Background: Epigenetic silencing of tumor suppressor genes (TSG) is involved in development and
progression of cancers. Re-expression of TSG is inversely proportionate with STAT3 signaling pathways.
Demethylation of DNA by 5-Azacytidine (5-Aza) results in re-expression of silenced TSG. Forced expression of
PRG2 by 5-Aza induced apoptosis in cancer cells. Imatinib is a tyrosine kinase inhibitor that potently inhibits BCR/
ABL tyrosine kinase resulting in hematological remission in CML patients. However, majority of CML patients treated
with imatinib would develop resistance under prolonged therapy. Methods: CML cells resistant to imatinib were
treated with 5-Aza and cytotoxicity of imatinib and apoptosis were determined by MTS and annexin-V, respectively.
Gene expression analysis was detected by real time-PCR, STATs activity examined using Western blot and methylation
status of PRG2 was determined by pyrosequencing analysis. Result: Expression of PRG2 was significantly higher in
K562-R+5-Aza cells compared to K562 and K562-R (p=0.001). Methylation of PRG2 gene was significantly decreased
in K562-R+5-Aza cells compared to other cells (p=0.021). STAT3 was inactivated in K562-R+5-Aza cells which showed
higher sensitivity to imatinib. Conclusion: PRG2 gene is a TSG and its overexpression might induce sensitivity to
imatinib. However, further studies are required to evaluate the negative regulations of PRG2 on STAT3 signaling.
* Title and MeSH Headings from MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.