Beneficial effects of retinoic acid on extracellular matrix degradation and attachment behaviour in follicular thyroid carcinoma cell lines

The prognosis of patients with metastasised follicular thyroid carcinoma (F TC) is limited, necessitating the search for new treatment options. Benefic ial effects of retinoids have been suggested in thyroid cancer and the pres ent study was performed to investigate the effects of retinoic acid (RA) on important determinants of metastatic behaviour in FTC: the disengagement o f tumour cells from the primary tumour and the degradation of extracellular matrix, focusing on the role of the plasmin activation system and the inte grin and E-cadherin families of attachment molecules. Three FTC cell lines were studied: FTC-133, derived from the primary tumour; and FTC-236 and FTC -238, derived from metastases. FTC cell lines were cultured with 0(.)1, 1 a nd 10 muM 13-cis-RA or with the solvent DMSO for 1 and 5 days. Extracellula r matrix degradation by these cell lines was studied by assessing the 48-h release of radioactivity from S-35- methionine labelled extracellular matri x proteins synthesised by the MC3T3 cell line coated onto plastic. The invo lvement of constituents of the plasmin activation system was investigated b y semi-quantitative RT-PCR and zymography. Attachment to extracellular matr ix was studied by determining the number of adhering FTC cells to extracell ular matrix coated onto plastic, 3 h after seeding. The involvement of atta chment molecules was studied by RT-PCR with primers for integrin subclasses and E-cadherin and immunofluorescence for E-cadherin. Five days culturing with 10 muM RA reduced the degradation of extracellular matrix significantl y in all cell lines: FTC-133 by 35%, FTC-236 by 74% and FTC-238 by 31%. Zym ography revealed diminished activity of urokinase type plasminogen activato r (uPA) in FTC-236 and FTC-238, but not in FTC-133 cultured with RA. mRNA e xpression of the uPA receptor was diminished in FTC-236. In the attachment assay, 10 muM RA for 5 days increased the number of adherent cells to extra cellular matrix significantly by 91% in FTC-133, 64% in FTC-236 and 87% in FTC-238. No effects of RA on integrin or E-cadherin mRNA expression were ob served. Immunofluorescence, however, revealed enhanced organisation of E-ca dherin along the cell membrane by RA treatment. In conclusion, the present study demonstrates beneficial effects of RA on important determinants of me tastatic behaviour in FTC cell lines, e.g. decreased degradation of extrace llular matrix which may in part be explained by effects on the plasmin acti vation system and enhanced attachment to extracellular matrix. These findin gs may add to the explanations for beneficial effects of retinoids in thyro id cancer.