Translocation Fusion proteins

Inhibition of hematopoietic growth factors Imatinib (Glivec ) is applied to treat chronic myeloid leukemia in Philadelphia-chromosome positive patients. In these patients, translocation of parts of chromosomes 9 and 22 results in the expression of a fusion protein with increased tyrosine kinase activity, called Bcr-Abl. Imatinib is a small Mw inhibitor selective for the tyrosine kinase activity of Bcr-Abl. Thereby, it inhibits the Bcr-Abl induced cell cycle progression and the uncontrolled proliferation of tumor cells. 

A well-known use of molecular methods is in the study of chromosomal translocations. Thus, in Philadelphia chromosome (ph1) positive chronic myelogenous leukemia (CML), the C-abl oncogene on chromosome 9 is translocated to a region on chromosome 22 called the breakpoint cluster region, or bcr. This (t9 22) translocation results in production of an abnormal fusion protein... 

Figure 2. Genetic aberrations observed in HAT genes, (a) Schematic representation of a balanced chromosomal translocation. These translocations result in the formation two new fusion genes, which can give rise to one or two fusion proteins, (b) Examples of nonsense (RTS patient RT163.1), missense (RT209.1), deletion (followed by frame shift RT231.1) mutations, as well as sphee site acceptor (RT211.3) or splice site donor (RT39.1) mutations...

Figure 4. Leukaemic gene fusions involving HATs. (a) The t(8 16) translocation result in the MOZ-CBP fusion protein, while inv(8) gives rise to MOZ-T1F2. (b) Hypothetical model to explain how MOZ-T1F2 and MOZ-CBP fusions result in a similar leukaemia cell phenotype. See text for details, (c) The t(ll 16) and t(l 1 22) result in the MLL-CBP and MLL-p300 gene fusions, respectively...

Figure 2. Chromosomal translocations leading the production of a MYST HAT fusion protein and cancer, (a) structure of different MYST HAT fusion proteins leading to cancer. Numbers indicate amino acid positions at break points, (b) Model for die consequences of EPCl-PCL fusion on chromatin function...

Kitabayashi 1, Aikawa Y, Nguyen LA, Yokoyama A, Ohki M (2001a) Activation of AMLl-mediated transcription by MOZ and inhibition by the MOZ-CBP fusion protein. Embo J 20 7184-7196 Kitabayashi 1, Aikawa Y, Yokoyama A, Hosoda F, Nagai M, Kakazu N, Abe T, Ohki M (2001b) Fusion of MOZ and p300 histone acetyltransferases in acute monocytic leukemia with a t(8 22)(pll ql3) chromosome translocation. Leukemia 15 89-94... 

Like many other nonreceptor tyrosine kinases, Abl tyrosine kinase may be converted by mutations into a dominant oncoprotein and thus contribute to tumor formation. Abl tyrosine kinase was first discovered as the oncogene of murine Abelson leukemia virus. Chronic myelogenic leukemia in humans is cause by a chromosome translocation in which a fusion protein is created of Abl tyrosine kinase and a Bcr protein (c Chapter 14). The result is a greatly increased tyrosine kinase activity, to which a causal role in occurrence of this leukemia is attributed. 

Fig. 14.4. Formation of a hybrid oncoprotein, illustrated by translocation of the Abl tyrosine kinase. The gene for the Ser-spedfic protein kinase BCR is fused with a part of the c-abl gene in the process of the Philadelphia chromosome translocation. Fusion genes are produced on chromosome 22, coding for various fusion proteins. The most important fusion proteins are the p -and p -BCR-Abl hybrid proteins, which have increased Tyr kinase activity and an altered subcel-lular location.

A. General description Denileukin dif-titox is a recombinant, DNA-derived, interleukin-2 receptor specific ligand, cytotoxic fusion protein consisting of diphtheria toxin fragments A and B fused to interleukin-2. It is produced by expression of a recombinant fusion protein in Escherichia coli that contains nucleotide sequences for human interleukin-2, and sequences for the enzymatically active fragment A of diphtheria toxin and the membrane-translocating portion of diph-... 

Up-regulation of annexin 2 has also been implicated in pro-B cell acute lymphoblastic leukaemia ALL (Matsunaga et al., 2004). This occurs as a result of a different translocation t(17 19)(q22 pl3) and the expression of the fusion protein E2A-HLF is also associated with poor prognosis, hypercalcemia and haemorrhagic complications. Expression of E2A-HLF was sufficient to induce annexin 2 overexpression in leukaemic cell lines. 

Imatinib (STI571) is an inhibitor of the tyrosine kinase domain of the Bcr-Abl oncoprotein and prevents the phosphorylation of the kinase substrate by ATP. It is indicated for the treatment of chronic myelogenous leukemia (CML), a pluripotent hematopoietic stem cell disorder characterized by the t(9 22) Philadelphia chromosomal translocation. This translocation results in the Bcr-Abl fusion protein, the causative agent in CML, and is present in up to 95% of patients with this disease. This agent inhibits other activated receptor tyrosine kinases for platelet-derived growth factor receptor (PDGFR), stem cell factor (SCF), and c-kit. 

If the interaction occurs, emitted light intensity will decrease at 476 nm and increase at 527 nm on addition of epinephrine to cells expressing the fusion proteins. If the interaction does not occur, the wavelength of the emitted light will remain at 476 nm. There are several reasons why this might fail for example, the fusion proteins (1) are inactive or otherwise unable to interact, (2) are not translocated to their normal subcellular location, or (3) are not stable to proteolytic breakdown. 

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