The function of ENSG00000114423 (CBLB, Cbl proto-oncogene B) is as follows. 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 (PubMed:20525694, PubMed:40101708). Negatively regulates TCR (T-cell receptor), BCR (B-cell receptor) and FCER1 (high affinity immunoglobulin epsilon receptor) signal transduction pathways (PubMed:40101708). In naive T-cells, inhibits VAV1 activation upon TCR engagement and imposes a requirement for CD28 costimulation for proliferation and IL-2 production (By similarity). Also acts by promoting PIK3R1/p85 ubiquitination, which impairs its recruitment to the TCR and subsequent activation (PubMed:11087752, PubMed:11526404). In activated T-cells, inhibits PLCG1 activation and calcium mobilization upon restimulation and promotes anergy (By similarity). Involved in LAG3-mediated inhibition of TCR signaling: following ligand-binding to LAG3, catalyzes 'Lys-63'-linked ubiquitination of LAG3, unleashing the LAG3 C-terminus from the membrane, and initiating a signaling that prevents TCR activation (PubMed:39030301, PubMed:40101708). In B-cells, acts by ubiquitinating SYK and promoting its proteasomal degradation (By similarity). Slightly promotes SRC ubiquitination (PubMed:14661060). May be involved in EGFR ubiquitination and internalization (PubMed:10086340). 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). {ECO:0000250|UniProtKB:Q3TTA7, ECO:0000269|PubMed:10022120, ECO:0000269|PubMed:10086340, ECO:0000269|PubMed:11087752, ECO:0000269|PubMed:11526404, ECO:0000269|PubMed:14661060, ECO:0000269|PubMed:20525694, ECO:0000269|PubMed:39030301, ECO:0000269|PubMed:40101708}.