The accurate assembly of signalosomes centered on the adaptor protein LAT (linker of activated T cells) is required for antigen receptor signaling in T cells and mast cells. During signalosome assembly, members of the growth factor receptor-bound protein 2 (Grb2) family of cytosolic adaptor proteins bind cooperatively to LAT through interactions with its phosphorylated tyrosine (pTyr) residues. We demonstrated the Src homology 2 (SH2) domain-mediated dimerization of the Grb2 family member, Grb2-related adaptor downstream of Shc (Gads). Gads dimerization was mediated by an SH2 domain interface, which is distinct from the pTyr binding pocket and which promoted cooperative, preferential binding of paired Gads to LAT. This SH2 domain-intrinsic mechanism of cooperativity, which we quantified by mathematical modeling, enabled Gads to discriminate between dually and singly phosphorylated LAT molecules. Mutational inactivation of the dimerization interface reduced cooperativity and abrogated Gads signaling in T cells and mast cells. The dimerization-dependent, cooperative binding of Gads to LAT may increase antigen receptor sensitivity by reducing signalosome formation at incompletely phosphorylated LAT molecules, thereby prioritizing the formation of complete signalosomes.

Terrestrial lidar technology provides accurate surface data at high spatial resolution. This study examined the ability of lidar scanners to evaluate soil erosion and deposition at high spatial and temporal resolutions. Lidar scans were conducted in six field plots with three different tillage systems during two rain seasons, focusing on four major rainfall events. Results show that the lidar scanner identifies changes in the surface elevation in the case of rill erosion within the furrows. In these cases, the high-quality quantitative data can assist practical decision-making and can contribute to the calibration of physically based erosion models. In other cases, however, the results show that the ability of the lidar scanners to detect erosion and deposition processes is limited. The reasons for this limitation are the minor effect of sheet erosion on flat surfaces and soil swelling and shrinking occurring during and after rainfall events. Swelling-shrinking and soil compaction processes need to be taken into account during lidar scanning, as their magnitude is comparable to that of soil loss by erosion. On the other hand, the ability to measure these processes allows investigation of the dynamics of surface processes during wetting and drying sequences. The results showed also that the effect of the rainfall pattern was stronger when the rainfall intensity and the initial soil moisture were higher, and that rill erosion is more important when the furrows are parallel to the slope direction, while deposition is accentuated when the furrows are perpendicular to the slope.

The costimulatory receptor CD28 synergizes with the TCR to promote IL-2 production, cell survival, and proliferation; yet the obligatory interdependence of TCR and CD28 signaling is not well understood. Upon TCR stimulation, Gads, a Grb2-family adaptor, bridges the interaction of two additional adaptors, LAT and SLP-76, to form a TCR-induced effector signaling complex. SLP-76 binds the Tec-family tyrosine kinase, Itk, which phosphorylates SLP-76 Y173 and PLC-γ1 Y783. In this study, we identified TCR-inducible, Itk-mediated phosphorylation of Gads Y45 in a human T cell line and in mouse primary T cells. Y45 is found within the N-terminal SH3 domain of Gads, an evolutionarily conserved domain with no known signaling function. Gads Y45 phosphorylation depended on the interaction of Gads with SLP-76 and on the dimerization-dependent binding of Gads to phospho-LAT. We provide evidence that Itk acts through SLP-76 and Gads to promote the TCR/CD28–induced activation of the RE/AP transcriptional element from the IL-2 promoter. Two Itk-related features of SLP-76, Y173 and a proline-rich Itk SH3 binding motif on SLP-76, were dispensable for activation of NFAT but selectively required for the TCR/CD28–induced increase in cytoplasmic and nuclear c-Rel and consequent RE/AP activation. We provide evidence that unphosphorylated, monomeric Gads mediates an RE/AP–directed inhibitory activity that is mitigated upon Gads dimerization and Y45 phosphorylation. This study illuminates a new, to our knowledge, regulatory module, in which TCR-induced, Itk-mediated phosphorylation sites on SLP-76 and Gads control the transcriptional response to TCR/CD28 costimulation, thus enforcing the obligatory interdependence of the TCR and CD28 signaling pathways.

The costimulatory receptor, CD28, synergizes with the T cell antigen receptor (TCR) to promote IL-2 production, cell survival and proliferation. Despite their profound synergy, the obligatory interdependence of the signaling pathways initiated by these two receptors is not well understood. Upon TCR stimulation, Gads, a Grb2-family adaptor, bridges the interaction of two additional adaptors, LAT and SLP-76, to form a TCR-induced effector signaling complex. SLP-76 binds the Tec-family tyrosine kinase, Itk, which phosphorylates SLP-76 at Y173 and PLC-γ1 at Y783. Here we identified Gads Y45 as an additional TCR-inducible, Itk-mediated phosphorylation site. Y45 is found within the N-terminal SH3 domain of Gads, an evolutionarily conserved domain with no known binding partners or signaling function. Gads Y45 phosphorylation depended on the interaction of Gads with SLP-76 and on the preferentially-paired binding of Gads to phospho-LAT. Three Itk-related features, Gads Y45, SLP-76 Y173, and a proline-rich Itk SH3-binding motif on SLP-76, were selectively required for activation of the CD28 RE/AP transcriptional element from the IL-2 promoter, but were not required to activate NFAT. This study illuminates a new regulatory module, in which Itk-targeted phosphorylation sites on two adaptor proteins, SLP-76 and Gads, control the transcriptional response to TCR/CD28 costimulation, thus enforcing the obligatory interdependence of the TCR and CD28 signaling pathways.