MCM3 Protein Expression in Follicular and Classical Variants of Papillary Thyroid Carcinoma

Minichromosome maintenance (MCM) proteins are needed as licensors in the DNA replication of eukaryotic cells and transcriptional control of MCM genes has critical role in the regulation of MCM functions. Different MCM protein family members are proposed as diagnostic or prognostic markers in various cancers due to their increased proliferative potential. Among MCM family members, minichromosome maintenance protein 3 (MCM3) expressions in both mRNA and protein levels were shown to be associated with papillary thyroid carcinoma (PTC). But, the usability of MCM3 in some histological variants of PTC might be controversial due to tissue specific molecular heterogeneities. In follicular variant of papillary thyroid carcinoma (FVPTC), a number of genes including MCM3 were shown to be differentially expressed which were specific to this kind of variant. Using immunohistochemistry method, MCM3 protein expression levels were compared in FVPTC, classic variant of papillary thyroid carcinoma (CVPTC), and multi-nodular goiter (MNG) tissues in a group of 32 cases. There was meaningful differences between MNG vs. FVPTC (p = 0.016) and MNG vs. CVPTC (p = 0.019) while there was no significant difference in the comparison FVPTC vs. CVPTC (p = 0.15). Four of the 5 CVPTC cases having surrounding tissue invasion had high expression values. For FVPTC and CVPTC, MCM3 protein expression results were parallel to our previous mRNA expression study while there was downregulation in protein expression despite the increased expression of MCM3 mRNA in MNG suggesting tissue-specific post-transcriptional events in benign thyroid neoplasms of which should be focused on. Moreover, the relatively lower MCM3 protein expression in FVPTC comparing to CVPTC could be due to a different tumorigenic pathway favored in this type of tissue.