Modulation by retinoic acid (RA) of squamous cell differentiation, cellular RA-binding proteins, and nuclear RA receptors in human head and neck squamous cell carcinoma cell lines.

The ability of all-trans-retinoic acid (RA) to modulate the growth and squamous differentiation of four head and neck squamous cell carcinoma cell lines (183, 886, 1483, and SqCC/Y1) was examined, and the relationship of their state of squamous differentiation and RA responsiveness to the expression of cytosolic RA-binding proteins (CRABPs), nuclear RA receptors (RARs), and retinoid X receptors (RXRs) was investigated. RA inhibited proliferation of all but the 183 cell line and suppressed squamous differentiation markers K1 keratin, type 1 transglutaminase, and involucrin mRNAs and proteins to varying degrees in 183, 1483, and SqCC/Y1 cells. Traces of CRABP-I mRNA were detected only in the 886 cells, whereas CRABP-II mRNA was detected in the other three cell lines. RA suppressed CRABP-II expression in SqCC/Y1 cells but had no effect on its expression in the other cell lines. All cell lines expressed mRNAs for RAR-alpha, RAR-beta, RAR-gamma, and RXR-alpha. The RAR-beta mRNA level was lowest in the SqCC/Y1 cells, and RXR-beta and RXR-gamma were not detected in any of the cell lines. RA treatment increased the levels of the three RAR mRNAs in most of the cell lines but had no effect on the RXR mRNAs. The CRABP-II mRNA level in SqCC/Y1 cells was lowest in cells grown in serum-free medium and increased when the cells were grown in medium with 5 or 10% serum. In contrast, the RXR-alpha mRNA level was inversely related to serum concentration. The results show that, in head and neck squamous cell carcinoma cells, there are no simple relationships among the expression of CRABPs, RARs, and RXRs and either squamous differentiation or response to RA-induced growth inhibition or suppression of squamous differentiation.