Medullary thyroid cancer (MTC) represents only 3-5% of thyroid cancers. The dominant oncogene mutated in MTC is proto-oncogene RET. The analysis of the genotype¿phenotype correlation clearly indicates that not all mutations of RET have same effect on MTC clinical features, and consequently patients shown different response to treatment.
A mutation in RET gene lead to constitutive activation and aberrant expression or activation of receptor, but also it can be involved in a specific molecular mechanisms that modulate RET expression. Most of the mechanisms by which RET expression is modulate are unknown.
In recent years have been studied a broad spectrum of molecular events involved in oncogene regulation that can drive tumorigenesis.
The aim of this project is to improve the knowledge of molecular mechanisms involved in regulation of RET proto-oncogene expression at genetic, expression and protein level.
For this aim, we would like to study the molecular mechanism of a new germ-line synonymous substitution on on RET proto-oncogene expression.
The germ-line synonymous substitution was harbored by a patient with a very aggressive form of MTC; synonymous substitution was found in-cis with another somatic gain-of-function RET mutation. We collected several data suggesting the implication of a new oncogenic mechanism by which synonymous mutations could strengthen activation of mutated oncogene. To demonstrate the mechanism by which synonymous substitution affects RET expression, we decide to performed several in vitro experiments using RET minigenes.
In recent years the new interest on synonymous mutations and the discovery of their involvement in expression gene regulation have lead to reanalyzed the data of next generation sequence obtain in different cancer studies and give a new meaning of ¿silent mutation¿ 10. Supek et al. found in a huge cohort of human cancers the presence of synonymous mutations, from 20 to 50% were found in oncogenes and most of them were included in 30 nucleotides of exons boundary. Using predictive software, the authors found that these synonymous mutations lead to gain of ESE motifs or loss of ESS motifs 10. Nowadays all splicing mutations reported affect the quality of a transcript with the resulted exon skipping, intron retention, deletion or insertion of portion of exons, presence of cryptic exon 11.
We collected several data suggesting the implication of a new oncogenic mechanism by which synonymous mutations could strengthen activation of a mutated oncogene. Synonymous mutation found in RET gene affects the quantity of the transcript lead to overexpression of oncogene. This mechanism is never described in literature.
Starting the study from a very aggressive case of medullary thyroid cancer, our aim is demonstrate this new mechanism by which the synonymous mutation affects the aggressiveness and lead to the worsening of the disease in this patient.
This mechanism is another evidence of the influence of synonymous mutations on tumor phenotype. In particular, the overexpression of RET due to ESE introduced by C630C can be included in the group of mechanisms that modulate the aggressiveness in cancer. Supek et al. demonstrate through predictive software that synonymous mutations in boundary of exons in oncogenes maybe lead to ESE gain. We would demonstrate that ESE motifs gain in an oncogene affects the gene expression also if don¿t affects the splicing of a transcript. This mechanism maybe involved others kind of cancer, and synonymous substitutions in regulative region of a gene can involve other oncogenes.
10. Supek F, Miñana B, Valcárcel J, Gabaldón T, Lehner B. Cell. 2014;156(6):1324-1335. doi:10.1016/j.cell.2014.01.051.
11. Diederichs S, Bartsch L, Berkmann JC, et al. EMBO Mol Med. 2016;8(5):1-16. doi:10.15252/emmm.201506055.