Large tumor suppressor homologs 1 and 2 regulate mouse liver progenitor cell proliferation and maturation through antagonism of the coactivators YAP and TAZ.

In the adult liver, the Hippo pathway mammalian STE20-like protein kinases 1 and 2 and large tumor suppressor homologs 1 and 2 (LATS1/2) control activation of the transcriptional coactivators Yes-associated protein (YAP) and WW domain containing transcription regulator 1 (TAZ) in hepatocytes and biliary epithelial cells, thereby regulating liver cell proliferation, differentiation, and malignant transformation. Less is known about the contribution of Hippo signaling to liver development. We used conditional mutagenesis to show that the Hippo signaling pathway kinases LATS1 and LATS2 are redundantly required during mouse liver development to repress YAP and TAZ in both the biliary epithelial and hepatocyte lineages. In the absence of LATS1/2, biliary epithelial cells exhibit excess proliferation while hepatoblasts fail to mature into hepatocytes, defects that result in perinatal lethality. Using an in vitro hepatocyte differentiation assay, we demonstrate that YAP activity decreases and Hippo pathway kinase activities increase upon differentiation. In addition, we show that YAP activation in vitro, resulting from either depletion of its negative regulators LATS1/2 or expression of a mutant form of YAP that is less efficiently phosphorylated by LATS1/2, results in transcriptional suppression of genes that normally accompany hepatocyte maturation. Moreover, we provide evidence that YAP activity is repressed by Hippo pathway activation upon hepatocytic maturation in vitro. Finally, we examine the localization of YAP during fetal liver development and show that higher levels of YAP are found in biliary epithelial cells, while in hepatocytes YAP levels decrease with hepatocyte maturation. Hippo signaling, mediated by the LATS1 and LATS2 kinases, is required to restrict YAP and TAZ activation during both biliary and hepatocyte differentiation. These findings suggest that dynamic regulation of the Hippo signaling pathway plays an important role in differentiation and functional maturation of the liver. (Hepatology 2016;64:1757-1772).

Yi J ，Lu L ，Yanger K ，Wang W ，Sohn BH ，Stanger BZ ，Zhang M ，Martin JF ，Ajani JA ，Chen J ，Lee JS ，Song S ，Johnson RL ... -  《-》

Lats1/2 Regulate Yap/Taz to Control Nephron Progenitor Epithelialization and Inhibit Myofibroblast Formation.

In the kidney, formation of the functional filtration units, the nephrons, is essential for postnatal life. During development, mesenchymal progenitors tightly regulate the balance between self-renewal and differentiation to give rise to all nephron epithelia. Here, we investigated the functions of the Hippo pathway serine/threonine-protein kinases Lats1 and Lats2, which phosphorylate and inhibit the transcriptional coactivators Yap and Taz, in nephron progenitor cells. Genetic deletion of Lats1 and Lats2 in nephron progenitors of mice led to disruption of nephrogenesis, with an accumulation of spindle-shaped cells in both cortical and medullary regions of the kidney. Lineage-tracing experiments revealed that the cells that accumulated in the interstitium derived from nephron progenitor cells and expressed E-cadherin as well as vimentin, a myofibroblastic marker not usually detected after mesenchymal-to-epithelial transition. The accumulation of these interstitial cells associated with collagen deposition and ectopic expression of the myofibroblastic markers vimentin and α-smooth-muscle actin in developing kidneys. Although these myofibroblastic cells had high Yap and Taz accumulation in the nucleus concomitant with a loss of phosphorylated Yap, reduction of Yap and/or Taz expression levels completely rescued the Lats1/2 phenotype. Taken together, our results demonstrate that Lats1/2 kinases restrict Yap/Taz activities to promote nephron progenitor cell differentiation in the mammalian kidney. Notably, our data also show that myofibroblastic cells can differentiate from nephron progenitors.

McNeill H ，Reginensi A 《-》

LATS-YAP/TAZ controls lineage specification by regulating TGFβ signaling and Hnf4α expression during liver development.

Lee DH ，Park JO ，Kim TS ，Kim SK ，Kim TH ，Kim MC ，Park GS ，Kim JH ，Kuninaka S ，Olson EN ，Saya H ，Kim SY ，Lee H ，Lim DS ... -  《Nature Communications》

An evolutionarily conserved negative feedback mechanism in the Hippo pathway reflects functional difference between LATS1 and LATS2.

Park GS ，Oh H ，Kim M ，Kim T ，Johnson RL ，Irvine KD ，Lim DS ... -  《Oncotarget》

Sphingosylphosphorylcholine regulates the Hippo signaling pathway in a dual manner.

Sphingosylphosphorylcholine (SPC) is a bioactive sphingolipid which regulates many cancer-related processes, including cellular proliferation. The Hippo signaling pathway consists of a cascade of tumor suppressive kinases Mst1/2 and Lats1/2 and their downstream targets YAP and TAZ which are generally pro-proliferative transcriptional regulators. Direct phosphorylation by Lats1/2 causes inhibition or degradation of YAP/TAZ and down-regulation of their target genes. We found SPC treatment of MDA-MB-435S breast cancer cells to strongly inhibit their proliferation and to induce a sustained Lats2 protein expression (6-24h). Therefore, we hypothesized that Hippo signaling might mediate the anti-proliferative SPC response. We also saw a cell density-dependent increase in S127-phosphorylated YAP (pS127-YAP) and a decrease in mRNA levels of YAP target genes (CTGF, Cyr61) in response to long (9h) SPC treatment. Knockdown of S1P receptor 2 (S1P2) prevented the SPC-induced up-regulation of Lats2 and attenuated the anti-proliferative effect of SPC. However, while knockdown of Lats2 alone or in combination with Lats1 expectedly increased basal proliferation it did not attenuate the SPC-induced inhibition of proliferation. Exogenous expression of wild-type or kinase-dead Lats2 and knockdown of YAP/TAZ also had no effect on the anti-proliferative SPC response. It has been previously shown that activation of S1P2-G12/13 by sphingosine-1-phosphate (S1P) leads to rapid de-phosphorylation and up-regulation of YAP. Similarly, we saw a decrease in pS127-YAP and an increase in total YAP levels with short (1h) SPC treatment as well as a subsequent transient increase in YAP target gene expression. Inhibition of S1P2 prevented the SPC-induced YAP de-phosphorylation. The rapid YAP activation and subsequent up-regulation of Lats2 mRNA does not constitute a negative feedback loop as knockdown of YAP/TAZ did not inhibit SPC-induced Lats2 expression. In conclusion, in this study we show that SPC is able to regulate Hippo signaling in a dual and opposite manner, causing an initial activation of YAP followed by an inhibition. However, even the strong SPC-induced effects seen in Lats2 and YAP did not mediate the anti-proliferative SPC response.

Kemppainen K ，Wentus N ，Lassila T ，Laiho A ，Törnquist K ... -  《-》