TGF-β signalling is regulated by Schnurri-2-dependent nuclear translocation of CLIC4 and consequent stabilization of phospho-Smad2 and 3

Abstract

CLIC4, a multifunctional protein that traffics between the cytoplasm and nucleus, interacts with Schnurri-2, a transcription factor in the BMP pathway. TGF-β enhances the expression of both CLIC4 and Schnurri-2 and promotes their association in the cytoplasm and their translocation to the nucleus. In the absence of CLIC4 or Schnurri-2, TGF-β signalling is abrogated. Direct nuclear targeting of CLIC4 enhances TGF-β signalling and removes the requirement for Schnurri-2. Nuclear CLIC4 associates with phospho-Smad2 and 3 and protects them from dephosphorylation by nuclear phosphatases. An intact TGF-β signalling pathway is essential for CLIC4 to mediate growth arrest. These results reveal Schnurri-2 and CLIC4 as previously unidentified modifiers of TGF-β signalling through stabilizing phospho-Smad2 and phospho-Smad3 in the nucleus.

Genome-wide Repression of NF-κB Target Genes by Transcription Factor MIBP1 and Its Modulation by O-Linked β-N-Acetylglucosamine (O-GlcNAc) Transferase

“…The knockdown experiments also showed that the expression of many of the TGF-␤ signaling pathway members was decreased by lowered levels of MIBP1 (Table 4). These results are consistent with a recent report of CLIC4⅐MIBP1 complex formation and the subsequent nuclear translocation of CLIC4, leading to activation of the TGF-␤ signaling pathway by MIBP1 (48). However, these observations are contrary to the results of our array experiments in which gene sets of TGF-␤ pathways were down-regulated when MIBP1 was stably overexpressed.…”

Inducible NOS-induced chloride intracellular channel 4 (CLIC4) nuclear translocation regulates macrophage deactivation

“…CLIC4 nuclear translocation is regulated by NOS activity through direct modification of a CLIC4 cysteine residue by NO (13), and nuclear CLIC4 functions to enhance TGF-β signaling (8), the latter being a critical modulator of macrophage deactivation (17). Stimulation with LPS and IFNγ induces Snitrosylation of CLIC4 in macrophages as detected by a biotin switch assay (Fig.…”

“…The Smad-dependent TGF-β1 pathway, specifically Smad3, is essential for abatement of the proinflammatory macrophage phenotype, including iNOS and IL-1β (27,28), whereas Smad4 is important for endotoxin tolerance (29). We have previously established that nuclear CLIC4 is an essential positive modulator of TGF-β1 signaling in keratinocytes through its stabilization of phosphoSmad2/3 by disrupting their interaction with the phosphatase PPM1A (8). Thus, it is likely that the prolonged proinflammatory phenotype of CLIC4 knockout macrophages stems from aberrant TGF-β1 signaling.…”

“…Although the chloride-selective channel activity of various members has long been established by multiple groups (1)(2)(3), the signaling and adaptor functions of soluble CLIC4 and other members have only recently come to the fore. Soluble CLIC4, originally identified as a p53-and c-myc-responsive proapoptotic protein (4,5), is important for PKCdependent keratinocyte differentiation (6) and a modulator of TGFβ signaling in multiple cell types (7)(8)(9). Many of these proapoptotic and differentiation functions of CLIC4 are dependent on its translocation to the nucleus (6,8,10).…”

“…Soluble CLIC4, originally identified as a p53-and c-myc-responsive proapoptotic protein (4,5), is important for PKCdependent keratinocyte differentiation (6) and a modulator of TGFβ signaling in multiple cell types (7)(8)(9). Many of these proapoptotic and differentiation functions of CLIC4 are dependent on its translocation to the nucleus (6,8,10). CLIC4 exhibits redox sensitivity in both its soluble and membrane-associated states (11,12).…”