Purpose: Down-regulation of the IAP antagonistis XAF1, Smac/DIABLO and HtrA2, has been related to the onset and progression of various malignancies. We examined the mRNA-expression of these pro-apoptotic parameters in testicular germ cell tumors (TGCT) and normal testicular tissue and correlated their expression levels to clinicopathological tumour features.
Material and methods: Real-time RT-PCR was used to quantify the mRNA-expression of XAF1, Smac/DIABLO and HtrA2 in normal testicular tissue (n = 18), carcinoma in situ (n = 4), seminomas (n = 64), and non-seminomatous germ cell tumors (n = 35).
Results: Compared to normal testicular tissue, the expression levels of XAF1 were increased in TGCT (p < 0.001), whereas those of Smac/DIABLO and HtrA2 were decreased (p < 0.001 and p < 0.001). Smac/DIABLO expression levels showed a significant trend towards a gradual decrease from normal testicular tissue to CIS and seminomas and finally to NSGCT (p < 0.001). Moreover, XAF1 and HtrA2 expression levels gradually increased with progression of clinical tumour stage in seminoma patients (p = 0.001 and p = 0.018), their expression levels being strongly intercorrelated (Spearman rho correlation coefficient: 0.674; p < 0.001).
Conclusion: These data suggest that a down-regulation of Smac/DIABLO and HtrA2 is implicated in the development and progression of TGCT, whereas overexpression of XAF1 in TGCT might contribute to their extraordinary sensitivity to chemotherapy. Regarding the additional correlation of XAF1 and HtrA2 expression with clinical tumour stage in seminoma patients, it appears reasonable to further evaluate these three IAP antagonists as molecular parameters for the prediction of treatment response and prognosis of TGCT patients.