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''Cbl'' (named after Casitas B-lineage Lymphoma) is a mammalian gene encoding the protein CBL which is an E3 ubiquitin-protein ligase involved in
cell signalling In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property of all cellula ...
and protein
ubiquitination Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. F ...
. Mutations to this gene have been implicated in a number of human cancers, particularly
acute myeloid leukaemia Acute myeloid leukemia (AML) is a cancer of the myeloid line of blood cells, characterized by the rapid growth of abnormal cells that build up in the bone marrow and blood and interfere with normal blood cell production. Symptoms may include ...
.


Discovery

In 1989 a virally encoded portion of the chromosomal mouse ''Cbl'' gene was the first member of the Cbl family to be discovered 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'', 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 A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to the tyrosine residues of specific proteins inside a cell. It functions as an "on" or "off" switch in many cellular functions. Tyrosine kinases belong to a larger cl ...
binding
domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined ** Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function *Do ...
'', and that this was the
oncogenic Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abno ...
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.


Structure

Full length ''c-Cbl'' has been found to consist of several regions encoding for functionally distinct protein domains: *
N-terminal The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amin ...
tyrosine kinase binding domain (TKB domain): determines the protein which it can bind to *
RING finger domain In molecular biology, a RING (short for Really Interesting New Gene) finger domain is a protein structural domain of zinc finger type which contains a C3HC4 amino acid motif which binds two zinc cations (seven cysteines and one histidine arrange ...
motif Motif may refer to: General concepts * Motif (chess composition), an element of a move in the consideration of its purpose * Motif (folkloristics), a recurring element that creates recognizable patterns in folklore and folk-art traditions * Moti ...
: recruits enzymes involved in ubiquitination * Proline-rich region: the site of interaction between Cbl and cytosolic proteins involved in Cbl's adaptor functions *
C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...
ubiquitin-associated domain (UBA domain): the site of ubiquitin binding This domain structure and the
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...
and
serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − for ...
-rich content of the protein product is typical of an "adaptor molecule" used in cell signalling pathways.


Homologues

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: # c-Cbl: ubiquitously expressed, 906 and 913 amino acids in length in humans and mice respectively # Cbl-b: ubiquitously expressed, 982 amino acids long. # Cbl-c: lacks the UBA domain and is therefore only 474 amino acids in length. It is primarily expressed in
epithelial cell Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercell ...
s however its function is poorly understood. Both c-Cbl and Cbl-b have
orthologues Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a sp ...
in '' D. melanogaster'' (D-Cbl) and ''
C. elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' ( ...
'' (Sli-1), hinting at a long evolutionary path for these proteins.


Function


Ubiquitin ligase

Ubiquitination is the process of chemically attaching
ubiquitin Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. F ...
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
ligase In biochemistry, a ligase is an enzyme that can catalyze the joining ( ligation) of two large molecules by forming a new chemical bond. This is typically via hydrolysis of a small pendant chemical group on one of the larger molecules or the enz ...
s. 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 Receptor tyrosine kinases (RTKs) are the high- affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine ...
. 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 A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane ...
for degradation.


Interactions

Cbl gene has been shown to interact with: *
Abl gene Tyrosine-protein kinase ABL1 also known as ABL1 is a protein that, in humans, is encoded by the ''ABL1'' gene (previous symbol ''ABL'') located on chromosome 9. c-Abl is sometimes used to refer to the version of the gene found within the mammalia ...
, * ARHGEF7, *
C-Met c-Met, also called tyrosine-protein kinase Met or hepatocyte growth factor receptor (HGFR), is a protein that in humans is encoded by the ''MET'' gene. The protein possesses tyrosine kinase activity. The primary single chain precursor protein is ...
, * CD2AP, * CSF1R. *
CRK Adapter molecule crk also known as proto-oncogene c-Crk is a protein that in humans is encoded by the ''CRK'' gene. The CRK protein participates in the Reelin signaling cascade downstream of DAB1. Function Adapter molecule crk is a member of ...
, *
CRKL Crk-like protein is a protein that in humans is encoded by the CRKL gene. Function v-CRK avian sarcoma virus CT10-homolog-like contains one SH2 domain and two SH3 domains. CRKL has been shown to activate the RAS and JUN kinase signaling path ...
, * EGFR,< *
FRS2 Fibroblast growth factor receptor substrate 2 is a protein that in humans is encoded by the ''FRS2'' gene. FRS2 is an 80 kDa membrane-anchored signal transducing adaptor protein (STAP) that links specific activated Receptor Tyrosine Kinases (RTKs) ...
, * FYN, * Grb2, * HCK, *
IGF1R The insulin-like growth factor 1 (IGF-1) receptor is a protein found on the surface of human cells. It is a transmembrane receptor that is activated by a hormone called insulin-like growth factor 1 (IGF-1) and by a related hormone called IGF-2 ...
, * LCP2;, *
NCK1 Cytoplasmic protein NCK1 is a protein that in humans is encoded by the ''NCK1'' gene. Gene The Nck (non-catalytic region of tyrosine kinase adaptor protein 1) belongs to the adaptor family of proteins. The nck gene was initially isolated from ...
, *
PDGFRA PDGFRA, i.e. platelet-derived growth factor receptor A, also termed PDGFRα, i.e. platelet-derived growth factor receptor α, or CD140a i.e. Cluster of Differentiation 140a, is a receptor located on the surface of a wide range of cell types. This r ...
, *
PIK3R1 Phosphatidylinositol 3-kinase regulatory subunit alpha is an enzyme that in humans is encoded by the ''PIK3R1'' gene. Function Phosphatidylinositol 3-kinase phosphorylates the inositol ring of phosphatidylinositol at the 3-prime position. Th ...
, *
PIK3R2 Phosphatidylinositol 3-kinase regulatory subunit beta is an enzyme that in humans is encoded by the ''PIK3R2'' gene. A recent study on gene expression indicated that the PIK3R2 gene might have a key role in pan-cancer prognosis. Interactions ...
, *
PLCG1 Phospholipase C, gamma 1, also known as PLCG1,is a protein that in humans involved in cell growth, migration, apoptosis, and proliferation. It is encoded by the ''PLCG1'' gene and is part of the PLC superfamily. Function PLCγ1 is a cell gro ...
, * PTK2B, *
PTPN11 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 huma ...
, * SH2B2, * SH3KBP1 *
SHC1 SHC-transforming protein 1 is a protein that in humans is encoded by the ''SHC1'' gene. SHC has been found to be important in the regulation of apoptosis and drug resistance in mammalian cells. SCOP classifies the 3D structure as belonging to t ...
, * SLA2, *
SORBS1 CAP/Ponsin protein, also known as Sorbin and SH3 domain-containing protein 1 is a protein that in humans is encoded by the ''SORBS1'' gene. It is part of a small family of adaptor proteins that regulate cell adhesion, growth factor signaling and c ...
, * SORBS2, *
SPRY2 Sprouty homolog 2 (Drosophila), also known as SPRY2, is a protein which in humans is encoded by the ''SPRY2'' gene. Function This gene encodes a protein belonging to the sprouty family. The encoded protein contains a carboxyl-terminal cysteine- ...
, * Syk, * UBE2L3, * VAV1, * YWHAB, * YWHAQ, and * ZAP-70,


References


Further reading

* * *


External links


Quips article describing CBL function
a
PDBe

OMIM entries on NOONAN SYNDROME-LIKE DISORDER WITH OR WITHOUT JUVENILE MYELOMONOCYTIC LEUKEMIA and CBL
* {{DEFAULTSORT:Cbl (Gene) Proteins