p38δ controls Mitogen- and Stress-activated Kinase-1 (MSK1) function in response to toll-like receptor activation in macrophages.

Mitogen- and Stress-activated Kinase (MSK) 1 is a nuclear protein, activated by p38α Mitogen-Activated Kinase (MAPK) and extracellular signal-regulated kinase (ERK1/2), that modulate the production of certain cytokines in macrophages. Using knockout cells and specific kinase inhibitors, we show that, besides p38α and ERK1/2, another p38MAPK, p38δ, mediates MSK phosphorylation and activation, in LPS-stimulated macrophages. Additionally, recombinant MSK1 was phosphorylated and activated by recombinant p38δ, to the same extent than by p38α, in in vitro experiments. Moreover, the phosphorylation of the transcription factors CREB and ATF1, that are MSK physiological substrates, and the expression of the CREB-dependent gene encoding DUSP1, were impaired in p38δ-deficient macrophages. Also, the transcription of IL-1Ra mRNA, that is MSK-dependent, was reduced. Our results indicate that MSK activation can be one possible mechanism by which p38δ regulates the production of a variety of inflammatory molecules involved in immune innate response.

The p38-interacting protein p38IP suppresses TCR and LPS signaling by targeting TAK1.

Negative regulation of immunoreceptor signaling is required for preventing hyperimmune activation and maintaining immune homeostasis. The roles of p38IP in immunoreceptor signaling remain unclear. Here, we show that p38IP suppresses T-cell receptor (TCR)/LPS-activated NF-κB and p38 by targeting TAK1 kinase and that p38IP protein levels are downregulated in human PBMCs from rheumatoid arthritis (RA) patients, inversely correlating with the enhanced activity of NF-κB and p38. Mechanistically, p38IP interacts with TAK1 to disassemble the TAK1-TAB (TAK1-binding protein) complex. p38IP overexpression decreases TCR-induced binding of K63-linked polyubiquitin (polyUb) chains to TAK1 but increases that to TAB2, and p38IP knockdown shows the opposite effects, indicating unanchored K63-linked polyUb chain transfer from TAB2 to TAK1. p38IP dynamically interacts with TAK1 upon stimulation, because of the polyUb chain transfer and the higher binding affinity of TAK1 and p38IP for polyUb-bound TAB2 and TAK1, respectively. Moreover, p38IP scaffolds the deubiquitinase USP4 to deubiquitinate TAK1 once TAK1 is activated. These findings reveal a novel role and the mechanisms of p38IP in controlling TCR/LPS signaling and suggest that p38IP might participate in RA pathogenesis.

p38 MAPK mediates epithelial-mesenchymal transition by regulating p38IP and Snail in head and neck squamous cell carcinoma.

BACKGROUND: In the present study, we investigated the role of p38-p38IP signaling in the inflammation-induced promotion of epithelial-to-mesenchymal transition (EMT) in Head and Neck Squamous Cell Carcinoma (HNSCC). METHODS: Quantitative RT-PCR, western blot analysis, spheroid modeling and immunohistochemical staining of human HNSCC tissue sections were used. RESULTS: p38 inhibitor treated and p38 shRNA HNSCC cell lines demonstrate a significant upregulation in E-cadherin mRNA and a decrease in the mRNA expression of Snail. p38 binds to and stabilizes p38IP, a subunit of histone SPT3-TAF9-GCN5 acetyltransferase (STAGA), resulting in enhanced transcription of Snail. p38 shRNA HNSCC cell lines show a less invasive phenotype in a spheroid model. In clinical HNSCC samples, p38 interacting protein (p38IP) is significantly increased compared to adjacent normal tissue. An inverse relationship between p38, p38IP and E-cadherin is demonstrated. CONCLUSIONS: Herein we provide the first report that p38-p38IP is required for the Snail-induced E-cadherin down-regulation and cell invasion in HNSCC.

A novel miR-200b-3p/p38IP pair regulates monocyte/macrophage differentiation.

Monocyte/macrophage differentiation represents a major branch of hematopoiesis and is a central event in the immune response, but the molecular mechanisms underlying are not fully delineated. Here we show that p38 mitogen-activated protein kinase (MAPK) interacting protein (p38IP) is downregulated during monocyte/macrophage differentiation in vitro. Overexpression of p38IP halted monocyte/macrophage differentiation, whereas forward knockdown of p38IP by RNA interference induced G1/S arrest and promoted monocyte differentiation into macrophages and the maturation of macrophages as well. Moreover, we found that miR-200b-3p was upregulated during monocyte/macrophage differentiation and mediated the downregulation of p38IP by binding to the 3' untranslated terminal region of p38IP mRNA. Overexpression of a miR-200b-3p mimic resembled the effect of p38IP knockdown, whereas a miR-200b-3p inhibitor blocked monocyte/macrophage differentiation by enhancing p38IP expression. Further western blotting analysis revealed that p38IP downregulation enhanced the activity of p38 MAPK and the subsequent accumulation of cyclin-dependent kinase inhibitor p21, thus promoting G1/S arrest and monocyte/macrophage differentiation. Moreover, the decline of GCN5 acetyltransferase caused by p38IP downregulation was required but was not sufficient for monocyte/macrophage differentiation. This study demonstrated a new role for p38IP and a novel miR-200b-3p/p38IP pair in the regulation of monocyte/macrophage differentiation.

The p38-interacting protein (p38IP) regulates G2/M progression by promoting α-tubulin acetylation via inhibiting ubiquitination-induced degradation of the acetyltransferase GCN5.

p38-interacting protein (p38IP) is a component of the GCN5 histone acetyltransferase-containing coactivator complex (GCN5-SAGA complex). It remains unclear whether p38IP or GCN5-SAGA is involved in cell cycle regulation. Using RNA interference to knock down p38IP, we observed that cells were arrested at the G2/M phase, exhibiting accumulation of cyclins, shrunken spindles, and hypoacetylation of α-tubulin. Further analysis revealed that knockdown of p38IP led to proteasome-dependent degradation of GCN5. GCN5 associated with and acetylated α-tubulin, and recovering GCN5 protein levels in p38IP knockdown cells by ectopic expression of GCN5 efficiently reversed α-tubulin hypoacetylation and G2/M arrest. During the G2/M transition, the association of α-tubulin with GCN5 increased, and the acetylation of α-tubulin reached a peak. Biochemical analyses demonstrated that the interaction between p38IP and GCN5 depended on the p38IP N terminus (1-381 amino acids) and GCN5 histone acetyltransferase domain and bromodomain. The p38IP N terminus could effectively reverse p38IP depletion-induced GCN5 degradation, thus recovering α-tubulin acetylation and G2/M progression. p38IP-mediated suppression of GCN5 ubiquitination most likely occurs via nuclear sequestration of GCN5. Our data indicate that the GCN5-SAGA complex is required for G2/M progression, mainly because p38IP promotes the acetylation of α-tubulin by preventing the degradation of GCN5, in turn facilitating the formation of the mitotic spindle.