Wnt pathway inhibitors are strongly down-regulated in pituitary tumors.
The etiology of sporadic pituitary tumors is currently unknown. The Wnt pathways have been implicated in the pathogenesis of a variety of human tumors, but the role of these pathways in pituitary tumors is unclear. Microarray analysis using the Affymetrix HG U133 plus 2.0 GeneChips identified four secreted frizzled-related protein (sFRP) family members of Wnt pathway inhibitors that were differentially expressed in both nonfunctioning and clinically functioning pituitary tumors (n = 20) compared with normal pituitary controls (n = 3). Reduced tumor expression of Wnt inhibitory factor-1 (WIF1), sFRP2, and sFRP4 mRNA was confirmed by real-time quantitative RT-PCR (P <0.001 and P = 0.002 and 0.013, respectively) in all pituitary subtypes. Hypermethylation of the WIF1 promoter was present in 88% of the pituitary tumors (n = 41). Seventy-six percent of pituitary tumors demonstrated absent or weak cytoplasmic WIF1 staining by immunohistochemistry (n = 41), although preserved staining was seen in some functioning tumors, with strong staining in 92% of normal pituitary controls (n = 13). The Wnt pathway target gene cyclin D1 was found to be up-regulated specifically in the nonfunctioning pituitary tumors compared with controls at both mRNA and protein level, supportive of activation of the Wnt-beta-catenin pathway. Nuclear accumulation of beta-catenin, however, was not observed in any pituitary tumors (n = 70). By transfecting GH3 cells with WIF1, decreased cell proliferation and colony formation was observed compared with empty vector controls. In conclusion, our data suggest that WIF1 may be a tumor suppressor, specifically in nonfunctioning pituitary tumors, and that the Wnt pathways are important in pituitary tumorigenesis.
Elston
Marianne S
MS
Cancer Genetics Unit, Kolling Institute of Medical Research, Royal North Shore Hospital, St. Leonards, New South Wales 2065, Australia. marianne@med.usyd.edu.au
Gill
Anthony J
AJ
Conaglen
John V
JV
Clarkson
Adele
A
Shaw
Janet M
JM
Law
Andrew J J
AJ
Cook
Raymond J
RJ
Little
Nicholas S
NS
Clifton-Bligh
Roderick J
RJ
Robinson
Bruce G
BG
McDonald
Kerrie L
KL
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D016022:Case-Control Studies; D002460:Cell Line; D049109:Cell Proliferation; D019938:Cyclin D1 / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008875:Middle Aged; D010911:Pituitary Neoplasms / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism*; D052683:Somatotrophs / Q000378:metabolism; D014162:Transfection; D051176:beta Catenin / Q000378:metabolism; D000099274:Frizzled-Related Proteins; D000094742:Secreted Frizzled-Related Proteins
D048868:Adaptor Proteins, Signal Transducing; D019938:Cyclin D1; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D051176:beta Catenin; D000099274:Frizzled-Related Proteins; C109618:SFRP2 protein, human; D000094742:Secreted Frizzled-Related Proteins; C118723:SFRP4 protein, human; C485569:WIF1 protein, human; C521045:Wif1 protein, rat