Transcription Factors NRF2 and NF-κB Are Coordinated Effectors of the Rho Family, GTP-binding Protein RAC1 during Inflammation

Background: RAC1 is a small G-protein of the Rho family that activates the transcription factor NF-B to elicit an inflammatory response. Results: We have found that RAC1 also induces the NRF2/ARE pathway, which in term blocks RAC1-dependent NF-B activation. Conclusion: RAC1 modulates inflammation by coordinating the activity of pro-inflammatory NF-B and anti-oxidant NRF2 transcription factors. Significance: Therapeutic intervention on RAC1 could help modulate pro- and anti-inflammatory processes. The small GTPase protein RAC1 participates in innate immunity by activating a complex program that includes cytoskeleton remodeling, chemotaxis, activation of NADPH oxidase, and modulation of gene expression. However, its role in regulating the transcriptional signatures that in term control the cellular inflammatory profiles are not well defined. Here we investigated the functional and mechanistic connection between RAC1 and the transcription factor NRF2 (nuclear factor erythroid 2-related factor 2), master regulator of the anti-oxidant response. Lipopolysaccharide and constitutively active RAC1(Q61L) mutant induced the anti-oxidant enzyme heme-oxygenase-1 (HO-1) through activation of NRF2. The use of KEAP1-insensitive NRF2 mutants indicated that RAC1 regulation of NRF2 is KEAP1-independent. Interestingly, NRF2 overexpression inhibited, whereas a dominant-negative mutant of NRF2 exacerbated RAC1-dependent activation of nuclear factor-B (NF-B), suggesting that NRF2 has an antagonistic effect on the NF-B pathway. Moreover, we found that RAC1 acts through NF-B to induce NRF2 because either expression of a dominant negative mutant of IB that leads to NF-B degradation or the use of p65-NF-B-deficient cells demonstrated lower NRF2 protein levels and basally impaired NRF2 signature compared with control cells. In contrast, NRF2-deficient cells showed increased p65-NF-B protein levels, although the mRNA levels remain unchanged, indicating post-translational alterations. Our results demonstrate a new mechanism of modulation of RAC1 inflammatory pathway through a cross-talk between NF-B and NRF2.