The engagement of the T-cell receptor (TCR) causes the rapid recruitment of multiple signaling molecules into clusters with the TCR. Upon receptor activation, the adapters LAT and SLP-76, visualized as chimeric proteins tagged with yellow fluorescent protein, transiently associate with and then rapidly dissociate from the TCR. Previously, we demonstrated that after recruitment into signaling clusters, SLP-76 is endocytosed in vesicles via a lipid raft-dependent pathway that requires the interaction of the endocytic machinery with ubiquitylated proteins. In this study, we focus on LAT and demonstrate that signaling clusters containing this adapter are internalized into distinct intracellular compartments and dissipate rapidly upon TCR activation. The internalization of LAT was inhibited in cells expressing versions of the ubiquitin ligase c-Cbl mutated in the RING domain and in T cells from mice lacking c-Cbl. Moreover, c-Cbl RING mutant forms suppressed LAT ubiquitylation and caused an increase in cellular LAT levels, as well as basal and TCR-induced levels of phosphorylated LAT. Collectively, these data indicate that following the rapid formation of signaling complexes upon TCR stimulation, c-Cbl activity is involved in the internalization and possible downregulation of a subset of activated signaling molecules.

Rationale Mechanisms of angiogenesis in skeletal muscle remain poorly understood. Efforts to induce physiological angiogenesis hold promise for the treatment of diabetic microvascular disease and Peripheral Artery Disease (PAD), but are hindered by the complexity of physiological angiogenesis and by the poor angiogenic response of aged and diabetic patients. To date, the best therapy for diabetic vascular disease remains exercise, often a challenging option for patients with leg pain. PGC-1α, a powerful regulator of metabolism, mediates exercise-induced angiogenesis in skeletal muscle. Objective To test if, and how, PGC-1α can induce functional angiogenesis in adult skeletal muscle. Methods and Results We show here that muscle PGC-1α robustly induces functional angiogenesis in adult, aged, and diabetic mice. The process involves the orchestration of numerous cell types, and leads to patent, non-leaky, properly organized, and functional nascent vessels. These findings contrast sharply with the disorganized vasculature elicited by induction of VEGF alone. Bioinformatic analyses revealed that PGC-1α induces the secretion of secreted phosphoprotein 1 (SPP1), and the recruitment of macrophages. SPP1 stimulates macrophages to secrete monocyte chemoattractant protein-1 (MCP-1), which then activates adjacent endothelial cells, pericytes, and smooth muscle cells. In contrast, induction of PGC-1α in SPP1 −/− mice leads to immature capillarization and blunted arteriolarization. Finally, adenoviral delivery of PGC-1α into skeletal muscle of either young or old and diabetic mice improved the recovery of blood flow in the murine hind-limb ischemia model of PAD. Conclusions PGC-1α drives functional angiogenesis in skeletal muscle and likely recapitulates the complex physiological angiogenesis elicited by exercise.