The role of beta-arrestin 2 in lysophosphatidic acid-induced NF-kappaB activation.

摘要

Lysophosphatidic acid (LPA) is a bioactive phospholipid and binds to its receptors, a family of G protein-coupled receptors (GPCR), which initiates multiple signaling cascades and leads to activation of several transcription factors, including NF-kappaB. NF-kappaB critically regulates numerous gene expressions, and is persistently active in many diseases. In our previous studies, we have demonstrated that LPA-induced NF-kappaB activation is dependent on a novel scaffold protein, CARMA3. However, how CARMA3 is recruited to receptor remains unknown. beta-Arrestins are a family of proteins involved in desensitization of GPCR signaling. Additionally, beta-arrestins function as signaling adaptor proteins, and mediate multiple signaling pathways. Therefore, we have hypothesized that beta-arrestins may link CARMA3 to LPA receptors, and facilitate LPA-induced NF-kappaB activation.;Using beta-arrestin-deficient MEFs, we found that beta-arrestin 2, but not beta-arrestin 1, was required for LPA-induced NF-kappaB activation. Also, we showed that the expression of NF-kappaB-dependent cytokines, such as interlukin-6, was impaired in beta-arrestin 2-deficient MEFs. Mechanistically, we demonstrated the inducible association of endogenous beta-arrestin 2 and CARMA3, and we found the CARD domain of CARMA3 interacted with 60-320 residues of beta-arrestin 2. To understand why beta-arrestin 2, but not beta-arrestin 1, mediated NF-kappaB activation, we generated beta-arrestin mutants. However, some mutants degraded quickly, and the rest did not rescue NF-kappaB activation in beta-arrestin-deficient MEFs, though they had similar binding affinities with CARMA3. Therefore, it indicates that slight changes in residues may determine the different functions of beta-arrestins. Moreover, we found beta-arrestin 2 deficiency impaired LPA-induced IKK kinase activity, while it did not affect LPA-induced IKKalpha/beta phosphorylation.;In summary, our results provide the genetic evidence that beta-arrestin 2 serves as a positive regulator in NF-kappaB signaling pathway by connecting CARMA3 to LPA receptors. Additionally, we demonstrate that beta-arrestin 2 is required for IKKalpha/beta activation, but not for the inducible phosphorylation of IKKalpha/beta. Because the signaling pathways around the membrane-proximal region of LPA receptors and GPCRs are quite conserved, our results also suggest a possible link between other GPCRs and CARMA3-mediated NF-kappaB activation. To fully define the role of beta-arrestins in LPA-induced NF-kappaB signaling pathways will help to identify new drug targets for clinical therapeutics.