Spontaneous and radiation-induced leukemogenesis of the mouse small eye mutant, Pax6(Sey3H)

Tumor suppressor PAX6 functions as androgen receptor co-repressor to inhibit prostate cancer growth

BACKGROUND

PAX6, a transcription factor, has currently been suggested to function as a tumor suppressor in glioblastoma and to act as an early differentiation marker for neuroendocrine cells. The androgen receptor (AR) plays a pivotal role in prostate cancer development and progression due to its transcriptional activity in regulating genes involved in cell growth, differentiation, and apoptosis. To determine the role of PAX6 in prostate cancer, we investigated whether PAX6 interacts with AR to affect prostate cancer development.

METHODS

We used immunostaining, RT-PCR, and Western blotting assays to show the expression status of PAX6 in prostate tissue and human prostate cancer cell lines. The role of PAX6 in cell growth and colony regeneration potential of LNCaP cells were evaluated by MTT assay and soft agar assay with PAX6-overexpressed LNCaP cells. Mammalian two-hybrid and co-immunoprecipitation (Co-IP) assays were used to demonstrate the interaction between PAX6 and AR. Reporter gene and Q-RT-PCR assays were performed to determine the effects of PAX6 on the function of AR.

RESULTS

In prostate cancer tissues, PAX6 expression was stronger in normal epithelial cells than cancer cells, and decreased in LNCaP cells compared to that of DU145 and PC3 cells. Enforced expression of PAX6 suppressed the cell growth of LNCaP cells and also inhibited the colony formation of LNCaP cells. PAX 6 interacted with AR and repressed its transcriptional activity. PAX6 overexpression decreased the expression of androgen target gene PSA in LNCaP cells.

CONCLUSIONS

In this study, we found that PAX6 may act as a prostate cancer repressor by interacting with AR and repressing the transcriptional activity and target gene expression of AR to regulate cell growth and regeneration.

Intestinal tumorigenicity of mice carrying hemizygous Pax6, Pax6(Sey-4H)

The genotype-phenotype relationship in mice was examined experimentally using one of the small eye mutants, Pax6(Sey-4H), which deletes the chromosome 2 middle region, hemizygously. The genotyping indicated that the deleted region starts at a site 102.60 Mb from the centromere and has a length of 6.51 Mb, in which 12 known and 27 novel genes are located. Expecting the development of myeloid leukemia, gamma-irradiation was performed to female mutants at the age of 10 weeks. The mutants did not develop myeloid leukemia during the observation period of 18 months. Instead, they developed tumors in the alimentary tract spontaneously (56.0%). The tumor latency was shortened by the radiation exposure, but the tumor incidence of the gamma-irradiated group (62.5%) was as high as that of spontaneously developing tumors. Intraductal proliferation of the epithelium of the Wirsung duct was observed in the gamma-irradiated mutants (18.8%). Considering the results of the Pax6(Sey-4H) mutant together with those of another small eye mutant, Pax6(Sey-3H), the anomaly and the tumorigenicity of the intestinal tract were closely related to the hemizygosity of the 3.2 Mb segment of chromosome 2, where both mutants show a common deletion.

Comparison of the effectiveness of high and low LET radiations for the proportion of survivals with liver tumors at every age in (C57BL/6N x C3H/HeN) F1 mice

To investigate the late effects of neutrons at the energy below 1 MeV on the liver carcinogenesis as a function of age, one-week old mice were exposed to 1.0 Gy monoenergetic neutrons (0.317, 0.525 and 1.026 MeV) or 137Cs gamma rays. Survival and carcinogenesis were examined by 18 months of age. Following radiation, tumor incidences in liver, Harderian gland, lung, ovary and pituitary gland were compared. The proportion of the lifespan with liver tumors exposed to neutrons to that exposed to gamma rays was calculated as a function of age. Survival rates among the three groups exposed to neutrons of different energies were not significantly different from one another but shorter than those treated with gamma rays for both sexes. With regard to liver tumor incidence evaluated at 18 months of age, the effectiveness of neutrons to gamma rays was 2.54 for females, and 2.08 for males by the factor. Levels of estrogen in the serum were similar between mice bearing liver tumors and those devoid of tumors. In conclusion, all three energies of neutrons induced similar effectiveness with respect to liver carcinogenicity. Proportions of the lifespan with liver tumors of neutron-exposed to gamma-exposed were shorter in females than males along with ages over 12 months. To obtain this factor at every age contributed for the evaluation of the biological effectiveness of radiations with the parameter of tumor incidence and latency simultaneously.