Mouse Suppressor of fused is a negative regulator of Sonic hedgehog signaling and alters the subcellular distribution of Gli1

Abstract

The Hedgehog (Hh) signaling pathway has critical functions during embryogenesis of both invertebrate and vertebrate species [1]; defects in this pathway in humans can cause developmental disorders as well as neoplasia [2]. Although the Gli1, Gli2, and Gli3 zinc finger proteins are known to be effectors of Hh signaling in vertebrates, the mechanisms regulating activity of these transcription factors remain poorly understood [3] [4]. In Drosophila, activity of the Gli homolog Cubitus interruptus (Ci) is likely to be modulated by its interaction with a cytoplasmic complex containing several other proteins [5] [6], including Costal2, Fused (Fu), and Suppressor of fused (Su(fu)), the last of which has been shown to interact directly with Ci [7]. We have cloned mouse Suppressor of fused (mSu(fu)) and detected its 4.5 kb transcript throughout embryogenesis and in several adult tissues. In cultured cells, mSu(fu) overexpression inhibited transcriptional activation mediated by Sonic hedgehog (Shh), Gli1 and Gli2. Co-immunoprecipitation of epitope-tagged proteins indicated that mSu(fu) interacts with Gli1, Gli2, and Gli3, and that the inhibitory effects of mSu(fu) on Gli1's transcriptional activity were mediated through interactions with both amino- and carboxy-terminal regions of Gli1. Gli1 was localized primarily to the nucleus of both HeLa cells and the Shh-responsive cell line MNS-70; co-expression with mSu(fu) resulted in a striking increase in cytoplasmic Gli1 immunostaining. Our findings indicate that mSu(fu) can function as a negative regulator of Shh signaling and suggest that this effect is mediated by interaction with Gli transcription factors.

Hedgehog signaling overrides p53-mediated tumor suppression by activating Mdm2

“…Gli1 and Gli2 expression was determined by immunoblotting, using antibodies against each tag. ( f) p53 and SMO-M2 expression plasmids were transfected into C3H10T1/2 cells with or without the Myc-tagged SuFu expression plasmid (40). Forty-eight hours after transfection, the amount of p53 protein was determined by immunoblotting.…”

Regulation of Hedgehog signaling: a complex story

“…Studies involving mammalian Su(fu) support this hypothesis. Over-expression of human SU(FU) in cultured mammalian cells triggers increased cytoplasmic GLI-1 and decreased expression of Gli reporter construct(s) [88][89][90].…”

Failure of a medulloblastoma-derived mutant of SUFU to suppress WNT signaling

“…Tumors from these children showed loss of heterozygosity, implying that SUFU is a bona fide tumor suppressor gene, and that germline mutation of SUFU is a novel mechanism predisposing to MB. SUFU is a known inhibitor of the Sonic Hedgehog (SHH) signaling cascade; it is thought to repress SHH signaling by exporting the effectors of SHH signaling, the Gli family of transcription factors from the nucleus to the cytoplasm where they are inactive (Ding et al, 1999;Pearse et al, 1999;Methot and Basler, 2000;Murone et al, 2000). An MB-derived truncated mutant of SUFU was shown to have lost its association with Gli1, and lost the ability to export Gli1 from the nucleus and therefore repress SHH signaling (Taylor et al, 2002).…”