Bcr: a negative regulator of the Bcr-Abl oncoprotein in leukemia.
The fusion of 5' parts of the BCR gene to the ABL gene at the second exon yields several forms of an oncogenic Bcr-Abl oncoprotein observed in several types of Philadelphia chromosome positive leukemia patients. The first exon of the BCR gene is a critical part of this fusion, as the coiled-coil domain at the amino terminal domain of the Bcr protein causes oligomerization of the Bcr-Abl oncoprotein forming tetramers, thereby activating the tyrosine kinase activity of the normally silent c-Abl protein. Another consequence of this Bcr-Abl fusion is the extensive autophosphorylation of the cis Bcr protein sequences on tyrosine residues. This review will summarize the effects of Bcr-Abl autophosphorylation on tyrosines as they relate to the oncogenic activity of Bcr-Abl, and as a means to inactivate the serine/threonine kinase activity of the Bcr protein. The review also discusses our findings that show that phosphoserine Bcr by means of a unique structure, binds to the Abl SH2 domain of the Bcr-Abl oncoprotein, and as a result this SH2 binding inhibits the oncogenic effects of the oncoprotein. Our results indicate that one effect of this binding is inhibition of the Bcr-Abl tyrosine kinase. Serine 354 of Bcr plays a major role in this inhibition. In the case of Bcr(64-413), serine 354 is required for the formation of the unique Bcr structure that binds to the Abl SH2 domain.
Arlinghaus
Ralph B
RB
Department of Molecular Pathology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, TX 77030, USA. rarlingh@mdanderson.org
D000595:Amino Acid Sequence; D000818:Animals; D016044:Fusion Proteins, bcr-abl; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D015513:Oncogene Proteins / Q000502:physiology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051562:Proto-Oncogene Proteins c-bcr; D014443:Tyrosine / Q000378:metabolism
D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl; C496613:BCR protein, human; C496614:Bcr protein, mouse; D051562:Proto-Oncogene Proteins c-bcr