Dynamics of caspase activation upon UV induced genotoxic injury.

PURPOSE: Caspases are common mediators of cell death. Evasion of cell death including apoptosis are considered to be hallmarks of cancer. A deeper understanding of the apoptotic cascade may aid improving cancer therapies. Our aim was to characterize the progression of cell death following UV-induced genotoxic injury in a defined cell culture model. MATERIALS AND METHODS: Hela cells were UV-irradiated with doses ranging from 0.1 to 60 mJ/cm2. Cells were counted and colony forming assays were performed with caspase inhibitors. RESULTS: In our model of HeLa cells, cells remain >90% viable until 6 hrs after UV radiation (UVR), but more than half of the cells are dead after 12 - 72 hrs after UVR. Within a dose range between 0.1 and 50 mJ/cm2, viability ranges roughly between 20 and 30%. The difference between the lowest dose applied (0.1 mJ/cm2) and the other doses applied is significant, with the exception of the next higher dose of 1 mJ/cm2. The activation of caspases precedes the cell death induction by several hrs. Caspase-9 starts to be activated at 1 hr after UVR followed by caspases 3, 6 and 7 which are fully active at 2 hrs after UVR while caspase-8 is fully active only 3 hrs after UVR. Most caspases are only weakly or not active at 0.1 mJ/cm2 after 3 hrs, but fully active at the same time point with increased radiation doses. PARP-1, a caspase substrate, is cleaved immediately after activation of the caspases. Colony formation activity of the tumor cells decreases exponentially after UVR dropping down to < 0.01% plating efficiency at a dose of 60 mJ/cm2. Interestingly, this drop in plating efficiency cannot be rescued by any of the two caspase inhibitors tested. CONCLUSIONS: UV-induced cell death in this model involves the activation of apoptosis-related caspases, but this activation seems to be dispensable for the execution of cell death. Further experiments should clarify which mechanisms of cell death are really necessary for the execution of this type of cell death.

GT-repeat extension in the IL11 promoter is associated with Hirschsprung's disease (HSCR).

Hirschsprung's disease (HSCR) is a congenital disease characterized by intestinal obstruction due to a defective intestinal neural system. Frequently, the disease is associated with an intestinal inflammation. The most common known underlying genetic alterations are in the RET gene but HSCR can also be caused by mutations in other genes that are responsible for the maturation and migration of intestinal neural cells. Recently, a study in an Asian population reported a significant association of several single nucleotide polymorphisms (SNPs) in the IL11 (interleukin 11) gene with HSCR. We further explored the possible association of genetic alterations in the IL11 gene with HSCR and HSCR subtypes in an unrelated Caucasian population. We used a targeted sequencing approach to identify a total of 32 SNPs covering the coding region of the IL11 gene including the proximal part of the promoter and relevant SNPs described in the previous study. Genotype frequencies were compared using additive genetic models in 103 HSCR patients and 128 healthy controls. We failed to observe any significant association of SNPs with HSCR. However, there was a suggestive evidence for an association of the length of a dinucleotide repeat in the IL11 promoter region with HSCR with an over-representation of >7 GT repeat subtypes (OR = 4.982 (1.448-17.040), p-value = 0.0111) in HSCR patients. A similar trend was further observed in a subgroup of patients with long-segment HSCR (L-HSCR). These findings need to be replicated in a well-powered study. Changes in IL11 expression may be a link to the intestinal inflammation frequently observed in patients with HSCR.

Genetic mosaicism of a frameshift mutation in the RET gene in a family with Hirschsprung disease.

Mutations and polymorphisms in the RET gene are a major cause of Hirschsprung disease (HSCR). Theoretically, all true heterozygous patients with a new manifestation of a genetically determined disease must have parents with a genetic mosaicism of some extent. However, no genetic mosaicism has been described for the RET gene in HSCR yet. Therefore, we analyzed families with mutations in the RET gene for genetic mosaicism in the parents of the patients. Blood samples were taken from patients with HSCR and their families/parents to sequence the RET coding region. Among 125 families with HSCR, 33 families with RET mutations were analyzed. In one family, we detected a frameshift mutation due to a loss of one in a row of four cytosines in codon 117/118 of the RET gene (c.352delC) leading to a frameshift mutation in the protein (p.Leu118Cysfs*105) that affected two siblings. In the blood sample of the asymptomatic father we found a genetic mosaicism of this mutation which was confirmed in two independent samples of saliva and hair roots. Quantification of peak-heights and comparison with different mixtures of normal and mutated plasmid DNA suggested that the mutation occurred in the early morula stadium of the founder, between the 4- and 8-cell stages. We conclude that the presence of a RET mutation leading to loss of one functional allele in 20 to 25% of the cells is not sufficient to cause HSCR. The possibility of a mosaicism has to be kept in mind during genetic counseling for inherited diseases.