Che-1 modulates the decision between cell cycle arrest and apoptosis by its binding to p53.

The tumor suppressor p53 is mainly involved in the transcriptional regulation of a large number of growth-arrest- and apoptosis-related genes. However, a clear understanding of which factor/s influences the choice between these two opposing p53-dependent outcomes remains largely elusive. We have previously described that in response to DNA damage, the RNA polymerase II-binding protein Che-1/AATF transcriptionally activates p53. Here, we show that Che-1 binds directly to p53. This interaction essentially occurs in the first hours of DNA damage, whereas it is lost when cells undergo apoptosis in response to posttranscriptional modifications. Moreover, Che-1 sits in a ternary complex with p53 and the oncosuppressor Brca1. Accordingly, our analysis of genome-wide chromatin occupancy by p53 revealed that p53/Che1 interaction results in preferential transactivation of growth arrest p53 target genes over its pro-apoptotic target genes. Notably, exposure of Che-1(+/-) mice to ionizing radiations resulted in enhanced apoptosis of thymocytes, compared with WT mice. These results confirm Che-1 as an important regulator of p53 activity and suggest Che-1 to be a promising yet attractive drug target for cancer therapy.

[p53-regulating pathways as targets for personalized cancer therapy]. / p53-regulierende Signaltransduktionskaskaden als Ziele für eine personalisierte Krebstherapie.

The tumor suppressor p53 acts as a transcription factor downstream of many different stress-induced signaling pathways. Two major groups of p53-controlled genes can be distinguished. Those that mediate the initiation and maintenance of cell cycle checkpoints, and those driving apoptosis. An important determinant of the cellular reaction to DNA damage is the degree of genotoxic stress. The type of cellular response, which ranges from cell cycle arrest to apoptosis depends to a large extend on the severity of the genotoxic lesion. It remains largely unclear which molecular mechanisms govern the cellular decision between p53-driven cell cycle arrest and apoptosis. From a therapeutic perspective, this cellular decision is of utmost importance, as p53-driven apoptosis is therapeutically desired, when treating a malignant disease with DNA-damaging chemotherapy. However, a p53-driven cell cycle arrest might promote chemotherapy resistance, as it allows the tumor cells time to repair genotoxic lesions prior to the next cell division. Here, we summarize recent advances in our understanding of the molecular mechanisms controlling the functional outcome of p53 signaling. We further provide an outlook on the potential development of pharmacological interventions targeting the p53-regulating machinery to promote p53-driven apoptosis, while repressing p53-dependent cell cycle checkpoints.

[Synthetic lethality as a new concept for the treatment of cancer]. / Synthetische Letalität als Therapiekonzept für die Behandlung maligner Neoplasien.

Following DNA damage, cells activate a complex DNA-damage-response (DDR) signaling network to arrest the cell cycle, repair DNA and, if the extend of damage is beyond repair capacity, induce apoptosis. DDR genes are among the most commonly mutated genes in human cancer and it is believed that these lesions promote a "MUTATOR-PHENOTYPE" that fuels the runaway proliferation of cancer cells. However, these genetic lesions can also be seen as the "Achilles heel" of cancer. These tumor cell-specific vulnerabilities are of extraordinary clinical interest, since they allow genetically-guided novel therapeutic regimens for the treatment of cancer. Here, we discuss such a novel therapeutic concept - synthetic lethality. We focus on the first successful clinical applications of synthetic lethality for the treatment of different cancer entities. In addition, we give a brief review of recently developed, synthetic lethality-based approaches that are close to clinical testing.

Atypical Alport syndrome associated with a novel COL4A5 mutation.

Alport syndrome is a progressive hereditary renal disease. Mutations in the genes encoding for three members of the type IV collagen protein family have been found to be the cause of the disease. Alport syndrome is often associated with sensorineural hearing loss and ocular abnormalities, and patients suffering from typical Alport syndrome usually develop end stage renal disease during adolescence or young adulthood. Here we report on a family with atypical Alport disease initially presenting as hereditary focal and segmental glomerulosclerosis. Genetic testing identified a previously undescribed COL4A5 mutation as cause of the disease.

Nephrocystin interacts with Pyk2, p130(Cas), and tensin and triggers phosphorylation of Pyk2.

Juvenile nephronophthisis type 1 is caused by mutations of NPHP1, the gene encoding for nephrocystin. The function of nephrocystin is presently unknown, but the presence of a Src homology 3 domain and its recently described interaction with p130(Cas) suggest that nephrocystin is part of the focal adhesion signaling complex. We generated a nephrocystin-specific antiserum and analyzed the interaction of native nephrocystin with endogenous proteins. Immunoprecipitation of nephrocystin revealed that nephrocystin forms protein complexes with p130(Cas), proline-rich tyrosine kinase 2 (Pyk2), and tensin, indicating that these proteins participate in a common signaling pathway. Expression of nephrocystin resulted in phosphorylation of Pyk2 on tyrosine 402 as well as activation of downstream mitogen-activated protein kinases, such as ERK1 and ERK2. Our findings suggest that nephrocystin helps to recruit Pyk2 to cell matrix adhesions, thereby initiating phosphorylation of Pyk2 and Pyk2-dependent signaling. A lack of functional nephrocystin may compromise Pyk2 signaling in a subset of renal epithelial cells.