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). Downregulates cytokine signaling by inhibiting the JAK/STAT signaling pathway. Acts by binding to JAK proteins and to IFNGR1 and inhibiting their kinase activity. In vitro, suppresses Tec protein-tyrosine activity. 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. Protein modification; protein ubiquitination. Interacts with multiple activated proteins of the tyrosine kinase signaling pathway including JAK family kinases, TEC, KIT, GRB2 and VAV (By similarity). Binding to JAKs is mediated through the KIR and SH2 domain to a phosphorylated tyrosine residue within the JAK JH1 domain (By similarity). Binds the SH3 domain of GRB2 via diproline determinants in the N-terminus, and the N-terminal regulatory domain of VAV (By similarity). 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 (By similarity). Interacts with CUL2. Interacts with AXL and FGFR3 (By similarity). Interacts with IGF1R (By similarity). Interacts with INSR (By similarity). Interacts with DCUN1D1 (By similarity). Detected in perinuclear cytoplasmic vesicles upon interaction with FGFR3. 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 (By similarity). Belongs to the SOCS1 family.