The role of Suppressor of Fused in the regulation of Hedgehog and Wnt/ß-Catenin signaling pathway in adult liver

Aims: Sufu is one of the most important regulatory elements that can negatively influence the Hedgehog signaling pathway, witch plays a critical role in cell differentiation and development of the liver. In the absence of Hedgehog signals, Sufu forms an inhibition complex with Fu and Cos2, causing a proteolytic cleavage of the transcription factors Gli2 and Gli3 into their repressor forms and so inhibiting the expression of the target genes(1). Sufu can also directly interact with the Gli1 protein on the DNA, thus, suppressing Gli1 transcriptional activity in the nucleus (2). Further, Sufu can play a role in the Wnt/ß-Catenin signaling cascades by binding to the protein ß-Catenin repressing the TCF- mediated transcription (3). Wnt/ß-Catenin signaling plays a role in balancing hepatic metabolism via acting as a master regulator of liver zonation (4). Therefore, we wanted to study the influence of Sufu by RNA interference in adult hepatocytes. Methods: A siRNA-mediated knockdown of Sufu was performed in cultured mouse hepatocytes for 48h. Alterations in gene expression of components of the Hedgehog and Wnt/ß-Catenin pathways were determined by quantitative RT-PCR. Results: Knockdown of Sufu expression stimulated Hedgehog signaling and significantly increased mRNA levels of Gli1, –2 and –3 as well as of the Hedgehog ligands Indian and Sonic hedgehog, and some downstream target genes (PPAR-a, GATA–4, SREBP1). Likewise, components of the Wnt/ß-Catenin pathway responded by reducing the expression of APC, Axin2, GSK3ß and, less pronounced, even ß-Catenin. Interestingly, also the Wnt/ß-Catenin target genes cMyc and CyclinD decreased, although the reduction of APC, Axin2, and GSK3ß may suggest an activation of this pathway. Conclusion: Sufu is active in adult mouse hepatocytes and seems to play an important role in coordinating morphogen signaling through the Wnt/ß-Catenin and the Hedgehog pathway.

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