Fig 2: The Cell Signaling no. 3037 anti-P-p65 Ser276-immunoreactive band persists in cells where p65 is silenced via an siRNA approach. 1321N1 cells were transiently transfected with control or p65 siRNA as described in Section 2. Cells were induced for 90 min with TNF-α (2000 IU/mL), iso (10 μM), or a combination of both stimuli. Presence of Ser276-phosphorylated p65 in cell lysates was analysed by Western Blot using Cell Signaling no. 3037 (A1). 130 and 80 kDa immunoreactivities are indicated by arrows. Western Blot to detect anti-P-p65Ser536 (65 kDa arrow) was performed on the same lysates (B1). Blots A1 and B1 were extensively washed and reprobed with anti-p65 to investigate efficiency of p65 knock-down. Anti-p65 detected bands are marked with arrows (A2, B2). Finally, blots were reprobed with anti-tubulin to check loading efficiency. Anti-tubulin-detected bands are marked with arrows (A3, B3).

Fig 3: In vitro recognition of the phosphorylated Serine 276 residue of p65 by Cell Signaling no. 3037. Recombinant wt p65-GST or SC mutant p65-GST fusion proteins were in vitro phosphorylated using recombinant MSK-1. 250 ng of the recombinant proteins were spotted on a nitrocellulose membrane and subjected to Western Blotting with Ser276 phospho-specific p65 antibody, either preincubated with 10 μg/mL phosphorylated peptide that was used to generate the antibody (upper panel) or not. 1 μg of recombinant protein was separated by SDS-PAGE after the in vitro kinase assays performed either in the presence of active MSK-1 and/or 10 μM H89 (lower panel) or not.

Fig 4: Four independent anti-P-p65 Ser276 antibodies detect inducible bands, with MWs of 80 and 130 kDa, that do not disappear upon p65 knock-down, but are inhibited when PKAcα is silenced. 1321N1 cells were transiently transfected with control, p65 or PKAcα siRNA, as described in Section 2. Cells were induced for 90 min with TNF-α (2000 IU/mL), iso (10 μM) or a combination of both stimuli. Presence of Ser276-phosphorylated p65 in cell lysates was analysed by Western Blot using SAB no. 11011 (A1), Rockland no. 100-401-264 (B1), Cell Signaling no. 3037 (B3), or a homemade anti-P-p65 Ser276 antibody (C1). 130 and 80 kDa immunoreactivities are indicated by arrows (1 and 2, resp.). Blots were extensively washed and reprobed with a mixture of anti-p65 and anti-PKAcα to investigate knock-down efficiency. Anti-p65-detected bands are marked by the upper arrow, anti-PKAcα-reactive bands are marked by the lower arrow (A2, B2, C2). Tubulin loading controls are added as Supplementary Figure 1.

Fig 5: Anti-phospho-p65 Ser276 (Cell Signaling no. 3037) detects atypical (with MWs of 80 and 130 kDa), inducible immunoreactivities in different cell types, induced with different NF-κB-activating agents. Cells were stimulated for increasing times (L929sA, A549, L363) or for 30 min (Raw264.7, C2C12, 1321N1) with TNF-α (2000 IU/mL), LPS (1 μg/mL), PMA (10 ng/mL), forskolin (forsk, 10 μM) or isoproterenol (iso, 10 μM). For blocking experiments, lysates were loaded on one gel in duplicate and after transfer, blots were cut in half. Immunodetection was performed in parallel, using Cell Signaling no. 3037 or Cell Signaling no. 3037 preincubated for at least 30 minutes with double volume of blocking peptide (BLOCK). Arrow 1 indicates an immunoreactive band with an MW of 130 kDa; arrow 2 indicates an immunoreactive band of 80 kDa.