JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

3-43
Nuclear Localization of a FOXO Transcriptional
Factor DAF-16 in C. elegans, which is Required in
a Response to IR Irradiation
T. Kimura a) , T. Takanami a) , T. Sakashita b) , Y. Kobayashi b) and A. Higashitani a)
a) Graduate School of Life Sciences, Tohoku University,
b) Radiation-Applied Biology Division, QuBS, JAEA
We have identified that certain genes including F49F1.6
induced by ionizing radiation (IR). Also, their induction
has been observed during infection of Psudomonas
aeruginosa as innate immune response 1) . F49F1.6 gene
product has a signal peptide and Metridin-like ShK toxin
domain and shows good similarity to the N-terminal region
of mammalian Mucin-2 precursor 2) . We have also found
consensus sequences for GATA-1 and DAF-16
transcriptional factors in the transcriptional promoter region.
By using RNAi technology, ELT-2 (a GATA-type
transcription factor) is required specifically for responses to
IR and bacterial infection. In this study, we analyzed the
function of another transcription factor DAF-16 in response
to IR.
DAF-16 codes the Forkhead box O (FoxO) transcription
factor family that acts in an insulin-mediated pathway to
affect dauer formation, and that also affects life span, innate
1, 3)
immunity and reproduction . It is orthologous to human
FOXO1, -3, -4 and -6. In the daf-16 mutant, induction levels
of F49F1.6 gene following IR irradiation were decreased as
compared with those of wild type (Fig. 1). Oppositely,
those of the daf-2 mutant were increased (Fig. 1). It has
been reported that DAF-2 signals negatively regulate the
3)
activity of DAF-16 . These results indicate that DAF-16
functions as a transcriptional factor to induce certain genes
including F49F1.6 in response to IR irradiation.
The daf-16 gene is broadly expressed in most cells
except for the cells in the pharynx and in the somatic
2, 4)
gonad . In addition, its nuclear transport in response to
environmental stress such as high temperatures is
4)
described . We therefore investigated whether DAF-16
translocates from cytoplasm to nuclei following IR
irradiation by using a recombinant strain expressed a
DAF-16::GFP fusion protein. The results shown in
Fig. 2A indicated that strong signals of DAF-16::GFP were
revealed in cytoplasm of gut and body wall cells of control
animals. Following IR irradiation, the signals were
translocated into nuclei of these cells as well as those of
high temperatures treatments (Fig. 2B, C). It clearly
indicates that IR caused nuclear localization of DAF-16
protein, and it might act as a transcription factor for certain
genes including F49F1.6 in response to IR.
We are now attempting to study whether the nuclear
localization caused by IR is driven through either oxidative
stress or DNA damage response. Moreover, in addition to
ELT-2 (GATA) and DAF-16 (FoxO), PMK-1 (p38 MAPK)
is required for F49F1.6 induction by IR irradiation. The
JAEA-Review 2010-065
- 99 -
next challenge is to resolve the complex regulatory
mechanism with these factors.
References
1) E.R. Troemel et al., PLoS Genet. 2 (2006) e183.
2) WormBase., http://www.wormbase.org/.
3) C.L. Kurz &M-W. Tan, Aging Cell 3 (2004) 185.
4) S.T. Henderson & T.E. Johnson, Curr. Biol. 11 (2001)
1975.
Fig. 1 A FoxO factor DAF-16 is required for F49F1.6
gene expression induced by 100 Gy X-ray irradiation.
Fig. 2 Nuclear localization of DAF-16 following IR
irradiation. A: control of DAF-16::GFP in TJ356
strain, B: high temperature treatment at 35 °C for 2 h,
C: 4 h after 1,000 Gy X-rays irradiation.