Expression of retinoid-related genes in serum-free cultures of normal, immortalized and malignant human oral keratinocytes

Retinoids are used in the clinical treatment of oral squamous carcinoma, including both early and late stages. Inter-individual variation in responsiveness, including a common insensitivity of advanced stages, suggest that changes in retinoid-related functions might characterize tumor development. To investigate a genetic basis for this hypothesis, an in vitro multi-step model of carcinogenesis involving normal (NOK), SV40 T antigen-immortalized (SVpgC2a) and malignant (SqCC/Y1) oral keratinocytes was analysed under identical culture conditions using micro-array technique (Affymetrix HG_U95A chip) for expression of 52 genes related to retinoid metabolism and actions. The variable detection of between 22-26 transcripts in the cell lines, involving binding/transport factors, receptors, transcriptional activators/repressors and responsive genes, indicated specificity in regards to the expression of known retinoid-related genes in oral keratinocytes. The transformed cell lines variably exhibited differences as compared to NOK, i.e., lower transcript levels for cellular retinol binding protein, the cellular retinoic acid binding protein II (CRABP II) and retinoic acid receptor γ, whereas in contrast, the levels of CRABP I were higher. Transcripts for proteins interacting with nuclear retinoid receptors were similarly expressed among the cell types, whereas transcripts for retinoid-metabolizing enzymes were generally not detected. Finally, transcripts of retinoid-responsive genes, including RARRES3, RI58, NN8-4AG and midkine, were variably expressed. The overall results imply selective expression of retinoid-related functions in normal and transformed keratinocytes, and that cell transformation can impair the capacity for binding and storage of retinol as well as retinoic acid-mediated signalling. These multiple alterations are consistent with possible retinoid insensitivity during oral carcinogenesis.