RESUMO
The ubiquitin-proteasome system is the major pathway of non-lysosomal intracellular protein degradation, playing an important role in a variety of cellular responses including cell division, proliferation, and apoptosis. Ubiquitin-specific protease 14 (USP14) is a component of proteasome regulatory subunit 19 S that regulates deubiquitinated proteins entering inside the proteasome core 20 S. The role of USP14 in protein degradation is still controversial. Several studies suggest that USP14 plays an inhibitory role in protein degradation. Here, in contrast, overexpression of USP14 induced I-κB degradation, which increased cytokine release in lung epithelial cells. Overexpression of HA-tagged USP14 (HA-USP14) reduced I-κB protein levels by increasing the I-κB degradation rate in mouse lung epithelial cells (MLE12). I-κB polyubiquitination was reduced in HA-USP14-overexpressed MLE12 cells, suggesting that USP14 regulates I-κB degradation by removing its ubiquitin chain, thus promoting the deubiquitinated I-κB degradation within the proteasome. Interestingly, we found that USP14 was associated with RelA, a binding partner of I-κB, suggesting that RelA is the linker between USP14 and I-κB. Lipopolysaccharide (LPS) treatment induced serine phosphorylation of USP14 as well as further reducing I-κB levels in HA-USP14-overexpressed MLE12 cells as compared with empty vector transfected cells. Further, overexpression of HA-USP14 increased the LPS-, TNFα-, or Escherichia coli-induced IL-8 release in human lung epithelial cells. This study suggests that USP14 removes the ubiquitin chain of I-κB, therefore inducing I-κB degradation and increasing cytokine release in lung epithelial cells.
Assuntos
Células Epiteliais/metabolismo , Proteínas I-kappa B/metabolismo , Interleucina-8/metabolismo , Pulmão/metabolismo , Proteólise , Mucosa Respiratória/metabolismo , Fator de Necrose Tumoral alfa/metabolismo , Ubiquitina Tiolesterase/biossíntese , Animais , Linhagem Celular , Células Epiteliais/citologia , Escherichia coli , Humanos , Proteínas I-kappa B/genética , Interleucina-8/genética , Lipopolissacarídeos/farmacologia , Pulmão/citologia , Camundongos , Fosforilação/efeitos dos fármacos , Fosforilação/genética , Mucosa Respiratória/citologia , Fator de Transcrição RelA/genética , Fator de Transcrição RelA/metabolismo , Fator de Necrose Tumoral alfa/genética , Ubiquitina/genética , Ubiquitina/metabolismo , Ubiquitina Tiolesterase/genética , Ubiquitinação/efeitos dos fármacos , Ubiquitinação/genéticaRESUMO
The ST2L receptor for interleukin 33 (IL-33) mediates pulmonary inflammation and immune system-related disorders, such as asthma and rheumatoid arthritis. At present, very little is known about the molecular regulation of ST2L expression. Here we found that FBXL19, an 'orphan' member of the Skp1-Cullin-F-box family of E3 ubiquitin ligases, selectively bound to ST2L to mediate its polyubiquitination and elimination in the proteasome. Degradation of ST2L involved phosphorylation of ST2L at Ser442 catalyzed by the kinase GSK3ß. Overexpression of FBXL19 abrogated the proapoptotic and inflammatory effects of IL-33 and lessened the severity of lung injury in mouse models of pneumonia. Our results suggest that modulation of the IL-33-ST2L axis by ubiquitin ligases might serve as a unique strategy for lessening pulmonary inflammation.
