Remodelling of the actin cytoskeleton in response to external stimuli is obligatory for many cellular processes in the amoebic cell. A rapid and local rearrangement of the actin cytoskeleton is required for the development of the cellular protrusions during phagocytosis, trogocytosis, migration, and invasion. Here, we demonstrated that EhC2B, a C2 domain-containing protein, is an actin modulator. EhC2B was first identified as an effector of EhRab21 from E. histolytica. In vitro interaction studies including GST pull-down, fluorescence-based assay and ITC also corroborated with our observation. In the amoebic trophozoites, EhC2B accumulates at the pseudopods and the tips of phagocytic cups. FRAP based studies confirmed the recruitment and dynamics of EhC2B at the phagocytic cup. Moreover, we have shown the role of EhC2B in erythrophagocytosis. It is well known that calcium-dependent signal transduction is essential for the cytoskeletal dynamics during phagocytosis in the amoebic parasite. Using liposome pelleting assay, we demonstrated that EhC2B preferentially binds to the phosphatidylserine in the presence of calcium. The EhC2B mutants defective in calcium or lipid-binding failed to localise beneath the plasma membrane. The cells overexpressing these mutants have also shown a significant reduction in erythrophagocytosis. The role of EhC2B in erythrophagocytosis and pseudopod formation was also validated by siRNA-based gene knockdown approach. Finally, with the help of in vitro nucleation assay using fluorescence spectroscopy and total internal reflection fluorescence microscopy, we have established that EhC2B is an actin nucleator. Collectively, based on the results from the study, we propose that EhC2B acts like a molecular bridge which promotes membrane deformation via its actin nucleation activity during the progression of the phagocytic cup in a calcium-dependent manner.

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ARL5B, an ARF‐like small GTPase localized in the trans‐Golgi regulates the transport between the Golgi and endosomes. Besides, ARL5B promotes migration and invasion in breast cancer cells. Although a few interacting partners are identified, the regulators of ARL5B are largely uncharacterized. Here, using GBP‐pull down followed by mass spectrometry, we identified HSC70 (Heat shock cognate protein), as an interacting partner of ARL5B. Further, our pull‐down and ITC based studies suggested that ARL5B is a substrate of HSC70. In addition, our in vitro studies suggested that the N‐terminal of ARL5B is important for recognition by HSC70. Extending our studies in MDA‐MB‐231 cells, we observed that the depletion of HSC70 reduced the localization of ARL5B with Golgi markers. Finally, using in vitro reconstitution approach, we provide evidence that HSC70 facilitates the recruitment of ARL5B to the Golgi membrane. Collectively, our results suggest that the interaction of ARL5B with HSC70 is important for its Golgi localization and, consequently regulates intracellular trafficking in breast cancer cells.