DIFFERENTIAL EXPRESSION OF THYROGLOBULIN GENE IN NORMAL AND TRANSFORMED THYROID-CELLS

The synthesis of thyroglobulin was measured in 2 differentiated cell lines, FRTL-5 and FRTL-424, and 2 transformed thyroid cell lines, FRA and 1-5G. The untransformed cells actively synthesized and exported thyroglobulin in the medium: the FRTL-5 cell line synthesized 7 times less thyroglobulin than the FRTL-424 cell line, even though both cell types contained equal amounts of functional thyroglobulin mRNA. In contrast the transformed cells expressed extremely low levels of thyroglobulin mRNA, even though there was no detectable change in gene structure or copy number as determined by Southern blot analysis. Apparently, the different levels of thyroglobulin synthesis in the 2 untransformed cell lines are due to stable post-transcriptional alterations in the biosynthesis of thyroglobulin and the transformation of thyroid cells results in a substantial reduction in thyroglobulin gene expression.