RESUMO
Glutamine is an essential nutrient for cancer cell survival and proliferation, yet the signaling pathways that sense glutamine levels remain uncharacterized. Here, we report that the protein phosphatase 2A (PP2A)-associated protein, α4, plays a conserved role in glutamine sensing. α4 promotes assembly of an adaptive PP2A complex containing the B55α regulatory subunit via providing the catalytic subunit upon glutamine deprivation. Moreover, B55α is specifically induced upon glutamine deprivation in a ROS-dependent manner to activate p53 and promote cell survival. B55α activates p53 through direct interaction and dephosphorylation of EDD, a negative regulator of p53. Importantly, the B55α-EDD-p53 pathway is essential for cancer cell survival and tumor growth under low glutamine conditions in vitro and in vivo. This study delineates a previously unidentified signaling pathway that senses glutamine levels as well as provides important evidence that protein phosphatase complexes are actively involved in signal transduction.
Assuntos
Glutamina/deficiência , Proteína Fosfatase 2/metabolismo , Subunidades Proteicas/metabolismo , Estresse Fisiológico , Proteína Supressora de Tumor p53/metabolismo , Adaptação Fisiológica , Proteínas Adaptadoras de Transdução de Sinal , Animais , Domínio Catalítico , Linhagem Celular Tumoral , Proliferação de Células , Sobrevivência Celular , Expressão Gênica , Técnicas de Silenciamento de Genes , Células HEK293 , Humanos , Peptídeos e Proteínas de Sinalização Intercelular , Masculino , Camundongos , Camundongos Nus , Chaperonas Moleculares , Células NIH 3T3 , Transplante de Neoplasias , Neoplasias Experimentais/metabolismo , Neoplasias Experimentais/patologia , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Multimerização Proteica , Proteína Fosfatase 2/genética , Proteína Fosfatase 2/fisiologia , Subunidades Proteicas/genética , Subunidades Proteicas/fisiologia , RNA Interferente Pequeno/genética , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Ativação Transcricional , Carga Tumoral , Ubiquitina-Proteína Ligases/metabolismoRESUMO
Despite advances in our understanding of protein kinase regulation in the DNA damage response, the mechanism that controls protein phosphatase activity in this pathway is unclear. Unlike kinases, the activity and specificity of serine/threonine phosphatases is governed largely by their associated proteins. Here we show that Tip41-like protein (TIPRL), an evolutionarily conserved binding protein for PP2A-family phosphatases, is a negative regulator of protein phosphatase 4 (PP4). Knockdown of TIPRL resulted in increased PP4 phosphatase activity and formation of the active PP4-C/PP4R2 complex known to dephosphorylate γ-H2AX. Thus, overexpression of TIPRL promotes phosphorylation of H2AX, and increases γ-H2AX positive foci in response to DNA damage, whereas knockdown of TIPRL inhibits γ-H2AX phosphorylation. In correlation with γ-H2AX levels, we found that TIPRL overexpression promotes cell death in response to genotoxic stress, and knockdown of TIPRL protects cells from genotoxic agents. Taken together, these data demonstrate that TIPRL inhibits PP4 activity to allow for H2AX phosphorylation and the subsequent DNA damage response.