E3 ubiquitin-protein ligase which accepts ubiquitin from specific E2 ubiquitin-conjugating enzymes, and transfers it to substrates, generally promoting their degradation by the proteasome. Negatively regulates TCR (T-cell receptor, BCR (B-cell receptor and FCER1 (high affinity immunoglobulin epsilon receptor signal transduction pathways. In naive T-cells, inhibits VAV1 activation upon TCR engagement and imposes a requirement for CD28 costimulation for proliferation and IL-2 production. Also acts by promoting PIK3R1/p85 ubiquitination, which impairs its recruitment to the TCR and subsequent activation. In activated T-cells, inhibits PLCG1 activation and calcium mobilization upon restimulation and promotes anergy. In B-cells, acts by ubiquitinating SYK and promoting its proteasomal degradation. Slightly promotes SRC ubiquitination. May be involved in EGFR ubiquitination and internalization. May be functionally coupled with the E2 ubiquitin-protein ligase UB2D3. In association with CBL, required for proper feedback inhibition of ciliary platelet-derived growth factor receptor-alpha (PDGFRA signaling pathway via ubiquitination and internalization of PDGFRA (By similarity.,CBLB,Cbl-b,Nbla00127,RNF56,Cancer,Cell Biology & Developmental Biology,Ubiquitin,Ubiquitin-Proteasome Signaling Pathway,Endocrine & Metabolism,Insulin Receptor Signaling Pathway,Immunology & Inflammation,B Cell Receptor Signaling Pathway,Cell Intrinsic Innate Immunity Signaling Pathway,CBLB