The membrane protein CD9/DRAP 27 potentiates the juxtacrine growth factor activity of the membrane-anchored heparin-binding EGF-like growth factor.
The membrane-anchored heparin-binding EGF-like growth factor precursor (proHB-EGF)/diphtheria toxin receptor (DTR) belongs to a class of transmembrane growth factors and physically associates with CD9/DRAP27 which is also a transmembrane protein. To evaluate the biological activities of proHB-EGF/DTR as a juxtacrine growth factor and the biological significance of its association with CD9/DRAP27, the mitogenic activity of proHB-EGF/DTR was analyzed using stable transfectants of mouse L cells expressing both human proHB-EGF/DTR and monkey CD9/DRAP27, or either one alone. Juxtacrine activity was assayed by measuring the ability of cells in co-culture to stimulate DNA synthesis in an EGF receptor ligand dependent cell line, EP170.7. LH-2 cells expressing human proHB-EGF/DTR stimulated EP170.7 cell growth moderately. However, LCH-1 cells, a stable co-transfectant expressing both human proHB-EGF/DTR and monkey CD9/DRAP27 cDNAs, dramatically unregulated the juxtacrine growth factor activity of proHB-EGF/DTR approximately 25 times over that of LH-2 cells even though both cell types expressed similar levels of proHB-EGF/DTR on the cell surface. Anti-CD9/DRAP27 antibodies which were not able to neutralize the mitogenic activity of soluble HB-EGF suppressed LCH-1 cell juxtacrine growth activity to the same extent as did anti-HB-EGF neutralizing antibodies and CRM 197, specific inhibitors of human HG-EGF. These findings suggest that optimal expression of the juxtacrine growth activity of proHB-EGF/DTR requires co-expression of CD9/DRAP27. These studies also indicate that growth factor potentiation effects which have been observed previously for soluble growth factors also occurs at the level of cell surface associated growth factors.
Higashiyama
S
S
Department of Biochemistry, Osaka University Medical School, Japan.
Iwamoto
R
R
Goishi
K
K
Raab
G
G
Taniguchi
N
N
Klagsbrun
M
M
Mekada
E
E
D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000096:biosynthesis*; D015152:Blotting, Northern; D015153:Blotting, Western; D002450:Cell Communication; D002478:Cells, Cultured; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics; D005434:Flow Cytometry; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D008938:Mitosis / Q000187:drug effects; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D011498:Protein Precursors / Q000096:biosynthesis* / Q000235:genetics; D011956:Receptors, Cell Surface / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D060245:Tetraspanin 29; D016211:Transforming Growth Factor alpha / Q000096:biosynthesis; D015854:Up-Regulation
D015703:Antigens, CD; C554869:CD9 protein, human; C554870:Cd9 protein, mouse; C587883:HBEGF protein, human; C587884:Hbegf protein, mouse; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011498:Protein Precursors; D011956:Receptors, Cell Surface; D060245:Tetraspanin 29; D016211:Transforming Growth Factor alpha; C052268:protransforming growth factor alpha; D066246:ErbB Receptors