CIS1, a cytokine-inducible SH2 protein, suppresses BCR/ABL-mediated transformation. Involvement of the ubiquitin proteasome pathway.
OBJECTIVE
BCR/ABL is a chimeric oncoprotein that exhibits deregulated tyrosine kinase activity and is implicated in the pathogenesis of Philadelphia chromosome (Ph)-positive leukemia. A general understanding of BCR/ABL signaling events is emerging, but little is known about the endogenous inhibitors of p210 BCR/ABL. The present study focused attention on CIS1, a cytokine-inducible SH2 protein, as a potential physiologic antagonist for BCR/ABL.


METHODS
The murine hematopoietic cell line NSF/N1.H7 stably transfected with BCR/ABL was compared to the parental counterparts for induction of CIS1 by immunoblotting and immunoprecipitation. Cells were treated with a proteasome inhibitor to examine the effect of a proteasome inhibitor on CIS1 protein expression. To determine the effect of CIS1 on BCR/ABL-mediated transformation, we generated Rat-1 fibroblasts transfected with either a control vector, CIS1, BCR/ABL p210, or CIS1 plus BCR/ABL p210.


RESULTS
Three forms of CIS1 with molecular masses of 32, 37, and 47 kDa were detected in BCR/ABL-transformed cells. The 47-kDa protein was a ubiquitinated protein. The proteasome inhibitor increased the formation of complexes between CIS1 and BCR/ABL. Transformation of p210 BCR/ABL was significantly suppressed in cells overexpressing CIS1.


CONCLUSIONS
The results suggest that CIS1 is an endogenous inhibitor of p210 BCR/ABL and is likely to be important in the pathogenesis of Ph-positive leukemia.
First Department of Internal Medicine, Tokyo Medical University, Tokyo, Japan. tauchi@tokyo-med.ac.jp
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Tauchi
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Yoshimura
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Ohyashiki
D016475:3T3 Cells / Q000473:pathology; D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D003546:Cysteine Endopeptidases / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005347:Fibroblasts / Q000473:pathology; D016044:Fusion Proteins, bcr-abl / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology*; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000378:metabolism*; D051379:Mice; D008894:Milk Proteins; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000502:physiology; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D014452:Ubiquitins / Q000378:metabolism*; D018909:src Homology Domains
D003546:Cysteine Endopeptidases; D004268:DNA-Binding Proteins; D016044:Fusion Proteins, bcr-abl; D017874:Immediate-Early Proteins; D008894:Milk Proteins; D009097:Multienzyme Complexes; D046988:Proteasome Endopeptidase Complex; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D050799:STAT5 Transcription Factor; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014452:Ubiquitins