AIMTo analyze the functional interactions of Cyclin with p53 and Atm in spermatogenesis and DNA double-strand break repair.

METHODSTwo lines of double knockout mice were generated. Spermatogenesis and double strand break repair mechanisms were analyzed in Cyclin A1 (Ccna1); p53- and Ccna1; Atm-double knockout mice.

RESULTSThe block in spermatogenesis observed in Cyclin A1-/- (Ccna1-/-) testes at the mid-diplotene stage is associated with polynucleated giant cells. We found that Ccna1-deficient testes and especially the giant cells accumulate unrepaired DNA double-strand breaks, as detected by immunohistochemistry for phosphorylated H2AX. In addition, the giant cells escape from apoptosis. The development of giant cells occurred in meiotic prophase I, because testes lacking ATM, which are known to develop spermatogenic arrest earlier than prophase I, do not develop giant cells in the absence of cyclin A1. Cyclin A1 interacted with p53 and phosphorylated p53 in complex with CDK2. Interestingly, p53-deficiency significantly increased the number of giant cells in Ccna1-deficient testes. Gene expression analyses of a panel of DNA repair genes in the mutant testes revealed that none of the genes examined were consistently misregulated in the absence of cyclin A1.

CONCLUSIONCcna1-deficiency in spermatogenesis is associated with defects in DNA double-strand break repair, which is enhanced by loss of p53.

Animals ; Ataxia Telangiectasia Mutated Proteins ; Cell Cycle ; genetics ; physiology ; Cell Cycle Proteins ; genetics ; metabolism ; Cyclin A ; genetics ; metabolism ; Cyclin A1 ; Cyclin B ; Cyclin B2 ; DNA ; genetics ; DNA Repair ; genetics ; physiology ; DNA-Binding Proteins ; genetics ; metabolism ; Gene Expression Regulation ; genetics ; physiology ; Male ; Mice ; Mice, Knockout ; Protein-Serine-Threonine Kinases ; genetics ; metabolism ; Spermatogenesis ; genetics ; physiology ; Testis ; cytology ; metabolism ; Tumor Suppressor Protein p53 ; genetics ; metabolism ; Tumor Suppressor Proteins ; genetics ; metabolism

Progressive multifocal leukoencephalopathy (PML) is a devastating neurological disease observed nearly exclusively in immunocompromised patients. Recently, the introduction of monoclonal antibodies significantly inhibiting the immune system such as rituximab has led to an increase in PML cases. Although rituximab-based immunochemotherapy remains the standard of treatment for chronic lymphocytic leukemia (CLL), the importance of Bruton’s tyrosine kinase inhibitors such as ibrutinib is steadily increasing. However, long-term experiences regarding possible side effects of these new substances are rare. Here, we report the development of eventually fatal PML possibly associated with ibrutinib therapy for CLL after multiple prior treatment lines, including rituximab. To the best of our knowledge, this is the first study to report such findings. Since the last course of rituximab was applied over 3 years ago, it is conceivable that the strong B cell inhibition by ibrutinib led to PML. With increased awareness of this potential side effect, further clinical studies are certainly warranted to evaluate this possible association.
Antibodies, Monoclonal ; Immune System ; Immunocompromised Host ; JC Virus ; Leukemia, Lymphocytic, Chronic, B-Cell* ; Leukoencephalopathy, Progressive Multifocal* ; Protein-Tyrosine Kinases ; Rituximab