Background/Aims: The Hippo signaling pathway regulates expansion and differentiation of stem cells and tissue progenitor cells during organ development and tissue regeneration. Previous studies have shown that YAP1, a potent effector of the Hippo signaling pathway, plays a crucial role in pancreas development, but the function of YAP1 in pancreatic progenitor cells is less known. Methods: The spatio-temporal expression pattern of YAP1 in mouse developing pancreata was detected by in situ hybridization. The effect of silencing YAP1 on the proliferation of pancreatic progenitor cells was analyzed by CCK-8 assay and Ki67 immunostaining. The regulation of miR-375 on YAP1 expression was determined by dual luciferase reporter assay, QRT-PCR and western blot. Finally, the influence of miR-375 on proliferation of pancreatic progenitor cells was analyzed by CCK-8 assay and Ki67 immunostaining. Results: We found that YAP1 was highly expressed in embryonic and adult pancreatic progenitor cells. Knocking down YAP1 by siRNA inhibited the proliferation of pancreatic progenitor cells. The mouse YAP1 was a target gene of miR-375, and miR-375 could target the 3' UTR of YAP1 mRNA to decrease its protein and mRNA levels. Similar to silencing YAP1 by siRNA, the proliferation of pancreatic progenitor cells was inhibited significantly by miR-375. Conclusion: Our results indicate that YAP1 is necessary for the proliferation of pancreatic progenitor cells and miR-375 participates in regulating YAP1 expression during pancreatic progenitor cells differentiation.
Cell behaviors, including proliferation, differentiation and apoptosis, are intricately controlled during organ development and tissue regeneration. In the past 9 years, the Hippo signaling pathway has been delineated to play critical roles in organ size control, tissue regeneration and tumorigenesis through regulating cell behaviors. In mammals, the core modules of the Hippo signaling pathway include the MST1/2-LATS1/2 kinase cascade and the transcriptional co-activators YAP/TAZ. The activity of YAP/TAZ is suppressed by cytoplasmic retention due to phosphorylation in the canonical MST1/2-LATS1/2 kinase cascade-dependent manner or the non-canonical MST1/2- and/or LATS1/2-independent manner. Hippo signaling pathway, which can be activated or inactivated by cell polarity, contact inhibition, mechanical stretch and extracellular factors, has been demonstrated to be involved in development and tumorigenesis of liver and pancreas. In addition, we have summarized several small molecules currently available that can target Hippo-YAP pathway for potential treatment of hepatic and pancreatic cancers, providing clues for other YAP initiated cancers therapy as well.
Mesenchymal stem cells (MSCs) are pluripotent cells which can differentiate into several distinct lineages, such as chondrocytes, adipocytes and myofibers. It has been reported that the lineage-specific transcriptional factors including Runt related transcription factor 2 (RUNX2), Peroxisome proliferator-activator receptor gamma (PPARgamma) and Myogenic differentiation 1 (MyoD) may play key regulatory roles among the differentiation of MSCs. Recently, researches have confirmed that the Hippo pathway impacts the differentiation fates of MSCs through regulating the activity of line- age-specific transcription factors by the Hippo pathway effectors Tafazzin (TAZ) and/or Yes-associated protein (YAP). The interaction between TAZ and RUNX2 boosts the osteogenic processes and promotes MSCs differentiating into osteoblast lineage. However, PPARgamma binding to TAZ may inhibit the adipocytes differentiation, and thus overexpression of TAZ in mesenchymal stem cell-like cells increases the expression of myogenic genes and hastens myofiber formation through a MyoD-dependent manner. Moreover, other signaling pathways (such as BMP-2, TNF-alpha, Eph-Ephrin, etc.), small molecules (KR62980, TM-25659, etc.), and mechanistic stimuli can also affect the fate by regulating the activity of TAZ/YAP. In this review, we summarized the signaling pattern of Hippo pathway and the function mechanism of TAZ and/or YAP by enumerating their interaction to several lineage-specific transcriptional factors and relationship with other signal pathways during MSCs differentiation.
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