DICER1 and TARBP2 gene analysis in adult and pediatric adrenocortical tumors

Author(s)

Gabriela Resende Vieira de Sousa

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina (FM/SBD)
• Defense date: 2015-07-31

Examining board members

Madson Queiroz de Almeida; Sonir Roberto Rauber Antonini; Tânia Aparecida Sartori Sanchez Bachega

• Advisor: Madson Queiroz de Almeida

Abstract

INTRODUCTION: Adrenocortical cancer is a rare neoplasia with an estimated incidence of 0.5-2.0/million/year in adults. There are currently few therapeutic options for patients with adrenocortical cancer, and new insights into the pathogenesis of this lethal disease are needed. The microRNA (miRNA) expression profile of human tumors has been characterized by an overall miRNA downregulation. DICER1 enzyme and its cofactor TRBP are a key component of the miRNA processing machinery. It was recently demonstrated that escaping miRNA control in cancer cells due to Dicer downregulation may allow the phenotypic emergence of more aggressive genetic variants, accelerating cancer progression. Recently, DICER1 mutations in the RNase IIIb domain were found in 29% of nonepithelial ovarian tumors, predominantly in Sertoli-Leydig cell tumors (60%). In addition, TARBP2 truncating mutations, causing DICER1 destabilization, were identified in tumor cell lines with microsatellite instability. AIM: To study the mRNA and protein expression of DICER1 and TRBP in adult and pediatric adrenocortical tumors; To investigate DICER1 mutations in metal biding sites located at the RNase IIIb domain; To investigate inactivating mutations in the exon 5 of TARBP2 gene; To determine the expression of miR-103 and miR-107, DICER1 regulators, and miR-497, a TRBP regulator. METHODS: Protein expression of DICER1 and TRBP was evaluated by immunohistochemistry in a tissue microarray with 198 adrenocortical tumors [154 in adults (75 adenomas and 79 carcinomas) and 44 in children (38 clinically benign and 6 malignant)]. Expression of DICER1 and TARBP2 genes was assessed in a subgroup of 84 tumors (61 adults and 23 children) and miRNA expression in 82 tumors (59 adults and 23 children). The DICER1 and TARBP2 gene sequencing was performed in a subgroup of 83 tumors. RESULTS: In adults, a strong DICER1 expression was demonstrated in 39 out of 79 carcinomas (51%) and in 24 out of 75 adenomas (32% X2= 4.8, p= 0.028). Similarly, DICER1 gene overexpression was demonstrated in 15 out of 25 carcinomas (60%) and in 7 out of 30 adenomas (23%; X2= 7.64, p= 0.006). Among adult adrenocortical carcinomas, a weak DICER1 expression was significantly more frequent in metastatic than in non-metastatic adrenocortical carcinomas (66% vs. 31%; X2= 9.3, p= 0.002). Besides being more aggressive, adult adrenocortical carcinomas with a weak DICER expression were diagnosed in younger patients (median 35 vs. 45 yrs, p= 0.02) and had larger size (12.3 vs. 9 cm, p= 0.001), more advanced staging (ENSAT 3 or 4 in 55% vs. 30%, p= 0.04) and higher Weiss score (6 vs. 4, p= 0.02). Additionally, a weak DICER1 expression was significantly correlated with a reduced overall (p= 0.004) and disease-free (p= 0.005) survival. In the multivariate analysis, Ki67 >- 10% (p= 0.0001) and a weak DICER1 expression (p= 0.048) remained as independent predictors of recurrence. In the pediatric group, DICER protein and gene expression was not different between clinically benign and malignant tumors. No variant was identified in the metal binding sites of the RNase IIIb domain of DICER1 gene in both adult and pediatric tumors. Furthermore, DICER1 protein and gene expression did not correlate with miR-103 e miR-107 expression. miR-107 was overexpressed in adult carcinomas compared to adenomas, but it was not a predictor of poor outcome. Regarding TARBP2 gene, its gene and protein expression did not correlate with histopathological and clinical parameters in both children and adults. No variant was identified in exon 5 TARBP2 gene. Additionally, miR-497 was not expressed neither in the normal adrenal cortex and in adrenocortical tumors. CONCLUSION: A weak DICER1 protein expression was significantly associated with poor outcome in adult adrenocortical carcinomas. However, DICER1 deregulation in adult ACCs was not caused by mutations within the RNase IIIb domain and not associated with expression of its regulatory miRNAs. Although miR-107 was overexpressed in adult adrenocortical carcinomas, its expression was not correlated with a reduced survival. Finally, TARBP2 gene and protein expression was not associated with poor outcome in adrenocortical tumors (AU)

• FAPESP's process: 13/09621-8 - Analysis of DICER1 gene in pediatric and adult adrenocortical tumors
• Grantee: Gabriela Resende Vieira de Sousa
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)