Acquired uniparental disomy of chromosome 9p is a frequent stem cell defect in polycythemia vera.
OBJECTIVE
Clonal stem cell proliferation and increased erythrocyte mass are hallmarks of the myeloproliferative disorder polycythemia vera (PV). The molecular basis of PV is unknown.


METHODS
We carried out a genome-wide screening for loss of heterozygosity (LOH) and analyzed candidate genes within the LOH loci.


RESULTS
Three genomic regions were identified on chromosomes 9p, 10q, and 11q. The presence of these LOHs in both myeloid and lymphoid cells indicated their stem cell origin. The 9pLOH prevalence is approximately 33% and is the most frequent chromosomal lesion described in PV so far. We report that the 9pLOH is due to mitotic recombination and therefore remains undetectable by cytogenetic analysis. Nineteen candidate genes were selected within the 9pLOH region for sequencing and expression analysis. No mutations were found in these genes; however, unexpectedly, increased expression of the transcription factor NFI-B was detected in granulocytes and CD34(+) cells in PV with 9pLOH. Since a member of the NFI gene family (NFI-X) was reported to result in TGF-beta resistance when overexpressed in vitro (TGF-beta is a known inhibitor of hematopoiesis), we transfected the NFI-B gene to the mouse 32D cell line. We found that overexpression of the NFI-B gene confers TGF-beta resistance in vitro.


CONCLUSIONS
We characterized a new region on chromosome 9p frequently involved in LOH in PV. Analysis of genes within this 9pLOH region revealed increased expression of the NFI-B gene. Our in vitro studies suggest that TGF-beta resistance may be the physiologic mechanism of clonal stem cell expansion in PV.
Kralovics
Robert
R
Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA.
Guan
Yongli
Y
Prchal
Josef T
JT
D000818:Animals; D018952:Antigens, CD34 / Q000032:analysis; D002352:Carrier Proteins / Q000235:genetics; D002879:Chromosomes, Human, Pair 10; D002880:Chromosomes, Human, Pair 11; D002899:Chromosomes, Human, Pair 9; D004252:DNA Mutational Analysis; D004351:Drug Resistance / Q000235:genetics; D015870:Gene Expression; D019942:Genes, p16; D006412:Hematopoietic Stem Cells / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D019656:Loss of Heterozygosity; D008565:Membrane Proteins; D051379:Mice; D009154:Mutation; D051839:NFI Transcription Factors; D011087:Polycythemia Vera / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D024182:Uniparental Disomy
D018952:Antigens, CD34; D002352:Carrier Proteins; C111442:MPDZ protein, human; D008565:Membrane Proteins; C491750:Mpdz protein, mouse; D051839:NFI Transcription Factors; C484683:Nfib protein, mouse; D014157:Transcription Factors; D016212:Transforming Growth Factor beta