Ca(2+)-binding protein that plays a key role in store-operated Ca(2+) entry (SOCE) in T-cells by regulating CRAC channel activation. Acts as a cytoplasmic calcium-sensor that facilitates the clustering of ORAI1 and STIM1 at the junctional regions between the plasma membrane and the endoplasmic reticulum upon low Ca(2+) concentration. It thereby regulates CRAC channel activation, including translocation and clustering of ORAI1 and STIM1. Upon increase of cytoplasmic Ca(2+) resulting from opening of CRAC channels, dissociates from ORAI1 and STIM1, thereby destabilizing the ORAI1-STIM1 complex. Rab GTPase that mediates the trafficking of Weibel-Palade bodies (WPBs) to microtubule organizing center (MTOC) in endothelial cells in response to acute inflammatory stimuli (PubMed:31092558). During histamine (but not thrombin) stimulation of endothelial cells, the dynein-bound form induces retrograde transport of a subset of WPBs along microtubules to the MTOC in a Ca(2+)-independent manner and its GTPase activity is essential for this function (PubMed:31092558). Ca(2+)-regulated dynein adapter protein that activates dynein-mediated transport and dynein-dynactin motility on microtubules and regulates endosomal trafficking of CD47 (PubMed:30814157). Acts as an intracellular signaling module bridging two important T-cell receptor (TCR) signaling pathways, Ca(2+)-NFAT and JNK, to affect T-cell activation (PubMed:27016526). In resting T-cells, is predominantly localized near TGN network in a GTP-bound form, upon TCR stimulation, localizes at the immunological synapse via interaction with VAV1 to activate downstream Ca(2+)-NFAT and JNK signaling pathways (PubMed:27016526). Plays a role in T-helper 1 (Th1) cell differentiation and T-helper 17 (Th17) cell effector function (PubMed:29987160). Plays a role in store-operated Ca(2+) entry (SOCE) in T-cells by regulating CRAC channel activation (PubMed:27016526). Interacts with ORAI1 and STIM1; the interaction is direct and takes place in absence of Ca(2+). Forms a complex with ORAI1 and STIM1 at low concentration of Ca(2+), the complex dissociates at elevated Ca(2+) concentrations. Interacts with ORAI2 and ORAI3. Interacts with DYNC1H1 (PubMed:31092558). Interacts with the dynein-dynactin complex in a Ca(2+)-dependent manner (PubMed:30814157). Interacts with VAV1 (PubMed:27016526). T-cell activation-induced elevation of intracellular of Ca(2+) stimulates its transport toward the microtubule organizing center (MTOC) (PubMed:30814157). Histamine stimulation induces a trafficking to the MTOC in a GTP-binding-dependent but Ca(2+)-binding-independent manner (PubMed:31092558). Localizes to Golgi membrane in resting T-cells and upon its interaction with VAV1, is translocated from the Golgi membrane to the immunological synapse via subsynaptic vesicles (PubMed:27016526). Its localization in the Golgi membrane requires isoprenylation and GTP-binding (PubMed:27016526). Expressed in the Jurkat T-cell line. Expressed in endothelial cells (PubMed:25475730). Expressed in Weibel-Palade bodies (which are P-selectin/SELP negative) in endothelial cells (PubMed:31092558). Expressed in the Jurkat T-cell line (PubMed:30814157, PubMed:27016526). Belongs to the EFCAB4 family.