4.5 Article

Wnt pathway inhibitors are strongly down-regulated in pituitary tumors

Journal

ENDOCRINOLOGY
Volume 149, Issue 3, Pages 1235-1242

Publisher

ENDOCRINE SOC
DOI: 10.1210/en.2007-0542

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The etiology of sporadic pituitary tumors is currently unknown. The Writ 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 Writ 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 Writ 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 Writ 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 P-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 Writ pathways are important in pituitary tumorigenesis.

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