Deregulated Alternative Splicing of CD44 Messenger RNA Transcripts in Neoplastic and Nonneoplastic Lesions of the Human Thyroid¹

CD44 is a polymorphic family of immunologically related cell surface proteoglycans and glycoproteins implicated in cell-cell and cell-matrix adhesion interactions, lymphocyte activation and homing, cell migration, and tumor metastasis. CD44 exists as a standard form and as multiple isoforms, each generated by alternative splicing of up to 10 variant exons (termed v1–v10) encoding parts of the extracellular domain. Using semiquantitative reverse transcriptase-PCR and Southern hybridization, alternative CD44 mRNA splicing was examined in 10 papillary thyroid carcinomas, 8 nodular goiters, 9 adenomas, 2 cases of thyroiditis, and 3 histologically normal thyroid controls. The amount of input cDNA for the CD44 PCRs was standardized against an internal control gene (glyceraldehyde phosphate dehydrogenase). Four papillary carcinomas showed significant overexpression of CD44 transcripts migrating between 750 and 1000 bp. These cases demonstrated reduced levels of the 482-bp standard isoform transcript. In six papillary cancers, we found a prominent v6-containing isoform at 750 bp that was present in only trace amounts in normal thyroid tissue. It is of interest that similar findings were seen in the majority of the goiters and adenomas but not in the cases of thyroiditis. These results show that deregulation of alternative CD44 splicing is a common feature of disordered thyroid follicular cell growth, both in neoplastic and nonneoplastic lesions. The data imply an important role for CD44, including CD44v6, in the pathogenesis of various thyroid lesions.