RETINOIC ACID INDUCES INTERCELLULAR-ADHESION MOLECULE-1 HYPEREXPRESSION IN HUMAN THYROID-CARCINOMA CELL-LINES

The expression of intercellular adhesion molecule-1 (ICAM-1) in tumora l tissues may promote their interaction with the immune system and cyt otoxic effect on tumoral cells. This observation led to the investigat ion of ICAM-1 expression and modulation in different tumoral cell syst ems in vitro. Recently, retinoic acid-responsive elements have been fo und in the 5'-regulatory region of the human ICAM-1 gene. In the prese nt study, we investigated, by flow cytometry, the effect of retinoic a cid on the surface expression of ICAM-1 in human thyroid carcinoma cel l lines. Two papillary (NPA and TPC-1), one follicular (WRO), one anap lastic (ARO) and one immortalized fetal (TAD-2) cell Line have been st udied. All of them produced constitutively ICAM-1; its surface express ion and specific messenger ribonucleic acid (mRNA) levels were increas ed significantly by retinoic acid in all except the WRO cell line. ICA M-1 hyperexpression by retinoic acid was time dependent, reversible, a nd dependent on mRNA and protein synthesis. Furthermore, cytokines, su ch as interferon-gamma and tumor necrosis factor-alpha, both individua lly and, to a greater extent, in combination with retinoic acid, incre ased ICAM-1 surface expression and its mRNA levels. In conclusion, ret inoic acid is able to induce ICAM-1 up-regulation via mRNA accumulatio n in human thyroid carcinoma cell lines.