


Keiichi Nakayama | Last modified date:2022.06.25 |

Graduate School
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Homepage
https://kyushu-u.pure.elsevier.com/en/persons/keiichi-nakayama
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http://www.bioreg.kyushu-u.ac.jp/saibou/index_en.html
https://www.bioreg.kyushu-u.ac.jp/saibou/index_en.html
Phone
092-642-6815
Fax
092-642-6819
Academic Degree
M.D., Ph.D.
Country of degree conferring institution (Overseas)
No
Field of Specialization
Proteolysis to regulate cell cycle
Total Priod of education and research career in the foreign country
05years06months
Outline Activities
Research Project:Investigation into the molecular mechanism of cell-growth and cell-death control.
1. Elucidation of physiological function of p27Kip1 that controls cell growth and differentiation
Growth and death are the basic properties of the cell. Disturbance of the control for cell growth and death has been believed as a major cause of carcinogenesis. Cell growth and death do not always take place, rather they are tightly regulated in tissue- and development-specific manners. For example, neurons proliferate only in fetus, but never in adult. The mechanism of this development-specific regulation of cell growth has been largely unclear.
We investigate the physiological roles of factors which control cell cycle and cell death. Recently we focus our interest on the roles of cyclin-dependent-kinase inhibitors (CKI), which negatively regulate cell proliferation, in development and carcinogenesis. Mice lacking p27Kip1, which is the most related CKI to development and growth regulation, were created in our laboratory. The p27Kip1 knockout mice displayed increased body size, and multiple organ hyperplasia in immune, nervous, and reproductive systems. In addition, pituitary tumor frequently arose in these knockout mice, indicating that p27Kip1 is an oncosuppressor molecule. A series of clinical studies suggested that tumors with lower expression of p27Kip1 have poorer prognosis. Thus, we explore the molecular mechanism by which expression level of p27Kip1 is controlled.
2. Elucidation of the molecular mechanism for ubiquitination of p27Kip1
The ubiquitin-proteasome pathway of protein degradation plays an important role in control of the abundance of short-lived regulatory proteins. The ubiquitin-attachment system consists of several components that act in concert. A ubiquitin-activating enzyme (E1) uses ATP to form a thioester bond between itself and ubiquitin, and it then transfers the activated ubiquitin to a ubiquitin-conjugating enzyme (E2). Protein-ubiquitin ligation often requires the participation of a third component, termed ubiquitin ligase (E3). Although the E3 components are thought to be primarily responsible for substrate recognition, they are the least well understood of the enzymes of the ubiquitin-conjugation system.
The SCF complexes, a major class of E3 ligases, consist of the invariable components Skp1, Cul1, and Rbx1/ROC1 as well as a variable component, known as an F-box protein, that binds to Skp1 through its F-box motif and serves as the substrate-recognition subunit. Skp2, an F-box protein with leucine-rich repeats, mediates degradation of p27Kip1.
With the use of gene targeting in embryonic stem (ES) cells, we have now generated mice lacking Skp2. Cells derived from these animals exhibit hyperaccumulation of both cyclin E and p27Kip1, polyploidy, and multiple centrosomes. Consistent with these observations, our biochemical analysis indicates that Skp2 mediates ubiquitin-dependent degradation of cyclin E. Taken together, these data suggest that SCFSkp2 functions as the principal ubiquitin ligase in determining the abundance of cell cycle regulatory proteins at the G1-S transition, thereby ensuring strict control of chromosomal replication and centrosome duplication.
1. Elucidation of physiological function of p27Kip1 that controls cell growth and differentiation
Growth and death are the basic properties of the cell. Disturbance of the control for cell growth and death has been believed as a major cause of carcinogenesis. Cell growth and death do not always take place, rather they are tightly regulated in tissue- and development-specific manners. For example, neurons proliferate only in fetus, but never in adult. The mechanism of this development-specific regulation of cell growth has been largely unclear.
We investigate the physiological roles of factors which control cell cycle and cell death. Recently we focus our interest on the roles of cyclin-dependent-kinase inhibitors (CKI), which negatively regulate cell proliferation, in development and carcinogenesis. Mice lacking p27Kip1, which is the most related CKI to development and growth regulation, were created in our laboratory. The p27Kip1 knockout mice displayed increased body size, and multiple organ hyperplasia in immune, nervous, and reproductive systems. In addition, pituitary tumor frequently arose in these knockout mice, indicating that p27Kip1 is an oncosuppressor molecule. A series of clinical studies suggested that tumors with lower expression of p27Kip1 have poorer prognosis. Thus, we explore the molecular mechanism by which expression level of p27Kip1 is controlled.
