SNIP1 Inhibits NF-κB Signaling by Competing for Its Binding to the C/H1 Domain of CBP/p300 Transcriptional Co-activators

Abstract

SNIP1 is a 396-amino acid nuclear protein shown to be an inhibitor of the TGF-␤ signal transduction pathway and to be important in suppressing transcriptional activation dependent on the co-activators CBP and p300. In this report we show that SNIP1 potently inhibits the activity of NF-B, which binds the C/H1 domain of CBP/ p300, but does not interfere with the activity of transcription factors such as p53, which bind to other domains of p300, or factors such as VP16, which are independent of these co-activators. Inhibition of NF-B activity is a function of the N-terminal domain of SNIP1 and involves competition of SNIP1 and the NF-B subunit, RelA/p65, for binding to p300, similar to the mechanism of inhibition of Smad signaling by SNIP1. Immunohistochemical staining shows that expression of SNIP1 is strictly regulated in development and that it colocalizes, in certain tissues, with nuclear staining for RelA/p65 and for p300, suggesting that they may regulate NF-B activity in vivo in a spatially and temporally controlled manner. These data led us to suggest that SNIP1 may be an inhibitor of multiple transcriptional pathways that require the C/H1 domain of CBP/p300.

The FHA domain protein SNIP1 is a regulator of the cell cycle and cyclin D1 expression

“…Together, these results demonstrate that SNIP1 is an important cellular regulator of cell proliferation and the cell cycle, functionally linked to known oncogenes. SNIP1 had previously been identified as a p300 coactivator interacting protein (Kim et al, 2000(Kim et al, , 2001 and our studies were originally initiated to further investigate the functional significance of this observation. Although we verified the interaction of SNIP1 with p300 in NMuMg cells, we did not observe this interaction in the U-2 OS cells used in many of our experiments (Figure 4).…”

“…Subsequent studies revealed that SNIP1 also interacts with the C/H1 domain of the transcriptional coactivators p300 and CREB binding protein (CBP) (Kim et al, 2000), which functions as a binding site for many transcriptional regulators (Goodman and Smolik, 2000). Through this interaction, SNIP1 overexpression was shown to inhibit the activity of the RelA(p65) nuclear factor-kB (NF-kB) subunit and displace binding of Smad4 to this domain (Kim et al, 2000(Kim et al, , 2001. Therefore, SNIP1 has the potential to function as a regulator of many transcription factors.…”

Regulation of ATR-dependent pathways by the FHA domain containing protein SNIP1

“…Interestingly, transfection of HAtagged SNIP1 deletion mutants revealed that the interaction was specific for the FHA-domain containing C-terminal region of SNIP1 (Figure 5b). By comparison, it is the N-terminal region of SNIP1 that has been previously shown to interact with the p300 coactivator and bind RelA in vitro (Kim et al, 2000(Kim et al, , 2001. Importantly, gel filtration analysis demonstrated that neither ATR nor Chk1 is present in the high-molecularweight SNIP1 complex we identified previously (Roche et al, 2004) (Figure 5c), suggesting that this interaction is weak and likely to be transient.…”

“…SNIP1 has previously been implicated as a regulator of NF-kB through binding p300 (Kim et al, 2001). SNIP1 has also been reported to bind directly to the Rel homology domain (RHD) of RelA (Kim et al, 2001).…”

“…Subsequent studies have also demonstrated potential interactions with the p300 coactivator proteins and BRG1, a component of the ATP-dependent chromatin remodelling complex, Swi/Snf (Kim et al, 2000(Kim et al, , 2001Roche et al, 2004). In the case of p300, this interaction appears to be cell-type-specific, suggesting that the ability of SNIP1 to interact with multiple transcriptional regulators may be regulated by posttranslational modification (Roche et al, 2004).…”