RESUMEN
A 6.8-kDa proteolipid (called MLQ) is a hydrophobic mitochondrial protein with unknown function that is loosely associated with ATP synthase. Here, we show that MLQ-knockdown HeLa cells lose population of ATP synthase in mitochondria. This is not due to low transcription of subunit genes of ATP synthase because levels of mRNA for α- and ß-subunits are unaffected by the knockdown. As a consequence, the knockdown cells show low mitochondrial ATP synthesis activity, grow slowly in the normal medium, and are vulnerable to glucose deprivation. Given that the expression of MLQ varies responding to cellular conditions, MLQ is a potential regulator of the mitochondrial ATP synthesis.
Asunto(s)
Mitocondrias/metabolismo , Proteínas Mitocondriales/metabolismo , Proteolípidos/metabolismo , ATPasas de Translocación de Protón/metabolismo , Aumento de la Célula , Supervivencia Celular , Proteínas del Complejo de Cadena de Transporte de Electrón/metabolismo , Células HeLa , Humanos , Potencial de la Membrana Mitocondrial , Mitocondrias/genética , Proteínas Mitocondriales/genética , ATPasas de Translocación de Protón Mitocondriales , Proteolípidos/genética , ATPasas de Translocación de Protón/genética , ARN Mensajero/metabolismoRESUMEN
It was found recently that a diabetes-associated protein in insulin-sensitive tissue (DAPIT) is associated with mitochondrial ATP synthase. Here, we report that the suppressed expression of DAPIT in DAPIT-knockdown HeLa cells causes loss of the population of ATP synthase in mitochondria. Consequently, DAPIT-knockdown cells show smaller mitochondrial ATP synthesis activity, slower growth in normal medium, and poorer viability in glucose-free medium than the control cells. The mRNA levels of α- and ß-subunits of ATP synthase remain unchanged by DAPIT knockdown. These results indicate a critical role of DAPIT in maintaining the ATP synthase population in mitochondria and raise an intriguing possibility of active role of DAPIT in cellular energy metabolism.
Asunto(s)
Metabolismo Energético/fisiología , Proteínas de la Membrana/metabolismo , Mitocondrias/enzimología , Proteínas Mitocondriales/metabolismo , ATPasas de Translocación de Protón Mitocondriales/metabolismo , ARN Mensajero/metabolismo , Técnicas de Silenciamiento del Gen , Células HeLa , Humanos , Proteínas de la Membrana/genética , Mitocondrias/genética , Proteínas Mitocondriales/genética , ATPasas de Translocación de Protón Mitocondriales/genética , ARN Mensajero/genéticaRESUMEN
Apoptosis-inducing factor (AIF) is a mitochondrial intermembrane flavoprotein that is translocated to the nucleus in response to proapoptotic stimuli, where it induces nuclear apoptosis. Here we show that AIF is synthesized as an approximately 67-kDa preprotein with an N-terminal extension and imported into mitochondria, where it is processed to the approximately 62-kDa mature form. Topology analysis revealed that mature AIF is a type-I inner membrane protein with the N-terminus exposed to the matrix and the C-terminal portion to the intermembrane space. Upon induction of apoptosis, processing of mature AIF to an approximately 57-kDa form occurred caspase-independently in the intermembrane space, releasing the processed form into the cytoplasm. Bcl-2 or Bcl-XL inhibited both these events. These findings indicate that AIF release from mitochondria occurs by a two-step process: detachment from the inner membrane by apoptosis-induced processing in the intermembrane space and translocation into the cytoplasm. The results also suggest the presence of a unique protease that is regulated by proapoptotic stimuli in caspase-independent cell death.