Cbl (named after Casitas B-lineage Lymphoma) is a mammalian gene family. CBL gene, a part of the Cbl family, encodes the protein CBL which is an E3 ubiquitin-protein ligase involved in cell signalling and protein ubiquitination. Mutations to this gene have been implicated in a number of human cancers, particularly acute myeloid leukaemia. [5]
In 1989 a virally encoded portion of the chromosomal mouse Cbl gene was the first member of the Cbl family to be discovered [6] and was named v-Cbl to distinguish it from normal mouse c-Cbl. The virus used in the experiment was a mouse-tropic strain of Murine leukemia virus isolated from the brain of a mouse captured at Lake Casitas, California known as Cas-Br-M, [7] and was found to have excised approximately a third of the original c-Cbl gene from a mouse into which it was injected. Sequencing revealed that the portion carried by the retrovirus encoded a tyrosine kinase binding domain , and that this was the oncogenic form as retroviruses carrying full-length c-Cbl did not induce tumor formation. The resultant transformed retrovirus was found to consistently induce a type of pre-B lymphoma, known as Casitas B-lineage lymphoma, in infected mice.
Full length c-Cbl has been found to consist of several regions encoding for functionally distinct protein domains:
This domain structure and the tyrosine and serine-rich content of the protein product is typical of an "adaptor molecule" used in cell signalling pathways. [8]
Three mammalian homologues have been characterized, which all differ in their ability to function as adaptor proteins due to the differing lengths of their C-terminal UBA domains:
Both c-Cbl and Cbl-b have orthologues in D. melanogaster (D-Cbl) and C. elegans (Sli-1), hinting at a long evolutionary path for these proteins. [8]
Ubiquitination is the process of chemically attaching ubiquitin monomers to a protein, thereby targeting it for degradation. As this is a multi-step process, several different enzymes are involved, the final one being a member of the E3 family of ligases. Cbl functions as an E3 ligase, and therefore is able to catalyse the formation of a covalent bond between ubiquitin and Cbl's protein substrate - typically a receptor tyrosine kinase. The RING-finger domain mediates this transfer, however like other E3 ligases of the RING type no intermediate covalent bond is formed between ubiquitin and the RING-finger domain. The stepwise attachment of ubiquitin to the substrate receptor tyrosine kinase can lead to its removal from the plasma membrane and subsequent trafficking to the lysosome for degradation.
Cbl gene has been shown to interact with:
Tyrosine-protein kinase ABL1 also known as ABL1 is a protein that, in humans, is encoded by the ABL1 gene located on chromosome 9. c-Abl is sometimes used to refer to the version of the gene found within the mammalian genome, while v-Abl refers to the viral gene, which was initially isolated from the Abelson murine leukemia virus.
Growth factor receptor-bound protein 2, also known as Grb2, is an adaptor protein involved in signal transduction/cell communication. In humans, the GRB2 protein is encoded by the GRB2 gene.
Tyrosine-protein phosphatase non-receptor type 11 (PTPN11) also known as protein-tyrosine phosphatase 1D (PTP-1D), Src homology region 2 domain-containing phosphatase-2 (SHP-2), or protein-tyrosine phosphatase 2C (PTP-2C) is an enzyme that in humans is encoded by the PTPN11 gene. PTPN11 is a protein tyrosine phosphatase (PTP) Shp2.
Adapter molecule crk also known as proto-oncogene c-Crk is a protein that in humans is encoded by the CRK gene.
Growth factor receptor-bound protein 10 also known as insulin receptor-binding protein Grb-IR is a protein that in humans is encoded by the GRB10 gene.
Proto-oncogene tyrosine-protein kinase Fyn is an enzyme that in humans is encoded by the FYN gene.
Phosphatidylinositol 3-kinase regulatory subunit alpha is an enzyme that in humans is encoded by the PIK3R1 gene.
Tyrosine-protein phosphatase non-receptor type 6, also known as Src homology region 2 domain-containing phosphatase-1 (SHP-1), is an enzyme that in humans is encoded by the PTPN6 gene.
RAS p21 protein activator 1 or RasGAP, also known as RASA1, is a 120-kDa cytosolic human protein that provides two principal activities:
GRB2-associated-binding protein 1 is a protein that in humans is encoded by the GAB1 gene.
Protein tyrosine kinase 2 beta is an enzyme that in humans is encoded by the PTK2B gene.
CBL-B is an E3 ubiquitin-protein ligase that in humans is encoded by the CBLB gene. CBLB is a member of the CBL gene family.
Fibroblast growth factor receptor substrate 2 is a protein that in humans is encoded by the FRS2 gene.
Proto-oncogene vav is a protein that in humans is encoded by the VAV1 gene.
Cytoplasmic protein NCK1 is a protein that in humans is encoded by the NCK1 gene.
Tyrosine-protein phosphatase non-receptor type 12 is an enzyme that in humans is encoded by the PTPN12 gene.
BAG family molecular chaperone regulator 3 is a protein that in humans is encoded by the BAG3 gene. BAG3 is involved in chaperone-assisted selective autophagy.
SH2B adapter protein 2 is a protein that in humans is encoded by the SH2B2 gene.
Tyrosine-protein kinase BLK, also known as B lymphocyte kinase, is a non-receptor tyrosine kinase that in humans is encoded by the BLK gene. It is of the Src family of tyrosine kinases.
Signal transduction protein CBL-C is a protein that in humans is encoded by the CBLC gene.