The biological effects of retinoic acid (RA) are mediated by nuclear retinoic acid receptors (RARs) that function as ligand-activated transcriptional factors. The response of human cancer cells to RA is known to be associated with the expression of RARbeta. Recent studies have demonstrated that the loss of RARbeta expression is involved in the development of a variety of human malignancies. We show that recombinant adenovirus-mediated p21(sdi1) gene transfer enhances RARbeta mRNA expression as well as protein expression and induces the sensitivity to all-trans RA (ATRA) in human cancer cells. Semi-quantitative reverse transcription-polymerase chain reaction analysis demonstrated that infection with adenovirus carrying human p21(sdi1) gene (Ad5CMV-p21), which encodes a cyclin-dependent kinase inhibitor, induced RARbeta mRNA and protein expression in H1299 human non-small cell lung cancer cells and DLD-1 human colorectal cancer cells. We also found that exogenous introduction of the p21(sdi1) gene transcriptionally activated the upstream promoter function of the RARbeta gene. Treatment with 1 microM of ATRA showed no significant inhibitory effects on the growth of H1299 and DLD-1 cells; after Ad5CMV-p21 infection, however, cells underwent apoptosis with ATRA treatment at the same concentration, suggesting that p21(sdi1) gene transfer sensitized H1299 and DLD-1 cells, presumably, through RARbeta upregulation. We also demonstrated the efficacy of intratumoral injection of Ad5CMV-p21 in combination with systemic administration of ATRA in a nude mice xenograft model. Our results indicate that recombinant adenovirus-mediated p21(sdi1) gene transfer could be potentially useful for the local induction of RA sensitivity in human premalignant and malignant lesions lacking appropriate RARbeta expression.
Copyright 2002 Wiley-Liss, Inc.