A Novel RET Kinase–β-Catenin Signaling Pathway Contributes to Tumorigenesis in Thyroid Carcinoma

Abstract

The RET receptor tyrosine kinase has essential roles in cell survival, differentiation, and proliferation. Oncogenic activation of RET causes the cancer syndrome multiple endocrine neoplasia type 2 (MEN 2) and is a frequent event in sporadic thyroid carcinomas. However, the molecular mechanisms underlying RET's potent transforming and mitogenic signals are still not clear. Here, we show that nuclear localization of Bcatenin is frequent in both thyroid tumors and their metastases from MEN 2 patients, suggesting a novel mechanism of RET-mediated function through the B-catenin signaling pathway. We show that RET binds to, and tyrosine phosphorylates, B-catenin and show that the interaction between RET and B-catenin can be direct and independent of cytoplasmic kinases, such as SRC. As a result of RETmediated tyrosine phosphorylation, B-catenin escapes cytosolic down-regulation by the adenomatous polyposis coli/ Axin/glycogen synthase kinase-3 complex and accumulates in the nucleus, where it can stimulate B-catenin-specific transcriptional programs in a RET-dependent fashion. We show that down-regulation of B-catenin activity decreases RET-mediated cell proliferation, colony formation, and tumor growth in nude mice. Together, our data show that a Bcatenin-RET kinase pathway is a critical contributor to the development and metastasis of human thyroid carcinoma.

Transcript Level Modulates the Inherent Oncogenicity of RET/PTC Oncoproteins

“…Janne Balsamo and Jack Lilien and was obtained from the Development Studies Hybridoma Bank, developed by the National Institute of Child Health and Human Development, and maintained at the University of Iowa. Full-length wildtype RET, RET K758M, and GFRa1 constructs have been described previously (14). Empty vector (EV) refers to pcDNA3.1 plasmid (Invitrogen).…”

“…HeLa cells were fixed and stained as described previously (14). Individual images were obtained with a Leica TCS-SP2 inverted microscope.…”

Signaling pathways in follicular cell-derived thyroid carcinomas

“…Another dysfunctional signaling pathway identified in 65-90% of RET/PTC-positive tumors is β-catenin, which is involved in gene transcription and cell adhesion regulation (60,61). The β-catenin pathway can be directly activated by several mechanisms: via RET tyrosine residue, cAMP response element-binding (CREB), glycogen synthase kinase 3 phosphorylation (GSK3-S) or via effectors of the MAPK and PI3K pathways (61,62).…”

“…The β-catenin pathway can be directly activated by several mechanisms: via RET tyrosine residue, cAMP response element-binding (CREB), glycogen synthase kinase 3 phosphorylation (GSK3-S) or via effectors of the MAPK and PI3K pathways (61,62). The increase in the free β-catenin protein pool promotes proliferation and invasion, possibly due to the interaction with transcriptional factors, such as the T-cell factor/ lymphoid enhancer factor (TCF/LEF), c-Myc (v-myc myelocytomatosis viral oncogene homolog), or cyclin D1 (60,61,63).…”

RET-mediated modulation of tumor microenvironment and immune response in multiple endocrine neoplasia type 2 (MEN2)

“…Activated RET, including RET MEN2, can activate the Wnt pathway, that inhibits the recruitment of antigenpresenting cells (i.e., dendritic cells) (Gujral et al 2008, Castellone et al 2009, Prazeres et al 2011, Tartari et al 2011. Interestingly, it has been shown that an immune response could be elicited in MTC patients by vaccination with tumor cell-pulsed autologous dendritic cells, indicating that MTC cells display antigens that could activate antigen-presenting cells.…”