Aberrant overexpression of an epithelial marker, 14-3-3sigma, in a subset of hematological malignancies.
BACKGROUND
14-3-3sigma is a p53-mediated cell-cycle inhibitor in epithelial cells. The expression of 14-3-3sigma is frequently altered in cancers of epithelial origin associated with altered DNA methylation. Since its involvement in a non-epithelial tumor is unknown, we examined 14-3-3sigma expression in patients with haematological malignancies.


METHODS
We analyzed 41 hematopoietic cell lines and 129 patients with a variety of hematological malignancies for 14-3-3sigma expression with real-time RT-PCR. We also examined protein levels by Western blot analysis and DNA methylation status of the 14-3-3sigma gene by methylation-specific PCR analysis of bisulfite-treated DNA. In addition, mutations of p53 gene were identified by RT-PCR-SSCP analysis and the expression levels of 14-3-3sigma were compared with those of other cell-cycle inhibitor genes, CDKN2A and ARF.


RESULTS
The expression levels of 14-3-3sigma mRNA in almost all cell lines were low and comparable to those in normal hematopoietic cells except for 2 B-cell lines. On the contrary, 14-3-3sigma mRNA was aberrantly overexpressed frequently in mature lymphoid malignancies (30 of 93, 32.3%) and rarely in acute leukemia (3 of 35, 8.6%). 14-3-3sigma protein was readily detectable and roughly reflected the mRNA level. In contrast to epithelial tumors, methylation status of the 14-3-3sigma gene was not associated with expression in hematological malignancies. Mutations of p53 were identified in 12 patients and associated with lower expression of 14-3-3sigma. The expression levels of 14-3-3sigma, CDKN2A and ARF were not correlated with but rather reciprocal to one another, suggesting that simultaneous overexpression of any two of them is incompatible with tumor growth.


CONCLUSIONS
14-3-3sigma, an epithelial cell marker, was overexpressed significantly in a subset of mature lymphoid malignancies. This is the first report of aberrant 14-3-3sigma expression in non-epithelial tumors in vivo. Since the significance of 14-3-3sigma overexpression is unknown even in epithelial tumors such as pancreatic cancers, further analysis of regulation and function of the 14-3-3sigma gene in non-epithelial as well as epithelial tumors is warranted.
Motokura
Toru
T
Department of Hematology and Oncology, Faculty of Medicine, The University of Tokyo, Tokyo, Japan. motokura@grape.med.tottori-u.ac.jp
Nakamura
Yukari
Y
Sato
Hiroyuki
H
D048948:14-3-3 Proteins; D020727:ADP-Ribosylation Factors / Q000235:genetics; D001483:Base Sequence; D014408:Biomarkers, Tumor / Q000096:biosynthesis* / Q000235:genetics; D015153:Blotting, Western; D002453:Cell Cycle; D019175:DNA Methylation; D005092:Exonucleases / Q000096:biosynthesis* / Q000235:genetics; D005095:Exoribonucleases; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D019942:Genes, p16; D019337:Hematologic Neoplasms / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D018807:Polymorphism, Single-Stranded Conformational / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D015854:Up-Regulation
D048948:14-3-3 Proteins; D014408:Biomarkers, Tumor; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D005092:Exonucleases; D005095:Exoribonucleases; C413442:SFN protein, human; D020727:ADP-Ribosylation Factors