Aberrations of DNA-copy number and expression of PARK2 and PACRG in cc-RCC: correlation with clinico-pathological parameters and prognosis
M.I.Toma1*, D. Wuttig²*, S. Kaiser², S. Füssel², T. Weber², M.O.Grimm², M.P. Wirth², G.B. Baretton1
1 Institut für Pathologie, Universitätsklinikum Carl Gustav Carus, Dresden
2 Klinik und Poliklinik für Urologie, Universitätsklinikum Carl Gustav Carus, Dresden
*Both authors contributed equally to this study
Aims: The present study correlates PARK2 and PACRG expression with copy number abnormalities, clinico-pathological parameters and survival in cc-RCC.
Methods: RNA and DNA were isolated from fresh-frozen primary ccRCC samples and corresponding non-malignant tissues from 100 patients (59 male, 41 female, median age 63 years). Follow-up data were available for 80 patients. mRNA expression and copy number analyses were performed by quantitative PCR on the LightCycler 480 (Roche) using gene-specific TaqMan gene expression and copy number assays Relative quantification was performed by the deltadeltaCT method using non-malignant tissue (mRNA expression) or lymphocyte DNA of healthy donors (copy number; n=20) as reference. Statistical analysis was done by SPSS 17 for Windows.
Results: Eighty patients had an organ-confined, 20 a non-organ-confined tumor. Five patients showed a G1, 76 a G2 and 19 a G3 tumor. PACRG was significantly down-regulated in ccRCC compared to corresponding normal kidney tissue (p < 0.001). A lower expression was found in 92 tumours, whereby 66 cases showed a complete loss of PACRG expression. PACRG expression was reduced in higher tumor stages (I/II vs. III/IV, p=0.046), and in metastasized tumors (p = 0.012). A complete loss of PACRG expression was associated with a significantly shorter disease-free survival (p=0.046). A down-regulation of PARK2 was demonstrated in 57% of cc-RCC (p<0.001), in 13 cases with a complete loss of PARK2 expression. A reduced PARK2 expression was associated with higher tumor stage (p=0.034), grade (p =0.004) and metastatic spread (p=0.02). DNA copy number analysis showed losses of PACRG in 47% of cases, but the down-regulation of PACRG is not always associated with low PACRG DNA copy number.
Conclusions: Loss of PACRG and PARK2 are common events in cc-RCC and are associated with aggressive disease. PACRG and PARK2 might represent tumor suppressors in ccRCC and their loss is involved in tumor progression as it has been reported for a few other tumor entities.