Ekspresija i varijante gena za tumorski supresor VHL u papilarnim karcinomima štitaste žlezde

Abstract

Papilarni karcinomi štitaste žlezde (PTC) predstavljaju najučestalije karcinome endokrinog porekla. Poslednjih decenija, incidenca ovih karcinoma je u stalnom porastu zbog čega je identifikacija molekularnih markera koji bi doprineli preciznijoj klasifikaciji bolesnika sa rizikom za progresiju bolesti, a u cilju izbora terapijskog pristupa, od izuzetnog kliničkog značaja. Gen VHL uključen je u tumorigenezu različitih tipova karcinoma i u mnogima od njih je povezan sa agresivnijim biološkim ponašanjem. Uloga i značaj VHL u patogenezi i progresiji PTC do sada nisu ispitivani. Predmet ove studije bio je ispitivanje nivoa ekspresije VHL u PTC. Ekspresioni profili VHL iRNK i proteina određeni su metodama PCR u realnom vremenu i imunohistohemijom. Istovremeno, ispitano je da li su mutacioni događaji u kodirajućoj sekvenci gena i regulacija koja se odvija na post-transkripcionom nivou a posredovana je miR-92a, odgovorni za detektovane različite nivoe ekspresije VHL. Sekvenciranjem sva tri egzona gena VHL nisu detektovane mutacione promene. Nivo ekspresije miR- 92a, iako izmenjen, nije značajno korelisao sa nivoima ekspresije VHL iRNK i proteina. Ovi rezultati ukazuju na to da su za promene u ekspresiji VHL verovatno odgovorni neki drugi regulatorni mehanizmi. U odnosu na nivo ekspresije VHL iRNK u PTC i odgovarajućem neizmenjenom tireoidnom tkivu, utvrđeno je da postoje dve grupe bolesnika – oni sa sniženom i oni sa povišenom ekspresijom VHL u tumorskom tkivu. Detektovane promene ekspresionog profila VHL u korelaciji su sa kliničkim i patohistološkim parametrima PTC. Takođe, utvrđeno je da je niska ekspresija VHL iRNK povezana sa kliničkim i patohistološkim karakteristikama koje ukazuju na agresivnije ponašanje tumora, kao i da je povezana sa kraćim trajanjem vremenskog perioda bez znakova bolesti. Rezultati ove studije sugerišu da bi evaluacija ekspresije VHL tumorskog supresora mogla imati klinički značaj u prognozi agresivnijeg toka bolesti kod bolesnika sa PTC.

Papillary thyroid carcinomas (PTC) represent the most prevalent type of endocrine malignancy. Over the last decades their incidence has been increasing, underlining the significance of the identification of molecular markers which would improve the risk stratification and help optimize the therapeutic approach to PTC patients. While the VHL gene is implicated in tumorigenesis of different types of carcinoma and has been reported to be associated with more aggressive biological behavior, its importance in the patogenesis and progression of PTC has not been explored so far. The subject of this study was to investigate the expression level of VHL in this type of carcinoma. The expression profiles of VHL mRNA and protein were determined using real time PCR and immunohistochemistry. In addition, it was investigated whether mutations in the coding sequence and post-transcriptional expression regulation mediated with miR-92a were responsible for VHL expression alterations detected in this study. No mutations were detected by sequencing of all three exons of the VHL gene. The expression level of miR-92a, although altered, did not show significant correlation with VHL mRNA and protein levels. These results suggest that probably some other regulatory mechanisms are responsible for VHL expression alterations. The analysis of VHL mRNA expression levels in PTC tissues compared to matched non-tumour tissues revealed that there were two groups of patients – patients with a decreased VHL expression level and patients with an increased expression level in tumour tissue. The detected VHL expression profile alterations were in correlation with PTC clinicopathological parameters. Moreover, low VHL expression was associated with more aggressive tumour features and with a shorter disease free interval. The results of this study suggest that evaluation of VHL tumor suppressor expression level might have significance in the prognosis of more aggressive course of the disease in PTC patients.