PTPROt inactivates the oncogenic fusion protein BCR/ABL and suppresses transformation of K562 cells
Authors: Tasneem Motiwala
Kalpana Ghoshal
Jharna Datta
Satavisha Roy
David M Lucas
Samson T Jacob
Sarmila Majumder
Huban Kutay
Journal: Journal of Biological Chemistry (2009)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Chronic myelogenous leukemia; c-abl kinase; BCR; PTPROt; dephosphorylate
Affiliations: Department of Molecular and Cellular Biochemistry, the Division of Hematology-Oncology, Department of Internal Medicine, College of Medicine, and the Comprehensive Cancer Center, Ohio State University, Columbus, Ohio 43210., Department of Molecular and Cellular Biochemistry, the Division of Hematology-Oncology, Department of Internal Medicine, College of Medicine, and the Comprehensive Cancer Center, Ohio State University, Columbus, Ohio 43210; Department of Molecular and Cellular Biochemistry, the Division of Hematology-Oncology, Department of Internal Medicine, College of Medicine, and the Comprehensive Cancer Center, Ohio State University, Columbus, Ohio 43210. Electronic address: .

Abstract:  Chronic myelogenous leukemia is typified by constitutive activation of the c-abl kinase as a result of its fusion to the breakpoint cluster region (BCR). Because the truncated isoform of protein-tyrosine phosphatase receptor-type O (PTPROt) is specifically expressed in hematopoietic cells, we tested the possibility that it could potentially dephosphorylate and inactivate the fusion protein bcr/abl. Ectopic expression of PTPROt in the chronic myelogenous leukemia cell line K562 indeed resulted in hypophosphorylation of bcr/abl and reduced phosphorylation of its downstream targets CrkL and Stat5, confirming that PTPROt could inactivate the function of bcr/abl. Furthermore, the expression of catalytically active PTPROt in K562 cells caused reduced proliferation, delayed transition from G0/G1 to S phase, loss of anchorage independent growth, inhibition of ex vivo tumor growth, and increased their susceptibility to apoptosis, affirming that this tyrosine phosphatase can revert the transformation potential of bcr/abl. Additionally, the catalytically inactive PTPROt acted as a trapping mutant that was also able to inhibit anchorage independence and facilitate apoptosis of K562 cells. The inhibitory action of PTPROt on bcr/abl was also confirmed in a murine myeloid cell line overexpressing bcr/abl. PTPROt expression was suppressed in K562 cells and was relieved upon treatment of the cells with 5-azacytidine, an inhibitor of DNA methyltransferase, with concomitant hypomethylation of the PTPRO CpG island. These data demonstrate that suppression of PTPROt by promoter methylation could contribute to the augmented phosphorylation and constitutive activity of its substrate bcr/abl and provide a potentially significant molecular therapeutic target for bcr/abl-positive leukemia. 

Retracted: Yes

PubPeer comments:
 Figure 3. * Red boxes: The b-actin panel shown in Figure 3A looks similar the b-actin panel shown in Figure 3C.  , 
 Figure 5A. Two of the four flow cytometry panels appear to contain groups of dots that look very similar. Boxes of the same color draw attention to several of these areas.  This concern was reported to the journal in July 2014. The authors sent the  raw data files, which looked identical to the published images. The editor accepted that and did not take any action. , 
 March 2021 Retraction: https: journals.plos.org plosone article?id=10.1371 journal.pone.0248927 It reads:  Following the publication of this article [1], concerns were raised regarding the results presented in Fig 1, 3, and 5. Specifically, * In Fig 1, vertical irregularities have been detected on either side of lane 5 of the SUMO-p53 panel. The authors explained that the underlying blot was spliced to present pertinent results only and provided underlying data confirming the validity of the published panel. * The u03b2-actin blots of Figs 3A and 3C appear similar. The authors explained that the Fig 3A u03b2-actin blot was inadvertently duplicated, and that as a result the wrong panel was included for the Fig 3C u03b2-actin results. * In Fig 5A, repetitive clusters of signal have been detected in the FACS results for the HA-p53b and HA-p53b(K375R) panels. The authors provided additional individual level data for the published blots as well as results from triplicate experiments. Assessment of the data deriving from the triplicate experiment samples highlighted similar repetitive clusters of signal between the triplicate results, and the provided FACS results are more similar than would be expected from independent triplicate samples. In addition, the individual level data provided for the published FACS panels shows that for the none, HA, and HA-p53b panels the % Gated results of the upper left quadrants have been reported as the upper right quadrant results and vice versa. The corresponding author clarified that only the lower right quadrants were used to analyse apoptosis rates. The authors provided some underlying data to support the Figs 1 and 3 results, as well as raw FACS data supporting the results presented in the Fig 5 u201cnoneu201d panel, but the raw data files to support the Fig 5 HA, HA-p53b, and HA-p53b(K375R) results are no longer available. In light of the concerns affecting the Fig 5A results that question the integrity of the reported FACS data, the PLOS ONE Editors retract this article. LJH agreed with the retraction. XML, FFY, YFY and RZ either did not respond directly or could not be reached. ,