Analysis of GPIb and GPIX in Chinese hamster ovary (CHO)  IX cells transiently transfected with GPIbβ.

(A) CHOαIX cells expressing GPIbα and GPIX were additionally transfected with wild-type GPIbβ or the mutant W21stop-GPIbβ or were mock transfected with the expression plasmid alone. GPIbα was readily detectable in cells transfected with plasmid alone (shaded area), the mutant W21stop-GPIbβ (thin lines), or wild-type GPIbβ (boldface lines). (B) There was a significant increase in the surface expression of GPIX when wild-type GPIbβ (boldface lines) was transfected into CHOαIX cells compared with mock-transfected controls (shaded area) or cells transfected with the mutant W21stop-GPIbβ (thin line). (C) CHOαIX cells transfected with wild-type GPIbβ (boldface lines) were allowed to react with the complex-specific antibody AK1. Again, there was a marked increase in surface fluorescence compared with either the mock-transfected cells (shaded area) or the cells transfected with W21stop-GPIbβ (thin lines). Thus, the mutant GPIbβ failed to support the efficient expression of the GPIbα-IX complex on the surface of these cells.