No abstract

Purpose: Oncogenic conversion of BRAF occurs in f44% of papillary thyroid carcinomas and 24% of anaplastic thyroid carcinomas. In papillary thyroid carcinomas, this mutation is associated with an unfavorable clinicopathologic outcome. Our aim was to exploit BRAF as a potential therapeutic target for thyroid carcinoma. Experimental Design: We used RNA interference to evaluate the effect of BRAF knockdown in the human anaplastic thyroid carcinoma cell lines FRO and ARO carrying the BRAF V600E ( V600E BRAF) mutation. We also exploited the effect of BAY 43-9006 [N-(3-trifluoromethyl-4-chlorophenyl)-N'-(4-(2-methylcarbamoyl pyridin-4-yl)oxyphenyl)urea], a multikinase inhibitor able to inhibit RAF family kinases in a panel of six V600E BRAF-positive thyroid carcinoma cell lines and in nude mice bearing ARO cell xenografts. Statistical tests were two sided. Results: Knockdown of BRAF by small inhibitory duplex RNA, but not control small inhibitory duplex RNA, inhibited the mitogen-activated protein kinase signaling cascade and the growth of ARO and FRO cells (P < 0.0001).These effects were mimicked by thyroid carcinoma cell treatment with BAY 43-9006 (IC 50 = 0.5-1 Amol/L; P < 0.0001), whereas the compound had negligible effects in normal thyrocytes. ARO cell tumor xenografts were significantly (P < 0.0001) smaller in nude mice treated with BAY 43-9006 than in control mice. This inhibition was associated with suppression of phospho^mitogen-activated protein kinase levels. Conclusions: BRAF provides signals crucial for proliferation of thyroid carcinoma cells spontaneously harboring the V600E

No abstract

XB130 is a recently cloned 130 kDa-adaptor protein and Src kinase substrate, structurally similar to actin-filamentassociated protein. Here we show that XB130 is predominantly expressed in the thyroid. Given that XB130 is a thyroid-specific tyrosine kinase substrate, we asked whether it is targeted by RET/PTC, a genetically rearranged, constitutively active, thyroid-specific tyrosine kinase that plays a pathogenic role in papillary thyroid cancer. RET/PTC induced robust tyrosine phosphorylation of XB130, which promoted its subsequent association with the p85a subunit of phosphatidylinositol 3-kinase (PI 3-kinase). We identified tyrosine 54 of XB130 as the major target of RET/PTC-mediated phosphorylation and a critical binding site for the SH2 domains of p85a. Importantly, downregulation of XB130 in TPC1 papillary thyroid cancer cells, harboring the RET/PTC1 kinase, strongly reduced Akt activity without altering ERK1/2 phosphorylation, and concomitantly inhibited cell-cycle progression and survival in suspension. In conclusion, XB130 is a novel substrate of the RET/PTC kinase that links RET/PTC signaling to PI 3-kinase activation, and thereby plays an important role in sustaining proliferation and survival of thyroid tumor cells.

To identify genes involved in the transformation of thyroid follicular cells, we explored, using DNA oligonucleotide microarrays, the transcriptional response of PC Cl3 rat thyroid epithelial cells to the ectopic expression of the RET/PTC oncogenes. We found that RET/PTC was able to induce the expression of CXCR4, the receptor for the chemokine CXCL12/SDF-1a/b. We observed that CXCR4 expression correlated with the transforming ability of the oncoprotein and depended on the integrity of the RET/PTC-RAS/ERK signaling pathway. We found that CXCR4 was expressed in RET/PTC-positive human thyroid cancer cell lines, but not in normal thyroid cells. Furthermore, we found CXCR4 expression in human thyroid carcinomas, but not in normal thyroid samples by immunohistochemistry. Since CXCR4 has been recently implicated in tumor proliferation, motility and invasiveness, we asked whether treatment with SDF-1a was able to induce a biological response in thyroid cells. We observed that SDF-1a induced S-phase entry and survival of thyroid cells. Invasion through a reconstituted extracellular matrix was also supported by SDF-1a and inhibited by a blocking antibody to CXCR4. Taken together, these results suggest that human thyroid cancers bearing RET/PTC rearrangements may use the CXCR4/ SDF-1a receptor-ligand pathway to proliferate, survive and migrate.

A r t i c l e A m e n d m e n t sAt the request of the corresponding author, the JCI is retracting this manuscript. The corresponding author recently notified the JCI that multiple microscopy images in Figure 2B were previously published and were used to represent different samples in another publication by the corresponding author's group (1). The authors have stated that experimental data produced ad hoc are consistent with those in the original publication; however, the paper is being retracted due to data duplication and misrepresentation in the original publication. The scatter graph in Figure 4G was incorrect in the print version and the original online version of this article; a correct version of the latter has since been published. The correct figure panel is at right.The JCI regrets the error.

Anaplastic thyroid carcinoma (ATC) is a rare thyroid cancer type with an extremely poor prognosis. Despite appropriate treatment, which includes surgery, radiotherapy, and chemotherapy, this cancer is invariably fatal. CXCR4 is the receptor for the stromal cell-derived factor-1 (SDF-1)/CXCL12 chemokine and it is expressed in a variety of solid tumors, including papillary thyroid carcinoma. Here, we show that ATC cell lines overexpress CXCR4, both at the level of mRNA and protein. Furthermore, we found that CXCR4 was overexpressed in ATC clinical samples, with respect to normal thyroid tissues by real-time PCR and immunohistochemistry. Treatment of ATC cells with SDF-1 induced proliferation and increase in phosphorylation of extracellular signal-regulated kinases and protein kinase B/AKT. These effects were blocked by the specific CXCR4 antagonist AMD3100 and by CXCR4 RNA interference. Moreover, AMD3100 effectively reduced tumor growth in nude mice inoculated with different ATC cells. Thus, we suggest that CXCR4 targeting is a novel potential strategy in the treatment of human ATC. [Cancer Res 2007;67(24):11821-9]

Ponatinib is a potent inhibitor of RET kinase and has promising preclinical activity in models of RET-driven medullary thyroid carcinoma.