AN ISOFORM OF THE HUMAN CALCITONIN RECEPTOR IS EXPRESSED IN TT CELLS AND IN MEDULLARY CARCINOMA OF THE THYROID

We amplified, using the polymerase chain reaction and calcitonin recep tor (CTR) specific primers, RNA extracted from medullary thyroid carci noma (MTC) and the derived TT cell line. Both secrete large amounts of calcitonin. Electrophoresis of amplification products revealed, in bo th cases, an ethidium bromide-stained band that hybridized to a CTR pr obe. Sequencing the band amplified from TT cells revealed an open read ing frame identical to the sequence of H-CTR but lacking 16 amino acid s in the first intracellular loop. This demonstrates the existence of an mRNA coding for a subtype of H-CTR which is expressed in TT cells a nd MTC.