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Activated Rac1 regulates the degradation of I?B? and the nuclear translocation of STAT3-NF?B complexes in starved cancer cells.

ABSTRACT: In several human tumors, signal transducer and activator of transcription 3 (STAT3) and nuclear factor ?B (NF?B) are activated and interact; how these STAT3-NF?B complexes are transported to the nucleus is not fully understood. In this study, we found that Rac1 was activated in starved cancer cells and that activated Rac1 coexisted with STAT3 and NF?B. Rac1 knockdown and overexpression of the dominant-negative mutant Rac1N19 inhibited the degradation of I?B?, an inhibitor of NF?B. MG132, an inhibitor of the ubiquitin proteasome pathway, increased the amount of non-phosphorylated I?B?, but not serine-phosphorylated I?B?, indicating that I?B? degradation by Rac1 in starved cancer cells is independent of I?B? serine phosphorylation by IKK. Rac1 knockdown also inhibited the nuclear translocation of STAT3-NF?B complexes, indicating that this translocation requires activated Rac1. We also demonstrated that the mutant STAT3 Y705F could form complexes with NF?B, and these unphosphorylated STAT3-NF?B complexes translocated into the nucleus and upregulated the activity of NF?B in starved cancer cells, suggesting that phosphorylation of STAT3 is not essential for its translocation. To our knowledge, this is the first study demonstrating the crucial role of Rac1 in the function of STAT3-NF?B complexes in starved cancer cells and implies that targeting Rac1 may have future therapeutic significance in cancer therapy.

SUBMITTER: Kim SJ

PROVIDER: S-EPMC4910147 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Activated Rac1 regulates the degradation of IκBα and the nuclear translocation of STAT3-NFκB complexes in starved cancer cells.

Kim Sung Joo SJ Yoon Sarah S

Experimental & molecular medicine 20160506

In several human tumors, signal transducer and activator of transcription 3 (STAT3) and nuclear factor κB (NFκB) are activated and interact; how these STAT3-NFκB complexes are transported to the nucleus is not fully understood. In this study, we found that Rac1 was activated in starved cancer cells and that activated Rac1 coexisted with STAT3 and NFκB. Rac1 knockdown and overexpression of the dominant-negative mutant Rac1N19 inhibited the degradation of IκBα, an inhibitor of NFκB. MG132, an inhi ...[more]

PMID: 27151455

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Project description:BackgroundUbiquitin-fold modifier-1 (Ufm1) is a recently identified ubiquitin-like protein. We previously confirmed that Ufm1 expression was increased in diabetic mice. However, its role in the development of diabetes remains undefined.MethodsLentivirus-mediated gene knockdown and overexpression techniques were used to observe the effect of Ufm1 on the expression of inflammatory factors, adhesion molecules and chemokines, as well as the transcriptional activity of nuclear factor kappa-B (NF-κB) in macrophages. Western blot and immunofluorescence analyses were used to analyse the mechanism by which Ufm1 affects the transcriptional activity of NF-κB. Finally, the effects of Ufm1 on inflammation and pancreatic, renal and myocardial damage were observed in db/db mice.ResultsKnockdown of Ufm1 by lentivirus shRNA targeting Ufm1 (Lv-shUfm1) led to decreased secretion of IL-6, IL-1β, ICAM-1, VCAM-1, MCP-1 and CXCL2 in RAW264.7 cells that were exposed to LPS and TNF-α, while lentiviral overexpression of Ufm1 (Lv-Ufm1) caused the opposite effect. Interestingly, further investigation indicated that Ufm1 induced NF-κB p65 nuclear translocation in RAW264.7 cells via increasing the ubiquitination and degradation of IκBα. In an in vivo experiment, pretreatment of db/db mice with Lv-shUfm1 reduced the mRNA levels of TNF-α, IL-6, IL-1β, ICAM-1, VCAM-1, MCP-1 and CXCL2 in resident peritoneal macrophages (RPMs) and decreased the plasma levels of TNF-α, IL-6, IL-1β, ICAM-1, VCAM-1, MCP-1 and CXCL2. Additionally, in Lv-Ufm1-treated mice, the inverse results were observed. Following treatment with Lv-shUfm1 and Lv-Ufm1, NF-κB p65 nuclear translocation in RPMs was decreased and increased, respectively. Importantly, we observed that Lv-shUfm1 injection led to a decrease in plasma glycaemia, a reduction in urinary albuminuria and cardiomyocyte hypertrophy and an improvement in the histopathological appearance of pancreatic, kidney and myocardial tissue. Pretreatment of the mice with Lv-shUfm1 inhibited macrophage infiltration in the pancreas, kidney and myocardial tissue.ConclusionOur data elucidate a new biological function of Ufm1 that mediates inflammatory responses. Ufm1-mediated p65 nuclear translocation occurs by modulating the ubiquitination and degradation of IκBα. Moreover, downregulating Ufm1 is an effective strategy to prevent the development of type 2 diabetes and its complications.

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Dataset Information

Activated Rac1 regulates the degradation of I?B? and the nuclear translocation of STAT3-NF?B complexes in starved cancer cells.

Publications

Activated Rac1 regulates the degradation of IκBα and the nuclear translocation of STAT3-NFκB complexes in starved cancer cells.

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