Essential negative regulator of type I and type II interferon (IFN) signaling, as well as that of other cytokines, including IL2, IL4, IL6 and leukemia inhibitory factor (LIF) (PubMed:9202125, PubMed:10064597, PubMed:15169905, PubMed:15522878). Downregulates cytokine signaling by inhibiting the JAK/STAT signaling pathway. Acts by binding to JAK proteins and to IFNGR1 and inhibiting their kinase activity (PubMed:9202125, PubMed:10064597, PubMed:15522878). In vitro, suppresses Tec protein-tyrosine activity (By similarity). Regulates IFN-gamma (IFNG)-mediated sensory neuron survival. Probable substrate recognition component of an ECS (Elongin BC-CUL2/5-SOCS-box protein) E3 ubiquitin ligase complex which mediates the ubiquitination and subsequent proteasomal degradation of target proteins (By similarity). Protein modification; protein ubiquitination. Interacts with multiple activated proteins of the tyrosine kinase signaling pathway including JAK family kinases, TEC, KIT, GRB2 and VAV. Binding to JAKs is mediated through the KIR and SH2 domain to a phosphorylated tyrosine residue within the JAK JH1 domain. Binds the SH3 domain of GRB2 via diproline determinants in the N-terminus, and the N-terminal regulatory domain of VAV. Interacts with the Elongin BC complex (ELOB and ELOC). Component of an ECS CBC(SOCS1) E3 ubiquitin-protein ligase complex which contains Elongin BC, CUL5, RBX1 and SOCS1. Interacts (via SH2 domain and SOCS box) with TRIM8. Interacts with CUL2. Interacts with AXL and FGFR3 (By similarity). Interacts with INSR. Interacts with TRIM8 (By similarity). Interacts with DCUN1D1 (By similarity). Interacts with IFNGR1 (PubMed:15522878). Detected in perinuclear cytoplasmic vesicles upon interaction with FGFR3. High expression in thymus. Lower expression in lung and spleen (PubMed:9202125). Expressed in both Th1 and Th2 cells. In the developing brain, expressed at low levels from 10 dpc stages to young adulthood (P25) with peak levels from 14 dpc to P8. In the cortex, expression first observed at 14 dpc uniformly in all cells. Also expressed in the innermost layers of the developing retina. Levels of expression remain unchanged from P8 until adulthood. In the peripheral nervous system, high levels found in virtually all neurons of the dorsal root ganglion. By a subset of cytokines including those belonging to the interferon, interleukin and colony-stimulating factor families. The ESS and SH2 domains are required for JAK phosphotyrosine binding. Further interaction with the KIR domain is necessary for signal and kinase inhibition. The SOCS box domain mediates the interaction with the Elongin BC complex, an adapter module in different E3 ubiquitin ligase complexes. The Elongin BC complex binding domain is also known as BC-box with the consensus [APST]-L-x(3)-C-x(3)-[AILV] and is part of the SOCS box. Mice exhibit lymphocyte deficiency and degeneration of the liver parenchyma. Animals die within 3 weeks of age. Mutants show a much higher frequency of CD8 single positive thymocytes (PubMed:24880459). Belongs to the SOCS1 family.