RESUMO
The Golgi stress response is a homeostatic mechanism that controls the capacity of the Golgi apparatus in accordance with cellular demands. When the capacity of the Golgi apparatus becomes insufficient (Golgi stress), transcription levels of Golgi-related genes encoding glycosylation enzymes, a Golgi structural protein, and components of vesicular transport are upregulated through a common cis-acting enhancer-the Golgi apparatus stress response element (GASE). Here, we identified the transcription factor MLX as a GASE-binding protein. MLX resides in the cytoplasm and does not bind to GASE in normal growth conditions, whereas MLX translocates into the nucleus and specifically binds to GASE in response to Golgi stress. Suppression of MLX expression increased transcriptional induction of target genes of the Golgi stress response, whereas overexpression of MLX reduced GASE-binding of TFE3 as well as transcriptional induction from GASE, suggesting that MLX is a transcriptional repressor of the mammalian Golgi stress response.
Assuntos
Fatores de Transcrição de Zíper de Leucina e Hélice-Alça-Hélix Básicos/metabolismo , Complexo de Golgi/metabolismo , Fatores de Transcrição de Zíper de Leucina e Hélice-Alça-Hélix Básicos/antagonistas & inibidores , Fatores de Transcrição de Zíper de Leucina e Hélice-Alça-Hélix Básicos/genética , Northern Blotting , Imunoprecipitação da Cromatina , Regulação da Expressão Gênica/genética , Genes Reporter/genética , Complexo de Golgi/genética , Células HeLa , Humanos , Imuno-Histoquímica , Microscopia de Fluorescência , Ligação Proteica , Interferência de RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Interferente Pequeno/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Elementos de Resposta/genéticaRESUMO
The Golgi stress response is a mechanism by which, under conditions of insufficient Golgi function (Golgi stress), the transcription of Golgi-related genes is upregulated through an enhancer, the Golgi apparatus stress response element (GASE), in order to maintain homeostasis in the Golgi. The molecular mechanisms associated with GASE remain to be clarified. Here, we identified TFE3 as a GASE-binding transcription factor. TFE3 was phosphorylated and retained in the cytoplasm in normal growth conditions, whereas it was dephosphorylated, translocated to the nucleus and activated Golgi-related genes through GASE under conditions of Golgi stress, e.g. in response to inhibition of oligosaccharide processing in the Golgi apparatus. From these observations, we concluded that the TFE3-GASE pathway is one of the regulatory pathways of the mammalian Golgi stress response, which regulates the expression of glycosylation-related proteins in response to insufficiency of glycosylation in the Golgi apparatus.
Assuntos
Fatores de Transcrição de Zíper de Leucina e Hélice-Alça-Hélix Básicos/metabolismo , Complexo de Golgi/genética , Complexo de Golgi/metabolismo , Elementos de Resposta , Transporte Ativo do Núcleo Celular , Núcleo Celular/metabolismo , Glicosilação , Células HeLa , Humanos , Metabolismo dos Lipídeos , Estresse Oxidativo/genética , Fosforilação , Proteoglicanas/metabolismo , Transcrição Gênica , Ativação TranscricionalRESUMO
When increased production of secretory proteins overwhelms the capacity of the endoplasmic reticulum (ER) and the Golgi apparatus, eukaryotic cells expand their capacity to sustain secretory function. The capacity of the ER is enhanced by the mechanism called the ER stress response, but the mechanism regulating Golgi capacity (the Golgi stress response) has remained unclear. Here, we found that transcription of Golgi-related genes, including glycosylation enzymes as well as factors involved in post-Golgi vesicular transport and maintenance of Golgi structure, was upregulated upon treatment with monensin, an ionophore that disrupts the function of acidic organelles, including the Golgi apparatus and lysosomes by neutralizing their lumen. This transcriptional induction was found to be commonly regulated by a novel cis-acting element called the Golgi apparatus stress response element (GASE), whose consensus sequence is ACGTGgc. When the function of the Golgi apparatus was specifically disturbed by overexpression of GCP60, a Golgi-localized protein that binds to giantin, transcription from GASE was significantly induced. These results suggest that mammalian cells have the Golgi stress response, and that GASE regulates transcriptional induction involved in the Golgi stress response.