P03.24 Downregulation of SMARCB1/INI1 expression in atypical chordomas is associated with upregulation of SMARCB1 regulators miR-671-5p and miR-193a-5p

摘要

>Introduction: Atypical chordomas are relatively rare tumors which arise from the skull base and vertebral column. More frequent in childhood as compared to adults, they are more aggressive with higher incidence of metastasis and a dismal prognosis. Microscopically, they demonstrate atypical or poorly differentiated histology. Recent reports suggest that loss of SMARCB1/INI1/SNF5, a member of the ATP-dependent SWI/SNF chromatin-remodelling complex, is associated with aggressive behavior in a subset of chordomas. However, cause of loss/inactivation of SMARCB1 expression remains elusive, with discrepant results obtained between gene mutation and protein expression. MicroRNAs (miRNAs) are a class of noncoding RNAs that post-transcriptionally down-regulate gene expression through mechanisms of translational repression and mRNA destabilization. They play specific roles in cell proliferation, differentiation and apoptosis. Recent reports suggest that loss of SMARCB1/INI1 expression is regulated by miRNAs viz. miR-206, miR-381, miR-671-5p and miR-193a-5p. We aimed to investigate the expression of these miRNAs in atypical chordomas and correlate the findings with INI1 protein loss. >Methods: In this retrospective study, 12 cases of atypical chordomas diagnosed during a period of 11 years (2006–2016) were retrieved from the archives of the Department of Pathology, AIIMS. Immunohistochemistry for INI1, Fluorescence-in-situ-hybridization for 22q chromosomal region, and mutation analysis for all 9 exons of SMARCB1 were performed. RNA isolation, qRT-PCR for miRNA and mRNA quantification and Pathway analysis using KEGG were performed. >Results: Among the 5 miRNAs analyzed, 4 miRNAs were found to be differentially regulated (downregulated: miR-206; upregulated: miR-381-5p, miR-671-5p and miR-193a-5p) in cases (p<0.05) as compared to control. Notably, miR-671-5p and miR-193a-5p were found to be significantly upregulated in SMARCB1/INI1 immunonegative cases. Pathway analysis for miR-671-5p and miR-193a-5p demonstrated that TGF-β pathway (5 genes SMAD7, ACVR1, ACVR2A, ACVR2B, SP1) was significantly targeted by these miRNAs (p=0.005) and TGF-β1 mRNA levels showed positive correlation with miR-671-5p (R²=0.65, p=0.042) and miR-193a-5p (R²=0.70, p=0.019). Further, expression of TGF-β1 mRNA was significantly upregulated in SMARCB1/INI1 immunonegative cases (p=0.024). >Conclusion: We report for the first time the upregulation of miR-671-5p and miR-193a-5p in SMARCB1/INI1 immunonegative atypical chordomas, with upregulation of TGF-β pathway. TGFβ signaling inhibition is an emerging strategy for cancer therapy and is a potential therapeutic target in atypical chordomas. Additionally, the present study highlights the fundamental role of miRNA mediated epigenetic and post-translational modifications in the pathogenesis and progression of chordomas.