Differential display in primary and metastatic medullary thyroid carcinoma

Despite recent advances in the understanding of the role of the RET proto-oncogene in the development of familial and approximately 30% of sporadic medullary thyroid carcinomas (MTC), little is known about other genetic events that modify the course and outcome of the disease. We compared the expression of genes in intrathyroidal MTCs to autologous local lymph node metastases by means of mRNA differential display (DDRT-PCR). This is the first report of differential display using surgical specimens of a primary cancer and its metastases. Total RNA was extracted from tumor tissue of two patients with MTC associated with multiple endocrine neoplasia (MEN 2B) and sporadic MTC, respectively. Following reverse transcription (RT), the products were PCR-amplified and separated on a denaturating polyacrylamide gel. RT-PCR products demonstrating differential expression were reamplified and used as probes for Northern blot analysis. Six fragments for which differential expression was confirmed were cloned and sequenced. Resultant sequences were tested for homology to sequences in public data bases, and two novel MTC-derived fragments (MDF-1, MDF-2) were identified. Sensitivity of the method was confirmed by identification of a sequence encoding the calcitonin precursor flanking peptide which is expressed almost exclusively in MTC and normal thyroid C cells. Overexpression of the ribosomal genes S3a and P0 was found in the metastases. Recent reports suggest that components of the translational apparatus act as regulatory mediators of growth, proliferation, and neoplastic change. The altered expression of ribosomal proteins and gene products encoded by MDF-1 or MDF-2 may play an important role in the progression and metastatic spread of MTC.