Methylation and silencing of protein tyrosine phosphatase receptor type O in chronic lymphocytic leukemia.
OBJECTIVE
Previous studies in our laboratory have shown the progressive methylation and suppression of the gene encoding protein tyrosine phosphatase, PTPRO, in the livers of rats fed a methyl-deficient diet that induces hepatocarcinogenesis. Subsequently, we observed the methylation of PTPRO in primary human lung tumors and also showed its potential tumor suppressor characteristics. The present study was undertaken to investigate whether the truncated form of PTPRO (PTPROt), specifically expressed in naïve B lymphocytes, was also methylated and suppressed in chronic lymphocytic leukemia (CLL), a disease generally affecting B lymphocytes.


RESULTS
Initial screening showed that 60% of the 52 CLL samples analyzed using methylation-specific PCR assay were methylated compared with B lymphocytes from normal individuals, which were not methylated. The expression of PTPROt, as measured by semiquantitative reverse transcription-PCR, inversely correlated with methylation in the few samples tested. Analysis of additional samples (n = 50) by combined bisulfite restriction analysis showed that the PTPRO CpG island was methylated in 82% of patients with CLL compared with B lymphocytes from normal individuals. Furthermore, overall expression of PTPRO was reduced in CLL relative to normal lymphocytes. The PTPRO gene was also suppressed by methylation in the CLL cell line WaC3CD5, where it could be reactivated upon treatment with the DNA hypomethylating agent 5-AzaC. Ectopic expression of PTPROt in a nonexpressing cell line increased growth inhibition with fludarabine treatment, a therapy commonly used for CLL.


CONCLUSIONS
This study reveals the potential role of PTPRO methylation and silencing in CLL tumorigenesis and also provides a novel molecular target in the epigenetic therapy.
Motiwala
Tasneem
T
Department of Molecular and Cellular Biochemistry, Ohio State University, Columbus, Ohio 43210, USA.
Majumder
Sarmila
S
Kutay
Huban
H
Smith
David Spencer
DS
Neuberg
Donna S
DS
Lucas
David M
DM
Byrd
John C
JC
Grever
Michael
M
Jacob
Samson T
ST
D001402:B-Lymphocytes / Q000378:metabolism; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics* / Q000628:therapy*; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D016133:Polymerase Chain Reaction; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism* / Q000502:physiology; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013447:Sulfites / Q000494:pharmacology; D014740:Vidarabine / Q000031:analogs & derivatives / Q000494:pharmacology
D008565:Membrane Proteins; D013447:Sulfites; C516888:PTPRO protein, human; D017027:Protein Tyrosine Phosphatases; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3; D014740:Vidarabine; C024352:fludarabine; C009279:sodium bisulfite