Physical and functional interactions between STAT3 and KAP1

Abstract

Signal transducers and activators of transcription (STATs) mediate cell proliferation, differentiation and survival in immune responses, hematopoiesis, neurogenesis and other biological processes. For example, STAT3 has been reported to be constitutively activated in numerous cancer cells. To clarify the molecular mechanisms underlying the STAT activation, we performed yeast two-hybrid screening and identified KAP1/TIF1b as a novel STATbinding partner. KAP1 is a universal corepressor protein for the Kruppel-associated box zinc-finger protein superfamily of transcriptional repressors. We found endogenous KAP1 associated with endogenous STAT3 in vivo. Importantly, small-interfering RNA-mediated reduction of KAP1 expression enhanced interleukin (IL)-6-induced STAT3-dependent transcription and gene expression. Furthermore, reduction of KAP1 expression resulted in the marked accumulation of STAT3 phosphorylated on Ser727 in the nucleus, a modification that regulates its transcriptional activation. These results indicate that KAP1 may serve as a transcriptional regulator of the IL-6/STAT3 signaling pathway.

KAP1 regulates type I interferon/STAT1-mediated IRF-1 gene expression

“…In our previous work, we have shown that KAP1 negatively regulates IFN-induced transcription by a transient reporter assay using the IFN-stimulated responsive element (ISRE)-LUC [12]. We further confirmed that KAP1 affects IFN-induced transcriptional activation and gene expression using siRNA to reduce the endogenous expression of KAP1 in HeLa cells.…”

“…Our previous study revealed that the C-terminal region of KAP1 (amino acids 394-835) interacts with ectopically expressed STAT1, STAT3, STAT4 or STAT6, but not with STAT2, STAT5a or STAT5b in 293T cells [12]. Here, we investigated whether wild-type STAT1 interacts with KAP1 and STAT1 phosphorylation state is involved in their interactions.…”

“…We recently identifed KAP1 [12], a co-repressor of the Kruppel-associated box (KRAB)-domain-containing zinc finger proteins [13][14][15] as a protein that interacts specifically with STAT1, STAT3, STAT4 and STAT6. KAP1 can recruit and coordinate many components involved in gene silencing.…”

Epstein–Barr virus-derived EBNA2 regulates STAT3 activation

“…The immunoprecipitates from cell lysates were resolved on SDS-PAGE and transferred to an Immobilon filter (Millipore; Bedford, MA), which was then immunoblotted with antibodies. To measure STAT3 DNA binding, cell extracts were treated with the immobilized STAT3 consensus oligonucleotide-Sepharose conjugate (Santa Cruz) as described previously [22].…”

The IL-6 family of cytokines modulates STAT3 activation by desumoylation of PML through SENP1 induction

“…Hep3B cells were treated with an siRNA-Lipofectamine 2000 (Invitrogen, Carlsbad, CA) mixture at 37 °C for 4 hrs, followed by addition of fresh medium containing 10% FCS as described previously [16].…”