[Isoform 1]: 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.; [Isoform 2]: 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. 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. Ca(2+)-regulated dynein adapter protein that activates dynein-mediated transport and dynein-dynactin motility on microtubules and regulates endosomal trafficking of CD47. 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. 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. Plays a role in T-helper 1 (Th1) cell differentiation and T-helper 17 (Th17) cell effector function. Plays a role in store-operated Ca(2+) entry (SOCE) in T-cells by regulating CRAC channel activation.