Molecular cloning of cDNAs corresponding to mRNAs whchi increase in malignantly transformer FRTL cells.

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We previously developed malignantly transformed cells designated as FRTL-Tc with thyroid stimulating hormone (TSH) receptors which were derived from FRTL cells. To characterize these FRTL-Tc cells further, we cloned cDNAs corresponding to mRNA species showing increased expression in FRTL-Tc cells compared to FRTL cells. A lambda gt10 library was constructed using polyadenylated mRNA from FRTL-Tc cells. The library was then screened for the cDNAs by differential plaque filter hybridization using single stranded cDNA probes synthesized from mRNA prepared from FRTL and FRTL-Tc cells. Of 25, 000 clones screened, 3 clones (Cl3, C17 and C140) were found to represent mRNA species whose levels were higher in FRTL-TC cells.Densitometric quantification of the mRNAs corresponding to C13, C17 and C140 in FRTL-TC cells gave values of 2.84, 1.33 and 5.86, respectively, when the levels in FRTL cells were taken as 1.0. The sizes of C13, C17 and C140 were 1.0, 0.8 kb, respectively. Northern blot analysis showed that the sizes of the corresponding mRNAs to these clones were 1.0, 2.0 and 0.8 kb, respectively. The mRNAs corresponding to C13 and C140 were found in all tissues investigated from Eisher rats, but the expression of C17 MRNA was extremely high in the thyroid only. Determination of the partial nucleotide sequences of these three clones showed they were neither genes for thyroglobulin nor thyroid peroxidase. C17 and C140 bore no homology to any known nucleotide sequences, but C13 was 90% homologous with the human ribosomal protein, Po. Electron microscopy showed that more free ribosomes existed in FRTL-Tc cells than in FRTL cells. Characterization of these genes might provide insights into the novel opportunity to study the nature of thyroid cancer as well as the function of normal thyroid epithelial cells.