The Endogenous Fibroblast Growth Factor-2 Antisense Gene Product Regulates Pituitary Cell Growth and Hormone Production

Abstract

Basic fibroblast growth factor (bFGF; FGF-2) is one of 19 related members of a growth factor family with mitogenic and hormone-regulatory functions. In Xenopus laevis oocytes, a 1.5-kb FGF-2 antisense (GFG) RNA complementary to the third exon and 3'-untranslated region (UTR) of FGF-2 mRNA has been implicated in FGF-2 mRNA editing and stability. The human homolog has been cloned, and we localized this gene by yeast artificial chromosome (YAC), somatic cell, and radiation hybrid panels to the same chromosomal site as FGF-2 (chromosome 4, JO4513 adjacent to D4S430), confirming this as a human endogenous antisense gene. The full-length GFG antisense RNA encodes a 35-kDa protein, which is highly homologous with the MutT family of antimutator nucleosidetriphosphatases (NTPases). We show that human pituitary tumors express FGF-2 and its endogenous antisense partner GFG. While normal pituitary expresses GFG but not FGF-2, pituitary adenomas express FGF-2 and have reduced levels of GFG; aggressive and recurrent adenomas expressed more FGF than GFG mRNA. To examine the effects of this antisense gene in the pituitary, we transfected the pituitary-derived GH4 mammosomatotroph cell line with constructs encoding the full-length human GFG cDNA. Transiently and stably transfected cells expressed the 35-kDa GFG protein that was localized to the cytoplasm. These cells exhibited enhanced PRL expression as documented by transiently transfected PRL-luciferase reporter assay and by endogenous PRL protein. GFG expression in these cells did not alter endogenous FGF-2 expression but increased the proportion of the higher molecular mass 22-kDa form of GH. Moreover, GFG expression inhibited cell proliferation as shown by [(3)H]thymidine incorporation, proliferating cell nuclear antigen (PCNA) nuclear staining, and cell cycle analysis. We conclude that the GFG-encoded protein has divergent hormone-regulatory and antiproliferative actions in the pituitary that are independent of FGF-2 expression. GFG represents a novel mechanism involved in restraining pituitary tumor cell growth while promoting hormonal activity.

Impaired FGF signaling contributes to cleft lip and palate

“…Although the literature described this gene as a potential antisense transcript, the UCSC genome browser and NCBI (NP-009014) both have predicted the protein sequence for the gene. Additionally, the NUDT6 protein (also referred to as GFG) has been identified in human pituitary tumors, possibly representing a novel mechanism for regulating tumor cell growth (31). The K172N mutation was found in an individual from Iowa with CLP; however, there was no family history of clefting and no familial DNA available.…”

Epigenetic Silencing through DNA and Histone Methylation of Fibroblast Growth Factor Receptor 2 in Neoplastic Pituitary Cells

“…15 We have previously demonstrated altered expression of several members of the FGFR family in pituitary tumors. 16 In particular, we found that FGFR4 is N-terminally truncated to yield a pituitary tumor-derived FGFR4 16,17 as a result of alternative transcription initiation using a cryptic promoter.…”

Fibroblast Growth Factor 2 and Estrogen Control the Balance of Histone 3 Modifications Targeting MAGE-A3 in Pituitary Neoplasia

“…Selected FGF ligands are overexpressed in pituitary tumors (13). Moreover, the human endogenous FGF antisense gene (GFG) is expressed in the normal pituitary where it restricts cell proliferation, and its expression is reduced in pituitary tumors (14).…”