Identification of TGFß-induced proteins in non-endocrine mouse pituitary cell line TtT/GF by SILAC-assisted quantitative mass spectrometry.

ABSTRACT

TtT/GF is a mouse cell line derived from a thyrotropic pituitary tumor and has been used as a model of folliculostellate cells. Our previous microarray data indicate that TtT/GF possesses some properties of endothelial cells, pericytes and stem/progenitor cells, along with folliculostellate cells, suggesting its plasticity. We also found that transforming growth factor beta (TGFß) alters cell motility, increases pericyte marker transcripts and attenuates endothelial cell and stem/progenitor cell markers in TtT/GF cells. The present study explores the wide-range effect of TGFß on TtT/GF cells at the protein level and characterizes TGFß-induced proteins and their partnerships using stable isotope labeling of amino acids in cell culture (SILAC)-assisted quantitative mass spectrometry. Comparison between quantified proteins from TGFß-treated cells and those from SB431542 (a selective TGFß receptor I inhibitor)-treated cells revealed 51 upregulated and 112 downregulated proteins (|log2| > 0.6). Gene ontology and STRING analyses revealed that these are related to the actin cytoskeleton, cell adhesion, extracellular matrix and DNA replication. Consistently, TGFß-treated cells showed a distinct actin filament pattern and reduced proliferation compared to vehicle-treated cells; SB431542 blocked the effect of TGFß. Upregulation of many pericyte markers (CSPG4, NES, ACTA, TAGLN, COL1A1, THBS1, TIMP3 and FLNA) supports our previous hypothesis that TGFß reinforces pericyte properties. We also found downregulation of CTSB, EZR and LGALS3, which are induced in several pituitary adenomas. These data provide valuable information about pericyte differentiation as well as the pathological processes in pituitary adenomas.