Functional Thyrotropin Receptor Attenuates Malignant Phenotype of Follicular Thyroid Cancer Cells

Abstract

Thyrotropin (TSH) is a thyroid-specific growth factor inducing differentiated function and growth of thyrocytes in vitro. In thyroid cancer, loss of TSH-receptor (TSHR) expression is a sign of de-differentiation and is believed to contribute to the malignant phenotype. The present studies aimed to determine the in vitro and in vivo effects of functioning TSHR in the follicular thyroid cancer cell line HTC, a subclone of FTC133 cells, lacking endogenous expression of TSHR, and HTCtshr+ cells transfected with human TSHR-cDNA. HTCtshr+ cells grew faster in vitro (doubling time 1.15 vs 1.56 d, p < 0.05) and TSH caused a dose-dependent growth response. Adhesion to and invasion through reconstituted basement membrane were reduced in HTCtshr+ cells, but when stimulated with TSH increased to levels comparable to naïve HTC cells. In vivo, tumor latency was 11 d for naïve HTC as compared to 21 d for HTCtshr+ xenografts. Smaller tumor volumes were registered for HTCtshr+ cells (250 +/- 217 vs 869 +/- 427 mm3, p < 0.05). Angiogenesis, as determined by vascular surface density (VSD) of experimental tumors, was enhanced in naïve HTC tumors (VSD 0.87 +/- 0.1 microm-1 vs 0.55 +/- 0.2 microm-1 in HTCtshr+, p < 0.05). VEGF secretion was more pronounced in naïve HTC cells stimulated with EGF, than in HTCtshr+ cells stimulated with either TSH or EGF. In conclusion, regained expression of functional TSHR in the follicular thyroid cancer cell line HTC alters in vitro features commonly associated with the malignant phenotype. Smaller tumors and reduced angiogenesis of xenotransplanted HTC cells with functioning TSHR suggest a less aggressive in vivo phenotype. The present data highlight the pivotal role of TSHR to affect transformed thyrocytes in vitro and in vivo. They also suggest a role for EGF as a modulator of angiogenesis in thyrocytes devoid of TSHR.

Epidermal growth factor receptor overexpression is a marker for adverse pathologic features in papillary thyroid carcinoma

“…demonstrated that papillary thyroid carcinomas (PTCs) express EGFR, and PTCs overexpress EGFR during dedifferentiation or anaplastic transformation (5). EGFR overexpression (EGFR-H) is described in anaplastic thyroid carcinomas (ATCs) (6), follicular thyroid carcinomas (FTCs) (7, 8) and in primary medullary carcinomas (MTC), despite the absence of identifiable somatic EGFR mutations (9, 10). …”

TSH signalling and cancer

“…The importance of the TSHR signalling for the onset/evolution of thyroid cancer is supported by experiments in which regained expression of functional TSHR in a follicular thyroid cancer cell line (HTC) reduced angiogenesis and size of tumours of xenotransplanted HTC cells (16). Hyperactivated TSHR is commonly found in most adenomas, less common in differentiated carcinomas and the gene is silenced in undifferentiated cancers such as ATC (table 1, see also figure 1).…”

Emerging therapeutics for advanced thyroid malignancies: rationale and targeted approaches

“…Therapies which target the TSH pathway by mechanisms other than inducing TSH suppression with levothyroxine have not yet been brought to the clinic, yet may hold promise. For example, loss of the TSH receptor (TSH-R loss) has been associated with a more aggressive DTC phenotype - and TSH-R reconstitution has been shown to slow DTC cell line growth in vitro and in vivo , 14 thereby providing preliminary preclinical evidence supporting the future clinical translation of this approach.…”