SDPR induces membrane curvature and functions in the formation of caveolae.
Bottom Line: STB colocalizes extensively with both SDPR and caveolin 1.Loss of caveolae reduces the propensity of STB to induce membrane tubulation.We conclude that SDPR is a membrane-curvature-inducing component of caveolae, and that STB-induced membrane tubulation is facilitated by caveolae.
Affiliation: MRC-LMB, Cambridge, UK.
Caveolae are plasma membrane invaginations with a characteristic flask-shaped morphology. They function in diverse cellular processes, including endocytosis. The mechanism by which caveolae are generated is not fully understood, but both caveolin proteins and PTRF (polymerase I and transcript release factor, also known as cavin) are important. Here we show that loss of SDPR (serum deprivation protein response) causes loss of caveolae. SDPR binds directly to PTRF and recruits PTRF to caveolar membranes. Overexpression of SDPR, unlike PTRF, induces deformation of caveolae and extensive tubulation of the plasma membrane. The B-subunit of Shiga toxin (STB) also induces membrane tubulation and these membrane tubes also originate from caveolae. STB colocalizes extensively with both SDPR and caveolin 1. Loss of caveolae reduces the propensity of STB to induce membrane tubulation. We conclude that SDPR is a membrane-curvature-inducing component of caveolae, and that STB-induced membrane tubulation is facilitated by caveolae.
Related in: MedlinePlus
Mentions: Tubular membrane structures have been implicated in the endocytosis of the B-subunit of shiga toxin (STB), and STB induces extensive membrane tubulation in energy-depleted cells 12, 14. As it is unknown whether cytosolic or membrane proteins participate in the formation of these tubes, we asked whether they could be related to the tubes induced by SDPR over-expression. When HeLa cells over-expressing SDPR-GFP were depleted of ATP and labeled with STB there was a high degree of co-localization between STB and SDPR in both tubes and membrane puncta (Figure 6A). Comparing cells expressing the same amount of SDPR-GFP, the number and appearance of SDPR-positive tubes was not altered by the combination of energy poisons and STB (Supplementary Figure 5C). This implies that although STB induces formation of tubes in energy depleted, non-transfected cells 12, when SDPR tubes are already present STB may preferentially enter these tubes.