RET/PTC Oncoproteins: Molecular Targets of New Drugs

The Molecular Basis of Thyroid Epithelial Tumorigenesis

Significant alterations in gene sequences, expression levels and protein structures have been associated with specific types of thyroid epithelial tumorigenesis. Recent revolutionary changes in molecular biology have spanned the disciplines of genomics and proteomics, which systematically generate and analyze the information about genomes, gene transcripts, proteins and their functions in a global, comprehensive manner. The application of these approaches will better discriminate between thyroid tumor subtypes that are not recognizable when traditional pathological criteria are used.

RETMEN2A and RETMEN2B Oncoproteins are Targets of PP1 Inhibitor

Medullary thyroid carcinoma (MTC) responds very poorly to chemotherapy. Mutations in the RET gene are critical for MTC pathogenesis. RET therefore represents a rational target for the development of novel MTC therapies. The accumulation of evidence from laboratory studies strongly suggests that PP1 inhibitor is a cytostatic agent for cells expressing RET oncoproteins. PP1 functions as a potent and selective inhibitor of RET oncoprotein phosphorylation, promoting its proteasomal degradation.

CCDC6: the identity of a protein known to be partner in fusion

Coiled Coil Domain Containing 6 gene, CCDC6, was initially isolated as part of a tumorigenic DNA originated by the fusion of CCDC6 with the tyrosine kinase of RET receptor, following a paracentric inversion of chromosome 10. For a long time, CCDC6 has been considered as an accidental partner of the RET protooncogene, providing the promoter and the first 101 aa necessary for the constitutive activation of the oncogenic Tyrosine Kinase (TK) RET in thyroid cells. With the advent of more refined diagnostic tools and bioinformatic algorithms, an exponential growth in fusion genes discoveries has allowed the identification of CCDC6 as partner of genes other than RET in different tumor types. CCDC6 gene product has a proper role in sustaining the DNA damage checkpoints in response to DNA damage. The inactivation of CCDC6 secondary to chromosomal rearrangements or gene mutations could enhance tumor progression by impairing the apoptotic response upon the DNA damage exposure, contributing to the generation of radio- and chemoresistance. Preclinical studies indicate that the attenuation of CCDC6 in cancer, while conferring a resistance to cisplatinum, sensitizes the cancer cells to the small molecule inhibitors of Poly (ADP-ribose) polymerase (PARP1/2) with a synthetic lethal effect. Several CCDC6 mutations and gene rearrangements have been described so far in different types of cancer and CCDC6 may represent a possible predictive biomarker of tumor resistance to the conventional anticancer treatments. Nevertheless, the detection of a CCDC6 impairment in cancer patients may help to select, in future clinical trials, those patients who could benefit of PARP-inhibitors treatment alone or in combination with other treatments.

Genome-wide studies in thyroid neoplasia

There is much interest in the application of genome biology to the field of thyroid neoplasia, despite the relatively low mortality rate associated with thyroid cancer in general. The principal reason for this interest is that the field of thyroid neoplasia stands to benefit from the application of genomic information to address a variety of pathologic and clinical issues. In addition to practical patient care issues, there is an excellent opportunity of expand the basic understanding of thyroid carcinogenesis. In this article, the most relevant genomic work on thyroid tumors performed to date is reviewed along with some general comments about the potential impact of genomic biology on thyroid pathology and the management of patients with thyroid nodules and cancer.