The differentiation of cells depends on a precise control of their internal organization, which is the result of a complex dynamic interplay between the cytoskeleton, molecular motors, signaling molecules, and membranes. For example, in the developing neuron, the protein ADAP1 (ADP-ribosylation factor GTPase-activating protein [ArfGAP] with dual pleckstrin homology [PH] domains 1) has been suggested to control dendrite branching by regulating the small GTPase ARF6. Together with the motor protein KIF13B, ADAP1 is also thought to mediate delivery of the second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP3) to the axon tip, thus contributing to PIP3 polarity. However, what defines the function of ADAP1 and how its different roles are coordinated are still not clear. Here, we studied ADAP1’s functions using in vitro reconstitutions. We found that KIF13B transports ADAP1 along microtubules, but that PIP3 as well as PI(3,4)P2 act as stop signals for this transport instead of being transported. We also demonstrate that these phosphoinositides activate ADAP1’s enzymatic activity to catalyze GTP hydrolysis by ARF6. Together, our results support a model for the cellular function of ADAP1, where KIF13B transports ADAP1 until it encounters high PIP3/PI(3,4)P2 concentrations in the plasma membrane. Here, ADAP1 disassociates from the motor to inactivate ARF6, promoting dendrite branching.
We thank Urban Bezeljak, Natalia Baranova, Mar Lopez-Pelegrin, Catarina Alcarva, and Victoria Faas for sharing reagents and helpful discussions. We thank Veronika Szentirmai for help with protein purifications. We thank Carrie Bernecky, Sascha Martens, and the M.L. lab for comments on the manuscript. We thank the bioimaging facility, the life science facility, and Armel Nicolas from the mass spec facility at the Institute of Science and Technology (IST) Austria for technical support. C.D. acknowledges funding from the IST fellowship program; this work was supported by Human Frontier Science Program Young Investigator Grant RGY0083/2016.
Düllberg CF, Auer A, Canigova N, Loibl K, Loose M. In vitro reconstitution reveals phosphoinositides as cargo-release factors and activators of the ARF6 GAP ADAP1. PNAS. 2021;118(1). doi:10.1073/pnas.2010054118
Düllberg, C. F., Auer, A., Canigova, N., Loibl, K., & Loose, M. (2021). In vitro reconstitution reveals phosphoinositides as cargo-release factors and activators of the ARF6 GAP ADAP1. PNAS. National Academy of Sciences. https://doi.org/10.1073/pnas.2010054118
Düllberg, Christian F, Albert Auer, Nikola Canigova, Katrin Loibl, and Martin Loose. “In Vitro Reconstitution Reveals Phosphoinositides as Cargo-Release Factors and Activators of the ARF6 GAP ADAP1.” PNAS. National Academy of Sciences, 2021. https://doi.org/10.1073/pnas.2010054118.
C. F. Düllberg, A. Auer, N. Canigova, K. Loibl, and M. Loose, “In vitro reconstitution reveals phosphoinositides as cargo-release factors and activators of the ARF6 GAP ADAP1,” PNAS, vol. 118, no. 1. National Academy of Sciences, 2021.
Düllberg CF, Auer A, Canigova N, Loibl K, Loose M. 2021. In vitro reconstitution reveals phosphoinositides as cargo-release factors and activators of the ARF6 GAP ADAP1. PNAS. 118(1), e2010054118.
Düllberg, Christian F., et al. “In Vitro Reconstitution Reveals Phosphoinositides as Cargo-Release Factors and Activators of the ARF6 GAP ADAP1.” PNAS, vol. 118, no. 1, e2010054118, National Academy of Sciences, 2021, doi:10.1073/pnas.2010054118.
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