CALM Depletion Abolishes Endocytosis of HA-Tagged VAMPs
(A) Effect of CALM depletion on surface expression of HA-tagged VAMPs. Control and siRNA-treated cells expressing HA-tagged VAMP2, VAMP3, or VAMP8 were mixed together, fixed without permeabilization, and labeled with anti-HA, then permeabilized and labeled with anti-CALM. Knocking down CALM increases the surface expression of all three VAMPs. The scale bar represents 20 μm.
(B) Endocytosis of anti-HA in cells expressing HA-tagged VAMPs. Antibody was bound to the cells at 4°C, then the cells were warmed to 37°C for 2–30 min and antibody remaining at the cell surface was quantified by flow cytometry. Each point is derived from at least three separate experiments; the error bars show the SEM. Knocking down CALM effectively abolishes the uptake of all three VAMPs. The specificity of the knockdown phenotype was demonstrated by stably transfecting VAMP8-HA-expressing cells with siRNA-resistant myc-tagged CALM (CALMres wt) and knocking down endogenous CALM. Expression of the CALM construct almost completely rescues the knockdown phenotype.
See also Figure S1.