Engulfment Protein GULP Is Regulator of Transforming Growth Factor-β Response in Ovarian Cells

Cheng-I J Ma,Cyril Martin,Zhong Ma,Anouar Hafiane,Meiou Dai,Jean-Jacques Lebrun,Robert S Kiss

doi:10.1074/jbc.m111.314997

Cheng-I J Ma, Cyril Martin + Show 5 more

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https://doi.org/10.1074/jbc.m111.314997

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Abstract

Transforming growth factor β (TGF-β) is a key regulatory molecule with pleiotropic effects on cell growth, migration, and invasion. As a result, impairment of proper TGF-β signaling is central to tumorigenesis and metastasis. The TGF-β receptor V (TGFBRV or LRP1) has been shown to be responsible for TGF-β-mediated cell growth inhibition in Chinese hamster ovary (CHO) cells. The LRP1 adapter protein GULP mediates internalization of the various LRP1-specific ligands, and we hypothesize that GULP acts as a novel regulator of TGF-β signaling in ovarian cells. CHO cells that overexpress exogenous GULP (FL) demonstrate enhancement in growth inhibition, migration, and invasion from TGF-β treatment, whereas cells that lack GULP (AS) show impairment of growth inhibition and decreased migration and invasion. The enhanced TGF-β response in FL cells was confirmed by a prolonged TGF-β-induced SMAD3 phosphorylation, whereas a shortening of the phosphorylation event is observed in AS cells. Mechanistically, the presence of GULP retains the TGF-β in a signaling-competent early endosome for enhanced signaling. To address this mechanism in a physiological setting, TGF-β insensitive ovarian adenocarcinoma cells (HEY) have a very low GULP expression level, similar to the observation made in a wide selection of human ovarian adenocarcinomas. Transfection of GULP into the HEY cells restored the TGF-β responsiveness, as measured by SMAD3 phosphorylation and impairment of cell growth. Because GULP expression positively regulates TGF-β signaling leading to growth inhibition, this may represent an attractive target to achieve TGF-β responsiveness in ovarian cells.

Highlights

The low density lipoprotein receptor-related protein 1 (LRP1) is a transforming growth factor ␤ (TGF-␤) receptor in ovarian cells
We have previously described the effect of the phosphotyrosine binding domain (PTB)-containing engulfment adapter protein (GULP), an adapter protein of LRP1, on cellular lipid homeostasis by modulating the endocytosis of LRP1 and LRP ligands [41]
We present evidence that GULP is required in ovarian cells to maintain their sensitivity toward TGF-␤-induced cell growth arrest, demonstrating the important role that GULP may perform in ovarian cancer progression

Summary

Introduction

The low density lipoprotein receptor-related protein 1 (LRP1) is a transforming growth factor ␤ (TGF-␤) receptor in ovarian cells. Results: GULP is an adapter to LRP1 and mediates TGF-␤ signaling in signaling-competent early endosomes. The TGF-␤ receptor V (TGFBRV or LRP1) has been shown to be responsible for TGF␤-mediated cell growth inhibition in Chinese hamster ovary (CHO) cells. The presence of GULP retains the TGF-␤ in a signaling-competent early endosome for enhanced signaling. To address this mechanism in a physiological setting, TGF-␤ insensitive ovarian adenocarcinoma cells (HEY) have a very low GULP expression level, similar to the observation made in a wide selection of human ovarian adenocarcinomas. Because GULP expression positively regulates TGF-␤ signaling leading to growth inhibition, this may represent an attractive target to achieve TGF-␤ responsiveness in ovarian cells

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