Laboratory of Tumor Biogenesis - 京都大学ウイルス研究所

Apoptosis, or programmed cell death, plays an important role in many biological processes,
including embryogenesis, development of immune system, maintenance of tissue homeostasis, and
elimination of virus-infected and tumor cells. We found cell surface Fas antigen (Fas), which can
directly mediate apoptosis-inducing signals into cells by stimulation with agonistic anti-Fas mAbs
or Fas ligand. Our main research project is to understand the intracellular signal transduction
mechanism of cell death including apoptosis and caspase-independent novel types of cell death, and
the biological significance/physiological role of cell death and cell death-regulating molecules.
Investigations of molecular mechanisms and physiological roles of cell death are important for a
better understanding of mammalian immune system, embryogenesis and tumorigenesis.
Identification of functional regions defining different activity between caspase-3 and
caspase-7 within cells: H. NAKATSUMI and S. YONEHARA
Caspases are central to apoptosis, and the principal executioner caspases, caspase-3 and
caspase-7, were reported to be similar in activity, primary structure and 3-dimensional structure.
Here we identified different activity between caspase-3 and caspase-7 within cells and examined the
relationship between their structure and function by using human cells expressing almost equal
amounts of exogenous caspase-3, caspase-7 and/or chimeric constructs after downregulation of
endogenous caspase-3 and caspase-7 expression. Caspase-3, produced in human cells, showed
much stronger cleaving activity than caspase-7 against a low molecular weight substrate in vitro
dependent on four specific amino acid regions. Within cells, however, additional three regions were
required for caspase-3 to exert much stronger protease activity than caspase-7 against cellular
substrates. Three of the former four regions and the latter three regions were shown to form two
different 3-dimensional structures that located at the interface of the homo-dimer of procaspase-7
on opposite sides. In addition, procaspase-3 and 7 revealed specific homo-dimer-forming activity
within cells dependent on five amino acid regions, which were included in the regions critical to the
cleaving activity within cells. Thus human caspase-3 and 7 exhibit differences in protease activity,
specific homo-dimer-forming activity and 3-dimensional structural features, all of which are closely
Proapoptotic regulator Fas and Bim co-operatively play an important role in
regulation of systemic autoimmune disease: S. TAKAHASHI, P. BOUILLET, A.
Apoptosis has an important role to control development, morphogenesis, and
homeostasis in multicellular organisms. There are two different pathways inducing apoptosis; the
membrane death receptor-mediated extrinsic pathway and the mitochondria-mediated intrinsic
pathway. Fas is one of the most important membrane death receptor, which is essential for
maintenance of immune system as shown in lpr and gld mice whit mutation in Fas and Fas ligand
genes, respectively. On the other hand, the mitochondrial pathway also has a significant role to keep
homeostasis in immune system as demonstrated by Bim or Bax/Bak knockout mice, both of which
show severe defects in immune homeostasis. We have produced Fas and Bim double knockout mice
in C57BL/6 background to reveal whether apoptosis is necessary and/or sufficient for preventing
development of systemic autoimmune disease. Importantly, C57BL/6 mice have been shown to
never develop glomerulonephritis by a single mutation in Fas or Bim gene. We show that Fas/Bim
double knockout mice suffer from glomerulonephritis even in C57BL/6 background. While splenic
T cells from wild-type C57BL/6 mice are deleted after 5 days administration of the superantigen
SEB, splenic T cells from Fas/Bim double knockout C57BL/6 mice were not deleted after 5 days
administration of SEB. These results indicate that proapoptotic regulators Fas and Bim
co-operatively play an important role in elimination of activated peripheral T cells, by which Fas
and Bim would co-operatively regulate immune tolerance.
Novel caspase-independent cell death by downregulation of eEF1A1/EF-1α
expression in tetraploids with chromosome aberrations: Y. KOBAYASHI and S.
