Immunohistochemical detection, regulation and antiproliferative function of G-protein-coupled receptor kinase 2 in thyroid carcinomas

Abstract

TSH, via its G-protein-coupled receptor, activates cell growth of both benign and malignant thyroid tumors. G-proteincoupled receptors (GR) kinase 2 (GRK2) has been reported to regulate the TSH receptor but its role in cancer is unknown. To determine a possible function for GRK2 in the growth process of thyroid cancers, we analysed its expression in normal and tumoral thyroid tissues and studied thyroid cancer cell line proliferation after GRK2 overexpression. Thirty one thyroid tissues, including 16 non-medullary thyroid cancers and 15 adjacent normal tissues, were analysed by immunohistochemistry. Five paired tissues were also studied by western blotting for the GRK2 enzymatic activity. Immunohistochemical staining showed an increase in GRK2 in thyroid cancers including papillary, follicular, and anaplastic types, compared with their adjacent normal tissues. Immunoblot analysis and GRK2 enzymatic activity measurement confirmed immunohistochemical study. TSH and TSH in association with insulin or IGF-I stimulated GRK2 protein accumulation in normal human thyroid cells in primary culture. The TSH effect on the GRK2 expression was mimicked by forskolin. After GRK2 overexpression in two poorly differentiated thyroid cell lines, all the clones showed a significant reduction in cell proliferation, ranging from 28 to 65% inhibition compared with vector alone after 96-h culture. In conclusion, thyroid mitogenic factor-stimulated GRK2 accumulation may explain, in part, high GRK2 levels in differentiated carcinoma, because TSH, insulin, or IGF-I is known to be involved in the thyroid cancer progression. Surprisingly, instead of stimulating, GRK2 reduced cell proliferation revealing a new role for this kinase in the growth of thyroid cancers.

Link between Cancer and Alzheimer Disease via Oxidative Stress Induced by Nitric Oxide-Dependent Mitochondrial DNA Overproliferation and Deletion

“…It is known that altered GRK2 expression levels modulate chemokines-mediated induction of MEK/ERK activity through both kinase-dependent and -independent function [48] and its aberrant epithelial cell motility that plays a key role in cancer progression and metastasis (Figure 1). GRK2 protein levels have been differentially upregulated in tissue samples of patients with granulose cell tumors, with differentiated thyroid carcinoma [49, 50] or downregulated in a subgroup of prostate tumors [51], which suggests that altered GRK2 expression in specific tumor cells may affect migration in response to particular stimuli and plays a critical role in basic cellular functions such as cell proliferation, differentiation or migration during development. Further, GRK2 inhibits TGF-mediated cell growth arrest and apoptosis in human hepatocarcinoma cells [46].…”

“…Further, GRK2 inhibits TGF-mediated cell growth arrest and apoptosis in human hepatocarcinoma cells [46]. On the other hand, GRK2 attenuates serum- or PDGF-induced proliferation of thyroid cancer cell lines [49] and smooth muscle cells [43], whereas its expression increases MAPK signaling in response to EGF in HEK-293 cells [52] and GRK2 kinase activity is required for IGF-1-triggered proliferation and mitogenic signaling in osteoblasts [53] (Figures 1 and 2). …”

Inhibition of G-protein-coupled Receptor Kinase 2 (GRK2) Triggers the Growth-promoting Mitogen-activated Protein Kinase (MAPK) Pathway

“…Because growth-regulatory pathways are essential for cardiomyocyte survival (16,17), we considered the impact of GRK2 inhibition on cell growth and proliferation. However, the role of GRK2 in cell growth and proliferation is not clear, because in addition to the above mentioned growth-promoting activity, GRK2 can also exert growth inhibition leading to suppressed growth and proliferation of tumor cells (18,19).…”

G protein–coupled receptor kinase 2 (GRK2) modulation and cell cycle progression

“…GRK2 inhibits TGFmediated cell growth arrest and apoptosis in human hepatocarcinoma cells (4). On the other hand, GRK2 attenuates thyroid stimulating hormone-and PDGF-dependent proliferation of thyroid cancer cell lines (5) and smooth muscle cells (6), respectively, whereas it increases mitogenic signaling pathways in response to EGF in osteoblasts (7) or upon activation of the Smoothened receptor in fibroblasts (8). Increased GRK2 levels also potentiate migration of epithelial cells toward fibronectin and sphingosine-1-phosphate (9).…”