CANCER MEDICINE AND BIOPHYSICS DIVISION

6.CANCER MEDICINE AND BIOPHYSICS DIVISION

    Programmed cell deaths (PCDs) represented by apoptosis play essential roles in the maintenance of homeostasis in multicellular organisms. Therefore, disruption of the control mechanisms of PCDs may give rise to various pathological conditions. For instance, PCDs are known to function as a defense mechanism against cancer through elimination of potentially neoplastic cells with genetic abnormalities including deregulated oncogene activation, and inactivation of PCD is a critical step for cancer cells to survive and grow to become clinically significant tumors. It is therefore expected that understanding how PCDs are regulated as well as how they are modulated in cancer cells should provide beneficial clues to designing preventive and/or therapeutic strategies against cancer. Thus, in the Biophysics Division, studies on the molecular mechanism of PCD regulation have been conducted.
The Role of Caspase-independent Non-apoptotic Programmed Cell Death in Tumor Suppression

    Recent evidence indicates that PCDs can be divided largely into two categories according to their dependence on caspases for regulation. Pharmacological inhibitors of caspases are useful experimental tools for determining caspase dependence of cell death models of interest. ZAsp-CH2-DCB is one of the most widely used pan-caspase inhibitors for the purpose, but a cellular mechanism was identified which inactivates this pan-caspase inhibitor in a reversible manner and may cause misinterpretation of caspase dependence ⁽¹¹⁰⁾.
    In contrast to apoptotic PCD regulated by caspases, the role of caspase-independent, non-apoptotic PCD in tumor suppression remained to be established. The possible role of Ras-mediated non-apoptotic PCD in the spontaneous regression of neuroblastoma was therefore investigated ⁽¹¹¹⁾. Immunohistochemical and electron microscopic analyses of tumor samples obtained from neuroblastoma patients revealed that tumor cells with Ras overexpression undergo non-apoptotic cell death with features of autophagic degeneration in the absence of caspase activation and that such Ras-associated non-apoptotic cell death occurs more frequently in neuroblastomas with higher possibilities of spontaneous regression. In vitro experiments indicated that transfection-mediated Ras expression in neuroblastoma cells causes cell death with features observed in Ras-associated non-apoptotic cell death in neuroblastoma tissues. Thus, it was strongly suggested that Ras-mediated non-apoptotic PCD plays an important role in neuroblastoma regression.
    The Akt protein kinase is one of the representative onco-proteins activated in a variety of human cancers. In addition to its well-documented anti-apoptotic function, Akt was recently shown to inhibit ceramide-induced non-apoptotic death of glioma cells which requires neither caspases nor mitochondrial membrane permeabilization ⁽¹¹²⁾. This may imply that suppression of non-apoptotic as well as apoptotic PCD is essential for tumorigenesis.
The Lon Protease

    Multiple lines of evidence for involvement of ATP-dependent proteases in the quality control of intracellular proteins have been recently reported. In the Biophysics Division, structural and functional analyses of the Lon protease have been in progress, since Lon degrades abnormal proteins such as denatured proteins in an ATP-dependent manner, has the simplest structural organization among the ATP-dependent proteases (a multimer of a single subunit that has both ATPase and protease activities), and is conserved from prokaryotes to higher eukaryotes. The cleavage pattern of its physiological substrate SulA protein by Escherichia coli Lon protease was examined in detail, and the cleavage sites as well as the role of ATP hydrolysis in Lon-mediated SulA cleavage were elucidated. ⁽¹¹³⁾. The gene structure, the protein structure, and function of bromelain inhibitor, one of the cystein protease inhibitors from pineapple, were also examined ⁽¹¹⁴⁾.




6.CANCER MEDICINE AND BIOPHYSICS DIVISION



	Programmed cell deaths (PCDs) represented by apoptosis play essential roles in the maintenance of homeostasis in multicellular organisms. Therefore, disruption of the control mechanisms of PCDs may give rise to various pathological conditions. For instance, PCDs are known to function as a defense mechanism against cancer through elimination of potentially neoplastic cells with genetic abnormalities including deregulated oncogene activation, and inactivation of PCD is a critical step for cancer cells to survive and grow to become clinically significant tumors. It is therefore expected that understanding how PCDs are regulated as well as how they are modulated in cancer cells should provide beneficial clues to designing preventive and/or therapeutic strategies against cancer. Thus, in the Biophysics Division, studies on the molecular mechanism of PCD regulation have been conducted. The Role of Caspase-independent Non-apoptotic Programmed Cell Death in Tumor Suppression Recent evidence indicates that PCDs can be divided largely into two categories according to their dependence on caspases for regulation. Pharmacological inhibitors of caspases are useful experimental tools for determining caspase dependence of cell death models of interest. ZAsp-CH2-DCB is one of the most widely used pan-caspase inhibitors for the purpose, but a cellular mechanism was identified which inactivates this pan-caspase inhibitor in a reversible manner and may cause misinterpretation of caspase dependence ⁽¹¹⁰⁾. In contrast to apoptotic PCD regulated by caspases, the role of caspase-independent, non-apoptotic PCD in tumor suppression remained to be established. The possible role of Ras-mediated non-apoptotic PCD in the spontaneous regression of neuroblastoma was therefore investigated ⁽¹¹¹⁾. Immunohistochemical and electron microscopic analyses of tumor samples obtained from neuroblastoma patients revealed that tumor cells with Ras overexpression undergo non-apoptotic cell death with features of autophagic degeneration in the absence of caspase activation and that such Ras-associated non-apoptotic cell death occurs more frequently in neuroblastomas with higher possibilities of spontaneous regression. In vitro experiments indicated that transfection-mediated Ras expression in neuroblastoma cells causes cell death with features observed in Ras-associated non-apoptotic cell death in neuroblastoma tissues. Thus, it was strongly suggested that Ras-mediated non-apoptotic PCD plays an important role in neuroblastoma regression. The Akt protein kinase is one of the representative onco-proteins activated in a variety of human cancers. In addition to its well-documented anti-apoptotic function, Akt was recently shown to inhibit ceramide-induced non-apoptotic death of glioma cells which requires neither caspases nor mitochondrial membrane permeabilization ⁽¹¹²⁾. This may imply that suppression of non-apoptotic as well as apoptotic PCD is essential for tumorigenesis. The Lon Protease Multiple lines of evidence for involvement of ATP-dependent proteases in the quality control of intracellular proteins have been recently reported. In the Biophysics Division, structural and functional analyses of the Lon protease have been in progress, since Lon degrades abnormal proteins such as denatured proteins in an ATP-dependent manner, has the simplest structural organization among the ATP-dependent proteases (a multimer of a single subunit that has both ATPase and protease activities), and is conserved from prokaryotes to higher eukaryotes. The cleavage pattern of its physiological substrate SulA protein by Escherichia coli Lon protease was examined in detail, and the cleavage sites as well as the role of ATP hydrolysis in Lon-mediated SulA cleavage were elucidated. ⁽¹¹³⁾. The gene structure, the protein structure, and function of bromelain inhibitor, one of the cystein protease inhibitors from pineapple, were also examined ⁽¹¹⁴⁾.