase polymerase chain reaction (RT-PCR) analysis demonstrated expression of cytoplasmic retinol binding protein, CRBPI, cytoplasmic retinoic acid binding protein, CRABPII, and nuclear retinoic acid receptors, RAR alpha, RARgamma, RXR alpha, and RXRbeta, but not CRABPI or RARbeta. This pattern is similar to that of the ectocervix. Activation of endogenous nuclear receptors was evaluated in a reporter subline of CC-1, called CC-B, containing a reporter gene controlled by a retinoic acid responsive element (RARE) and thymidine kinase promoter. Retinoid treatment of CC-B resulted in dose-dependent increases in reporter gene expression. Retinoids inhibited growth at concentrations greater than 100 nM. 9-cis retinoic acid (1 nM) significantly stimulated growth. Immunohistochemical analysis of CC-B organotypic cultures demonstrated a high level of epidermal growth factor receptor (EGF-R) expression that was decreased by retinoids. The degree of RARE transactivation induced by retinoids significantly correlated with the degree of inhibition of growth (R = -0.96) and EGF-R expression (R = -0.92). The dose-dependent and retinoid-specific responses of CC-1 at the molecular and biological levels demonstrate the utility of this reporter cell line for evaluation of retinoid activities.