Mitochondria Respiratory Chain Gene Expression Analysis in Renal Cell Carcinoma
Beatriz A Walter Rodriguez, Vladimir A Valera Romero, Marston Linehan, Maria J Merino. NCI/NIN, Bethesda; NCI/NIH, Bethesda
Background: Mitochondrial dysfuction has been proposed as a major pathogenetic mechanism in solid tumors including renal cell carcinomas (RCC). The underlying mechanism is related to both energy production and reactive oxygen species generation by the organelle. The most common morphologic and functional alterations include copy number changes and mt-DNA mutations. However, mRNA expression changes have not been well characterized in RCCs.
Design: A group of 21 renal tumors of different histologies including benign oncocytomas were evaluated.Alterations in the non-coding displacement (D) loop mitochondrial DNA (mt-D Loop) and the 12S mitochondria ribosomal (rRNA)(RNR2) were evaluated by RT-PCR, as well as the expression of the following subunits of the respiratory complex: NADH dehydrogenase 1/2 (complex I), Cytochrome B subunit of the complex III, complex cytochrome c oxidase (COX2) (complex IV) and the mRNA expression of the complex II. HIF-1 A as a surrogate marker of hypoxia activation was assesed in the tumor by IHC.
Results: Analysis of the mt-D Loop mitochondrial content showed that oncocytomas have an increased expression level (7.10 fold-change) in comparison with ccRCC and SDHB mutation-related RCCs (0.18 and 0.58 fold-change). The 12SrRNA expression was also high in Oncocytomas (10.32 fold-change) and decreased in the ccRCC and SDHB-RCC cases (0.56 and 0.85 fold-change), respectively. Complex I subunits evaluated include, ND1 and ND2 genes. ND1 and ND2 expression showed in the oncocytomas high expression level (7.65 and 1.66 fold-change), whereas ccRCC and tumors with SDH mutations showed low expression levels (for ND1 0.24 and 0.22 fold-change and for ND2 0.16 and 0.57 fold-change, respectively). Expression of mRNA of Complex II showed expression level in all the three groups of tumors (oncocytoma, ccRCC and SDHB related tumors). In the SDHB mutated cases, HIF 1 staining shows nuclear positivity only the tumoral cells in the periphery of the tumor mass that is displacing the adjacent normal renal tissue, all the rest of tumor was negative. The clear cell RCC cases, and the oncocytomas showed nuclear accumulation in all tumor cells.
Conclusions: In RCCs, alterations in the expression of mitochondria protein components of respiratory chain are frequent but not in mt copy number. Tumors showed in general low expression level in most the genes. Consistent with the increase in mt content, oncocytomas showed increased expression of most complexes. Hypoxia pathway activation due to HIF1alpha accumulation was not found in RCC with SDH mutation.
Category: Genitourinary (including renal tumors)
Monday, March 19, 2012 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 158, Monday Morning