Targeted expression of a human pituitary tumor–derived isoform of FGF receptor-4 recapitulates pituitary tumorigenesis
Shereen Ezzat, … , Gillian E. Wu, Sylvia L. Asa
Shereen Ezzat, … , Gillian E. Wu, Sylvia L. Asa
Published January 1, 2002
Citation Information: J Clin Invest. 2002;109(1):69-78. https://doi.org/10.1172/JCI14036.
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Article

Targeted expression of a human pituitary tumor–derived isoform of FGF receptor-4 recapitulates pituitary tumorigenesis

Abstract

It is estimated that up to one in five individuals develop pituitary gland tumors. Despite the common occurrence of these tumors, the pathogenetic mechanisms underlying their development remain largely unknown. We report the identification of a novel pituitary tumor–derived, N-terminally truncated isoform of FGF receptor-4 (ptd-FGFR4). The corresponding mRNA results from alternative transcription initiation and encodes a polypeptide that lacks a signal peptide and the first two extracellular Ig-like domains. ptd-FGFR4 has a distinctive cytoplasmic residence, is constitutively phosphorylated, and is transforming in vitro and in vivo. Here we show that targeted expression of ptd-FGFR4, but not FGFR4, results in pituitary tumors that morphologically recapitulate the human disease.

Authors

Shereen Ezzat, Lei Zheng, Xian-Feng Zhu, Gillian E. Wu, Sylvia L. Asa

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Figure 3

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Phosphotyrosine activity of FGFR4 and ptd-FGFR4. Transiently transfected...
Phosphotyrosine activity of FGFR4 and ptd-FGFR4. Transiently transfected HEK 293 cells (a) and stably transfected NIH 3T3 cells (b and c) were exposed to FGF-1 (50 ng/ml; a and c). Equal amounts of protein were immunoprecipitated with an antibody directed against the C-terminus of FGFR4 and electrophoresed. (a) In HEK 293 cells, immunoblotting with anti-phosphotyrosine identifies a 110-kDa fragment only after exposure to FGF-1 in cells transfected with full-length FGFR4 (upper arrow). Cells transfected with empty vector (pcDNA) are negative. Cells expressing ptd-FGFR4 exhibit phosphorylation of the 65-kDa isoform with and without FGF-1 treatment, consistent with constitutive phosphorylation of the truncated receptor (lower arrow). (b) NIH 3T3 cells stably transfected with FGFR4 express large amounts of the 110/90-kDa protein (upper arrow), and those stably transfected with ptd-FGFR4 express the 65-kDa protein (lower arrow); cells transfected with empty vector are negative. (c) NIH 3T3 cells transfected with empty vector (pcDNA, right) express endogenous FGFR4 that migrates at 110 kDa and is detected with phosphotyrosine (pTYR) antibody after exposure to FGF-1 (upper arrow). Cells transfected with FGFR4 (left) exhibit the same pattern, but with greater intensity (documented by densitometry). Cells transfected with ptd-FGFR4 (middle) express a 65-kDa protein that is phosphorylated in the presence and absence of FGF-1 (lower arrow); these cells also express the 110-kDa protein, and phosphorylation of this endogenous receptor is enhanced in the presence of FGF-1 to a greater degree than in control cells. These transfected NIH 3T3 cells had FGFR4 immunoreactivity that comigrated with the pTYR-immunoreactive bands.