SPECIFIC IMMUNOSTAINING FOR CCP-II, A NOVEL CALCITONIN CARBOXYL-TERMINAL PEPTIDE ENCODED BY THE CALCITONIN CGRP GENE/

Alternative splicing of the primary transcript of the CALC I gene in t hyroid C-cells results predominantly in calcitonin (CT) mRNA (exons 1- 4), whereas CGRP mRNA (exons 1, 2, 3, 5, and 6) is mainly produced in neuronal cells. The CT mRNA encodes for a protein precursor containing an amino terminal peptide, CT, and a carboxyl terminal peptide (CCP I ). CGRP precursor is composed of the same amino terminal peptide and C GRP. Recently we reported the presence of a third mature transcript of the CALC I gene in human medullary thyroid carcinoma (MTC) tissues. T his transcript encodes for a precursor containing the amino terminal p eptide CT and a novel carboxyl terminal peptide, CCP II. This finding was further confirmed in the TT-cell line derived from a human MTC. We produced monoclonal antibodies against CCP II and developed a rapid a nd specific immunofluorescence method for this peptide. We demonstrate d CCP II-specific immunoreactivity in TT-cells and in MTC tissues. CCP II labeling was relatively homogeneous in contrast to CT and CGRP, wh ich presented striking heterogeneity for intensity of labeling. Theref ore, CCP II mRNA is translated in tumor cells in an apparently constit utive way.