When duplicated sister chromatids are not properly compacted in mitosis, chromosomes
are mis-segregated, inducing tetraploidy known to facilitate aneuploid malignancies. We show that
tetraploid cells produced by impaired chromosomal condensation are generally eliminated by a
novel type of cell death different from caspase-dependent apoptosis, while a small proportion of the
tetraploid cells is eliminated by p53-dependent apoptosis. The novel type of caspase-independent
cell death was associated with down-regulated expression of eukaryotic translation elongation
factor 1 alpha 1 (eEF1A1/EF-1α), one of the typical housekeeping gene products, and the cell death
was shown to be inhibited by expression of exogenous eEF1A1. In addition, the downregulation of
eEF1A1 expression was associated with accumulation of its mRNA in Processing bodies (P bodies).
Importantly, expression of exogenous eEF1A1 in normally growing cells was shown to
significantly increase the number of spontaneously arising binucleated cells. Taken together, the
novel cell death machinery should help to eliminate abnormal tetraploid cells.
An essential role of Wnt8a signals in the mesoderm induction of mouse ES cells: A.
Wnt signals were reported to play an important role in mesoderm induction at the
gastrulation stage during embryogenesis. We have been studying a role of the Wnt signals in the
differentiation process of ES cells. Among Wnt family members, Wnt8a as well as Wnt3 were
identified as signaling molecules essential for the mesoderm induction. As little has been reported
about a role of Wnt8a, we are focusing on the analysis of its function.
Knock down of Wnt8a expression by introducing the siRNAs repressed the expression of
Wnt3 and Brachyury, one of the key transcription factors for the mesoderm induction. However,
knock down of Wnt3 also resulted in the repression of Wnt8a as well as Brachyury expression.
Thus, it is likely that Wnt8a and Wnt3 mutually activate their expression and that either or both of
them activate the Brachyury expression. In situ hybridization experiments revealed that all of Wnt3,
Wnt8a, and Brachyury are expressed at a localized area of embryoid bodies, aggregates of
differentiated ES cells. Since the expression pattern of Brachyury is more similar to that of Wnt8a
than to that of Wnt3, Wnt8a seems to be mainly responsible for the Brachyury expression.
Department of Viral Oncology
Laboratory of Tumor Biogenesis
Kamijuku, H, Nagata, Y, Jiang, X, Ichinohe, T, Tashiro, T, Mori, K, Taniguchi, M, Hase, K, Ohno,
H, Shimaoka, T, Yonehara, S, Odagiri, T, Tashiro, M, Sata, T, Hasegawa, H, and Seino, K.I.
Mechanism of NKT cell activation by intranasal coadministration of alpha-galactosylceramide,
which can induce cross-protection against influenza viruses. Mucosal Immunol. 1, 208-218,
Kobayashi, Y, and Yonehara, S. Novel cell death by downregulation of eEF1A1 expression in
tetraploids. Cell Death Differ, advance online publication, September 26, 2008.
Yonehara, S: Novel caspase-independent cell death by downregulation of eEF1A1/EF-1α
expression in tetraploids with chromosomal aberrations. The 15th East Asia Joint Conference
on Biomedical Research. Seoul, Korea, July 20-23, 2008.
Yonehara, S: Physiological roles of Fas. Independent Symposium: Future Prospective New
Drug, MEDICAL-EXPO 2008 in APLAR’s World: The 13th Congress of the Asia Pacific
League of Associations for Rheumatology, Yokohama, September 23-26, 2008.
Yonehara, S: Novel types of cell death identified in 1989 and 2008. Argenes Sponsored
Symposium:Apoptotic Therapy in RA, MEDICAL-EXPO 2008 in APLAR’s World: The 13th
Congress of the Asia Pacific League of Associations for Rheumatology, Yokohama,
September 23-26, 2008.
Yonehara, S: A novel type of caspase-independent cell death in tetraploids with chromosome
aberrations. International Symposium 7: Cell death and autophagy, The 38th Annual Meeting
of the Japanese Society for Immunology, Kyoto, December 1-3, 2008.
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