Fig. 7.

CD81 but not CD9 overexpression specifically increases surface levels of αvβ5 integrin receptors. Cells transfected with empty plasmid (p), CD81 or CD9 expression plasmids as indicated, (tf:) were either incubated live on ice with antibodies to receptor proteins for live surface IPs (left 3 lanes) or lysed and subjected to total lysate IP (right 3 lanes). Live surface and total lysate IPs were analyzed on the same gel and immunoblotted. Antibodies used for IP and immunoblotting detection are indicated to the left of each panel (IP>blot:). The experiment was performed four times independently. Band intensities of tetraspanin-overexpressing cells were compared with band intensities obtained from empty plasmid controls for each experiment and results averaged. CD81 transfection significantly (P<0.05) increased surface CD81 by 58±13%, total CD81 by 83±11%, surface αv by 36±5%, and surface β5 by 31±9% (mean ± s.d., all n=4). All other bands did not differ significantly from control IPs (average change <10%, P>0.05). Non-specific antibodies did not isolate any of the proteins tested in surface or lysate IPs (data not shown).