Abstract
Βeta-catenin is a protein functioning in cell adhesion which also acts as a nuclear effector of Wnt signalling, where it associates with the DNA-binding proteins TCF/LEF. These complexes activate the expression of genes involved in cell proliferation, transformation and intercellular adhesion. NrCAM, a cell adhesion molecule found primarily in the nervous system, was recently shown to be overexpressed in papillary thyroid carcinomas (PTC).
To examine whether Wnt signalling plays a role in regulating NrCAM expression we analyzed NrCAM, β-catenin and cyclin D1 gene and protein expression in a series (38) of PTC and paired normal tissues (NT) using Q-RT-PCR, immunochemistry and Western blot methods.
Q-RT-PCR analysis showed a clear increase in the abundance of RNA transcripts encoding NrCAM, β-catenin and cyclin D1 in thyroid carcinomas compared to normal tissue (P < 0.0001). NrCAM mRNA levels were significantly correlated with expression of the β-catenin (R = 0.79, P < 0.0001) and cyclin D1 (R = 0.60, P < 0.0001) genes in tumours, but not in NT. Using a panel of tissue samples from different thyroid carcinoma patients, low or negligible NrCAM levels were detected by immunohistochemistry (IHC) in NT, whereas 78% (53/68) of PTC showed strong immunostaining for this protein. Western blot data validated the Q-RT-PCR and IHC NrCAM results. Immunohistochemically, β-catenin was observed in three distinct subcellular locations and all tumours showed overexpression of nuclear cyclin D1. Strong positive immunostaining for NrCAM was highly significantly correlated with cytoplasmic β-catenin translocation (P < 0.0029). Upregulation of NrCAM, β-catenin and cyclin D1 expression at both the mRNA and protein levels was seen regardless of the primary tumour stage (pT) or size.
Our findings indicate the involvement of Wnt/β-catenin signalling in NrCAM gene activation in PTC.
This work was supported by CMKP grant 501-1-1-22-01/07.