<p>Cbl (Casitas B-lineage lymphoma) is an adaptor protein that functions as a negative regulator of many signalling pathways that start from receptors at the cell surface, including tyrosine kinases, cytokine receptors, and T-cell or B-cell receptors. There are three Cbl related proteins known to date: Cbl, CblB, and CblC/Cbl3 [<cite idref="PUB00055539"/>]. Cbls function as ubiquitin E3 ligase proteins, accepting ubiquitin from specific E2 ubiquitin-conjugating enzymes and transferring it to substrates, promoting their degradation [<cite idref="PUB00055540"/>] or endocytosis [<cite idref="PUB00055541"/>]. </p> Adaptor protein Cbl