Summary of Research Project Results under JSPS FY2001
"Research for the Future Program"

1.Research Institution Osaka University
2.Research Area Life Sciences
3.Research Field Cellular Signaling
4.Term of Project FY1997 〜 FY2001
5.Project Number 97L00303
6.Title of Project Growth signaling transmitted by cell adhesion

7.Project Leader
Name Institution,Department Title of Position
Eisuke Mekada Osaka University, Research Institute for Microbial Diseases Professer

8.Core Members

Names Institution,Department Title of Position
Ryo Iwamoto Osaka University, Research Institute for Microbial Diseases Assistant Professer
Kenji Miyado Osaka University, Research Institute for Microbial Diseases Research Associate
Hiroto Mizushima Osaka University, Research Institute for Microbial Diseases Research Fellow

9.Summary of Research Results

Heparin-binding EGF-like growth factor (HB-EGF) is a member of the EGF family of growth factors, which interact with EGF receptor to exert mitogenic activity. This factor is synthesized as a membrane-anchored precursor protein (proHB-EGF) and then cleaved on the cell surface to yield soluble growth factor. ProHB-EGF is not only a precursor for the soluble form but also for the biologically active molecule, providing growth regulation to neighboring cells in a juxtacrine mode. ProHB-EGF forms a complex with other membrane proteins including CD9 and integrin α3β1. CD9, a tetra membrane-spanning protein, upregulates the juxtacrine mitogenic activity of proHB-EGF but not the mitogenic activity of the soluble form of HB-EGF. Integrin α3β1 is known to bind several extracellular matrix proteins including laminin 5, but the significance of the association with proHB-EGF has not been understood. ProHB-EGF-CD9-Integrin α3β1 complex is co-localized at cell-cell contact sites, suggesting that this protein complex may play some roles in intercellular signaling among neighboring cells.
In order to know the biological functions and physiological role of HB-EGF and its associating molecules, we have studied the following experiments: 1) in vitro assay of the growth inhibitory activity of proHB-EGF, 2) studies with mutant mice lacking HB-EGF or CD9 gene, 3) mechanism for the ectodomain shedding of proHB-EGF, 4) integrin-tetraspanin comlex formation. Results indicates that strict control of proHB-EGF ectodomain shedding is essential for the proper function of this growth
factor. Deregulated proHB-EGF shedding in mice results in severe hyperplastic and developmental abnormalities. In order to know the physiological activity of CD9, mice lacking CD9 were produced. Results showed that CD9 is a crucial factor for mouse oocytes in fertilization.

10.Key Words

(1)HB-EGF、(2)EGF receptor、(3)transactivation
(4)targeting mouse、(5)Knockout mice、(6)CD9
(7)Fertilization、(8)cell growth