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

The Hedgehog (Hh) signaling pathway has critical functions during embryogen esis of both invertebrate and vertebrate species [1]; defects in this pathw ay in humans can cause developmental disorders as well as neoplasia [2], Al though the Gli1, Gli2, and Gli3 zinc finger proteins are known to be effect ers of Hh signaling in vertebrates, the mechanisms regulating activity of t hese transcription factors remain poorly understood [3,4]. In Drosophila, a ctivity of the Gli homolog Cubitus interruptus (Ci) is likely to be modulat ed by its interaction with a cytoplasmic complex containing several other p roteins [5,6], including Costal2, Fused (Fu), and Suppressor of fused (Su(f u)), 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 tra nscript 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 Glil, Gli2, and Gli3, and that the inhibitory effects of mSu(fu) on Gli1's transcriptional activ ity were mediated through interactions with both amino- and carboxy-termina l regions of Glil, Glil 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 Glil immunostaining, Our fin dings indicate that mSu(fu) can function as a negative regulator of Shh sig naling and suggest that this effect is mediated by interaction with Gli tra nscription factors.