The p38-interacting protein p38IP suppresses TCR and LPS signaling by targeting TAK1 (2020)
Figure 3

Figure 3. p38IP competes with TABs for binding to TAK1, interrupting K63-linked polyUb chain transfer from TAB2 to TAK1

(A) Fragmentation spectrum of the p38IP peptide identified in TAK1 complex immunoprecipitated from Jurkat TAg cells by liquid chromatography-tandem mass spectrometry. m/z, mass/charge ratio.

(B) HEK293T cells were transfected with YFP-p38IP, and the cell lysates aliquots were immunoprecipitated with IgG, anti-TAB1, anti-TAB2 and anti-TAK1 respectively, and then immunoblotted with the indicated antibodies.

(C) sh-NC or sh-p38IP Jurkat E6.1 T cells were stimulated with 10 μg/ml anti-CD3 plus 2 μg/ml anti-CD28 for the indicated times and lysed, followed byTAK1 immunoprecipitation. TAK1 beads were washed three times with lysis buffer and two times with kinase buffer, then resuspended in kinase buffer containing 100 μM ATP and 1μg recombinant GST-IKKβ(111-250aa) protein as substrate to perform in vitro kinase assay, and then immunoblot analysis with p-IKKβ antibody.

(D) HEK293T cells were transfected with cMyc vector ( - ) or increasing amounts of cMyc-p38IP (wedge), and 24 hours post transfection, the cell lysates were immunoprecipitated with IgG or anti-TAB2 and then immunoblotted with anti-TAK1 and anti-TAB2. Expression of cMyc-p38IP was determined in the immunoblotted lysates with anti-cMyc.

(E) HEK293T cells were transfected with HA vector ( - ) or increasing amount of HA-p38IP (wedge), and 24 hours post transfection, the cell lysates were immunoprecipitated with IgG or anti-TAK1 and then immunoblotted with anti-TAB2, anti-TAB1, anti-HA and anti-TAK1. Expression of HA-p38IP was determined in the immunoblotted lysates with anti-HA.

(F) sh-NC and sh-p38IP Jurkat E6.1 T cells were stimulated with 10 μg/ml anti-CD3 plus 2 μg/ml anti-CD28 for the indicated times, and the cell lysates were immunoprecipitated with anti-TAB2 and immunoblotted with anti-TAK1 and anti-TAB2.

(G) Schematic showing the balance between TAK1-p38IP and TAK1-TABs complexes in resting cells.

(H) Jurkat TAg T cells transfected with cMyc vector or cMyc-p38IP were stimulated with 10μg/ml anti-CD3 for the indicated times, and then were lysed and immunoprecipitated with anti-TAK1 antibody and immunoblotted with anti-K63Ub, anti-cMyc and anti-TAK1 antibodies. Lysates were blotted with the indicated antibodies, and actin served as the loading control.

(I) sh-NC and sh-p38IP Jurkat E6.1 T cells stimulated as in (F) were lysed and immunoprecipitated with anti-TAK1 and immunoblotted with anti-K63Ub and anti-TAK1. Lysates were immunoblotted with the indicated antibodies.

(J) Jurkat TAg T cells transfected and stimulated as in (H) were lysed and immunoprecipitated with anti-TAB2 and immunoblotted with anti-K63Ub and anti-TAB2.

(K) sh-NC and sh-p38IP Jurkat E6.1 cells stimulated as in (F) were lysed and immunoprecipitated with anti-TAB2 and immunoblotted with anti-K63Ub and anti-TAB2. Data (B-F, H-K) are representatives of at least three independent experiments.

(L) Schematic showing that p38IP blocks the delivery of unanchored polyUb chains from TAB2 to TAK1.