2. Elucidation of the molecular mechanism for ubiquitination of p27Kip1
The ubiquitin-proteasome pathway of protein degradation plays an important role in control of the abundance of short-lived regulatory proteins. The ubiquitin-attachment system consists of several components that act in concert. A ubiquitin-activating enzyme (E1) uses ATP to form a thioester bond between itself and ubiquitin, and it then transfers the activated ubiquitin to a ubiquitin-conjugating enzyme (E2). Protein-ubiquitin ligation often requires the participation of a third component, termed ubiquitin ligase (E3). Although the E3 components are thought to be primarily responsible for substrate recognition, they are the least well understood of the enzymes of the ubiquitin-conjugation system.
The SCF complexes, a major class of E3 ligases, consist of the invariable components Skp1, Cul1, and Rbx1/ROC1 as well as a variable component, known as an F-box protein, that binds to Skp1 through its F-box motif and serves as the substrate-recognition subunit. Skp2, an F-box protein with leucine-rich repeats, mediates degradation of p27Kip1.
With the use of gene targeting in embryonic stem (ES) cells, we have now generated mice lacking Skp2. Cells derived from these animals exhibit hyperaccumulation of both cyclin E and p27Kip1, polyploidy, and multiple centrosomes. Consistent with these observations, our biochemical analysis indicates that Skp2 mediates ubiquitin-dependent degradation of cyclin E. Taken together, these data suggest that SCFSkp2 functions as the principal ubiquitin ligase in determining the abundance of cell cycle regulatory proteins at the G1-S transition, thereby ensuring strict control of chromosomal replication and centrosome duplication.
Research
Research Interests
- Elucidation of mechanisms underlying proteolysis in the cell cycle control
keyword : cell cycle, p27, ubiquitin, knockout mouse
1996.10We have been studying the mechanisms underlying proteolysis of p27 CDK inhibitor. We have created a series of mutant mice lacking the key molecules that are involved in the p27 degradation.. - Study of ubiquitylation in neurodegerative diseases
keyword : polyglutamine disease, SCA3, ataxin-3, ubiquitin, E4B/UFD2a
2001.04Various inherited neurodegenerative diseases result from an increase in the number of glutamine codon repeats within the open reading frame of the responsible gene. The presence of insoluble aggregates in neurons, which have been shown to stain with anti-ubiquitin, is a hallmark of these polyglutamine diseases as well as of many other neurodegenerative disorders. However, neither the significance of these inclusions nor the molecular mechanism of their ubiquitylation has been clear. We have now shown that ataxin-3, the product of the gene responsible for a polyglutamine disease Spinocerebellar ataxia 3 (SCA3), is degraded by the ubiquitin-proteasome pathway. To identify the enzymes that mediate the ubiquitylation of ataxin-3, we partially purified a polyubiquitylation activity for this protein, and found that E4B (a ubiquitin chain assembly factor, or E4) as well as VCP (a AAA-family ATPase) copurified with this polyubiquitylation activity. Significantly, ataxin-3-VCP-E4B formed a trimeric complex, and E4B mediated polyubiquitylation of ataxin-3. Expression of E4B markedly promoted the degradation of an ataxin-3 isoform with an expanded polyglutamine tract, overcoming the resistance to degradation conferred by glutamine repeat expansion. In contrast, functional inhibition of E4B resulted both in a delay in ataxin-3 degradation and in the consequent formation of intracellular aggregates. Finally, we showed that expression of E4B prevented neurodegeneration in transgenic flies expressing an ataxin-3 mutant with an expanded polyglutamine tract. Our data thus provide biochemical and genetic evidence that a mammalian E4 enzyme plays an important role in the degradation of ataxin-3. Our study is one of a few that have recently unveiled the mechanisms of ubiquitylation of proteins involved in neurodegenerative diseases, and it represents the first demonstration that E4 exists in multicellular organisms and contributes to the degradation of a physiological substrate. Targeted expression of E4B is therefore a potential gene therapy for polyglutamine diseases..
- Molecular analysis of the SCF ubiquitin ligase from yeast to human
Reports
1. | Nakayama, K. I., Nakayama, K., Ubiquitin ligases: cell-cycle control and cancer, Nature Rev. Cancer, 2006.05. |
Papers
Educational
Educational Activities
School of Medicine: Immunology
Graduate School of Medicine: Experimental Zoology
Graduate School of Medicine: Molecular Medicine
Other Educational Activities
Graduate School of Medicine: Experimental Zoology
Graduate School of Medicine: Molecular Medicine
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