Role of LIN28, an RNA-binding protein, in adrenocortical tumorigenesis

Author(s)

André Murad Faria

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina (FM/SBD)
• Defense date: 2014-12-08

Examining board members

Madson Queiroz de Almeida; Venancio Avancini Ferreira Alves; Sonir Roberto Rauber Antonini; Tânia Aparecida Sartori Sanchez Bachega; Cláudio Elias Kater

• Advisor: Madson Queiroz de Almeida

Abstract

INTRODUCTION: Adrenocortical carcinoma is a rare neoplasm with overall poor prognosis. Recently, several studies demonstrated the potential of miRNA profiling in differentiating between adrenocortical adenomas and carcinomas, risk stratification and prognosis. Nevertheless, little is known about posttranscriptional regulation of miRNAs. LIN28 is a highly conserved RNA-binding protein that has emerged as a modulator of the processing of let-7, an important family of miRNAs widely known for its tumor-suppressive effects. Besides from let-7, LIN28 has also shown to regulate and be regulated by mir-9, mir-30 and mir-125. OBJECTIVES: To analyze LIN28 gene and protein expression in a large cohort of adult and pediatric adrenocotical tumors (ACTs), and investigate the copy number variation analysis for LIN28A and LIN28B genes and the expression of LIN28 regulatory microRNAs (let-7 family, mir-9, mir-30 e mir-125) in a subgroup of this cohort. METHODS: LIN28 protein expression was assessed in a total of 266 adult (78 adenomas and 188 carcinomas) and 44 pediatric ACTs (35 clinically benign and 9 clinically malignant). LIN28A and LIN28B gene expression was evaluated in a subgroup of 86 adult and pediatric ACTs and copy number variation analysis of these genes in 58 ACTs. The expression of let-7 family, mir-9, mir-30 and mir-125 was performed in 28 adult carcinomas. RESULTS: In adults, LIN28A gene was overexpressed in aggressive carcinomas when compared with adenomas [7.0 fold change (from 0 to 174.3) vs. 3.6 (from 0 to 18.3); p = 0.006, respectively] and a trend towards greaten expression when compared with non-aggressive carcinomas [7.0 (from 0 to 174.3) vs. 7.1 (from 0 to 17.1); p = 0.092]. LIN28B expression was undetectable in the great majority (92%) of adult ACTs. Surprisingly, weak LIN28 staining was significantly associated with reduced disease-free survival in this population (p = 0.01), but for overall survival only a trend was detectable (p= 0.117). In the multivariate analysis, only Ki67 index >- 10% (HR 5.7, 95% CI 3.0-10.8; p = 0,0001) and weak LIN28 staining (HR 2.3, 95% CI 1.2-4.4; p = 0,008) were independent predictors of recurrence in adult patients. Interestingly, mir-9 expression, a negative LIN28A/B regulator, was significantly higher in aggressive than in non-aggressive ACCs [2076 (from 36 to 9307) vs. 133.4 (from 2.4 to 5193); p = 0.011] and was highly associated with reduced overall survival ( p= 0.01) and disease-free survival (p = 0.01). In the pediatric population, no significant difference was observed in the expression of LIN28 protein and LIN28A and mir-9 gene expression between clinically benign and clinically malignant tumors. Additionally. overexpression of LIN28B was significantly associated with reduced disease-free survival (p = 0.026), but not with overall survival (p = 0.406). Copy number variation analysis showed that only a child with a virilizing benign tumor had LIN28B amplification and a woman with a metastatic adrenocortical carcinoma had LIN28B deletion. No LIN28A copy number variation was detected. A Ki67 >= 20% in children was able to discriminate patient with worse prognosis: there was a significant associtation with reduced overall (p = 0,015) and disease-free survival (p = 0,001) in 36 pediatric ACTs with Weiss >- 3. CONCLUSIONS: Weak LIN28 staining was associated with reduced disease-free survival in a large cohort of adult adrenocortical carcinoma. LIN28A had higher expression in aggressive carcinomas in adults, suggesting there might be negative posttranscriptional regulation of LIN28 protein expression. Interestingly, overexpression of mir-9, a negative LIN28A regulator, predicted poor outcome in adult patients. In addition, LIN28B overexpression was an potential marker of poor prognosis in the pediatric population. A Ki67 index >- 10% in adults and >- 20% in children were associated with poor prognosis (AU)

• FAPESP's process: 11/09092-0 - Role of LIN28, a RNA-binding protein, in adrenocortical tumorigenesis
• Grantee: André Murad Faria
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)