Deregulation of the G1/S-phase control in human testicular germ cell tumours

Deregulated cell cycle and defective genome-integrity checkpoints are among the hallmarks of cancer. Here we summarize our recent studies of key components of the G1/S machinery in normal human spermatogenesis, and their abnormalities in testicular germ cell tumours (TGCTs), with special emphasis on carcinoma in situ lesions (CIS). Our combined immunohistochemical and immunoblotting analyses of normal human adult and fetal testes, CIS, seminomas, embryonal carcinomas, and teratomas, revealed an 'unorthodox' spectrum of defects within the so-called RB pathway in TGCTs. The early aberrations included lack of expression of the retinoblastoma tumour suppressor (pRB) and the CDK inhibitor p19ink4d, and overexpression of cyclin D2. Progression from CIS to invasive TGCTs was associated with loss of another two CDK inhibitors and tumour suppressors: p16ink4a and p18ink4c. We also found the lack of pRB and p19ink4d in fetal gonocytes, the candidate target cell for all types of TGCTs. These findings, together with the status of the Chk2-p53 DNA-integrity checkpoint, are considered in relation to the origin, biology and pathogenesis of TGCTs, and potential implications of the G1/S defects for the curability of these tumours.