IKKα contributes to UVB-induced VEGF expression by regulating AP-1 transactivation

Abstract

Exposure to ultraviolet B (UVB) irradiation from sunlight induces the upregulation of VEGF, a potent angiogenic factor that is critical for mediating angiogenesis-associated photodamage. However, the molecular mechanisms related to UVB-induced VEGF expression have not been fully defined. Here, we demonstrate that one of the catalytic subunits of the IκB kinase complex (IKK), IKKα, plays a critical role in mediating UVB-induced VEGF expression in mouse embryonic fibroblasts (MEFs), which requires IKKα kinase activity but is independent of IKKβ, IKKγ and the transactivation of NF-κB. We further show that the transcriptional factor AP-1 functions as the downstream target of IKKα that is responsible for VEGF induction under UVB exposure. Both the accumulation of AP-1 component, c-Fos and the transactivation of AP-1 by UVB require the activated IKKα located within the nucleus. Moreover, nuclear IKKα can associate with c-Fos and recruit to the vegf promoter regions containing AP-1-responsive element and then trigger phosphorylation of the promoter-bound histone H3. Thus, our results have revealed a novel independent role for IKKα in controlling VEGF expression during the cellular UVB response by regulating the induction of the AP-1 component and phosphorylating histone H3 to facilitate AP-1 transactivation. Targeting IKKα shows promise for the prevention of UVB-induced angiogenesis and the associated photodamage.

p85 mediates NFAT3-dependent VEGF induction in the cellular UVB response

“…Moreover, taken together with our previous study (Dong et al, 2012), the induced interaction between NFAT3 and c-Fos, indicates a synergistic effect and convergence of IKKa-AP-1 and p85a-NFAT3 signaling pathways on UVB-induced VEGF expression. Therefore, our findings contribute to a greater understand of the signaling events that regulate skin angiogenesis following UVB irradiation and might provide a new approach for the prevention of angiogenesis-related skin damage by targeting p85a or IKKa.…”

“…We demonstrated in our recent study that UVB exposure induces a significant increase of VEGF expression in the mouse fibroblasts, which is mediated by IKKa-dependent AP-1 transactivation (Dong et al, 2012). Since p85a has been proved to play a crucial role in regulating p53 transactivation and TNFa expression, and therefore mediate both DNA damage and inflammatory injury under UVB irradiation (Song et al, 2011;Song et al, 2007), we next wanted to address whether p85a also contributes to VEGF expression and therefore participates in the angiogenesis-associated photodamage.…”

“…The FLAG-NFAT3 expression plasmid was provided by Dr Qinong Ye (Beijing Institute of Biotechnology, China). NFAT3 and c-Fos shRNA expression plasmid were described in our previous studies (Dong et al, 2012;Song et al, 2007). GFP-p85a expression plasmid was described in our previous study.…”

“…VEGF production in the cell culture supernatants was quantified using a mouse VEGF immunoassay kit (R&D Systems, Inc., Minneapolis, MN) as described previously (Dong et al, 2012).…”

“…Cell lysates were immunoprecipitated with an anti-GFP antibody and then the immunoprecipitants were subjected to a western blot assay with an anti-FLAG and anti-NFAT3 antibodies. The signals were detected as described in our previous reports (Dong et al, 2012;Song et al, 2011).…”