Primary cilia regulate Gli/Hedgehog activation in pancreas.

Diabetes Center, Department of Medicine, University of California, San Francisco, CA 94143, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 06/2010; 107(22):10109-14. DOI: 10.1073/pnas.0909900107
Source: PubMed

ABSTRACT Previous studies have suggested that defects in pancreatic epithelium caused by activation of the Hedgehog (Hh) signaling pathway are secondary to changes in the differentiation state of the surrounding mesenchyme. However, recent results describe a role of the pathway in pancreatic epithelium, both during development and in adult tissue during neoplastic transformation. To determine the consequences of epithelial Hh activation during pancreas development, we employed a transgenic mouse model in which an activated version of GLI2, a transcriptional mediator of the pathway, is overexpressed specifically in the pancreatic epithelium. Surprisingly, efficient Hh activation was not observed in these transgenic mice, indicating the presence of physiological mechanisms within pancreas epithelium that prevent full Hh activation. Additional studies revealed that primary cilia regulate the level of Hh activation, and that ablation of these cellular organelles is sufficient to cause significant up-regulation of the Hh pathway in pancreata of mice overexpressing GLI2. As a consequence of overt Hh activation, we observe profound morphological changes in both the exocrine and endocrine pancreas. Increased Hh activity also induced the expansion of an undifferentiated cell population expressing progenitor markers. Thus, our findings suggest that Hh signaling plays a critical role in regulating pancreatic epithelial plasticity.


Available from: Matthias Hebrok, Mar 31, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Uncontrolled Hedgehog (Hh) signaling is the cause of several malignancies including the pediatric cancer medulloblastoma (MB), a neuroectodermal tumor affecting the cerebellum. Despite the development of potent Hh pathway antagonists, MB drug resistance is still an unresolved issue which requires the identification of novel drug targets. Following up on our observation that histone deacetylase 6 (HDAC6) expression was increased in Hh-driven MB, we found that this enzyme is essential for full Hh pathway activation. Intriguingly, these stimulatory effects of HDAC6 are partly integrated downstream of primary cilia, a known HDAC6-regulated structure. In addition, HDAC6 is also required for the complete repression of basal Hh target gene expression. These contrasting effects are mediated by HDAC6's impact on Gli2 mRNA and GLI3 protein expression. As a result of this complex interaction with Hh signaling, global transcriptome analysis revealed that HDAC6 regulates only a subset of Smoothened- and Gli-driven genes including all well-established Hh targets such as Ptch1 or Gli1. Importantly, MB cell survival was severely compromised by HDAC6 inhibition in vitro and pharmacological HDAC6 blockade strongly reduced tumor growth in an in vivo allograft model. In summary, our data describe an important role for HDAC6 in regulating the mammalian Hh pathway and encourage further studies focusing on HDAC6 as a novel drug target in MB. Copyright © 2014, American Association for Cancer Research.
    Molecular Cancer Therapeutics 12/2014; 14(3). DOI:10.1158/1535-7163.MCT-14-0481 · 5.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study, we focus our interest on some peculiar infrastructural abnormalities detected in a pancreatic cancer case. Our electron microscopic observations underline the high plasticity of the pancreatic parenchyma cells. Tumor pancreatic exocrine lesions are represented by putative ductal and acinar cells, which proliferate and grow in a haphazard pattern, detrimental to endocrine counterpart. The tumor cells do not exhibit neither a pure ductular or ductal nor a pure acinar phenotype, but tumor lesions represented by neoplastic ductal cells with invasive growth are by far prevalently. In our pancreatic cancer case, electron microscopic investigation clearly shows that a plethora of the epithelial cells from the tumor lesions contain large areas of autophagy leading to the pleomorphic inclusions represented by fibrillary/ filamentous inclusions frequently associated with hyaline-amorphous material, and secondary lysosomes. One of the mostly striking and important finding in this report for a case of pancreatic cancer is the high fragility (extensive dissolutions) of plasma membrane of tumor cells leading to pseudo-syncytia formation. Desmosomal junctions are severely altered, almost missing. Plasma membranes showed shedding membrane vesicles. Extravasated inflammatory cells contribute to the dramatic and extensive destructive areas of epithelial cells as well as tumor-stroma counterpart, including the basement membrane. All above severe infrastructural abnormalities, especially down regulation of cell-cell and cell-extracellular matrix adhesions might result in aberrant cell behavior and, consequently, much care should be taken for the postoperatory patient evolution.
    Romanian journal of morphology and embryology = Revue roumaine de morphologie et embryologie 03/2015; 2015(561):207-222. · 0.72 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Wnt signaling is a well conserved pathway critical for growth, patterning and differentiation of multiple tissues and organs. Previous studies on Wnt signaling in the pancreas have been based predominantly on downstream pathway effector genes such as β-catenin. We here provide evidence that the canonical-pathway member Wnt7b is a physiological regulator of pancreatic progenitor cell growth. Genetic deletion of Wnt7b in the developing pancreas leads to pancreatic hypoplasia due to reduced proliferation of pancreatic progenitor cells during the phase of pancreas development marked by rapid progenitor cell growth. While the differentiation potential of pancreatic progenitor cells is unaffected by Wnt7b deletion, through a gain-of-function analysis, we find that early pancreatic progenitor cells are highly sensitive to Wnt7b expression, but later lose such competence. By modulating the level and the temporal windows of Wnt7b expression we demonstrate a significant impact on organ growth and morphogenesis particularly during the early branching stages of the organ, which negatively affects generation of the pro-endocrine (Ngn3+/Nkx6.1+), and pro-acinar (Ptf1A+) fields. Consequently, Wnt7b gain-of-function results in failed morphogenesis and almost complete abrogation of the differentiation of endocrine and acinar cells, leading to cystic epithelial metaplasia expressing ductal markers including Sox9, Hnf6 and Hnf1β. While Wnt7b is expressed exclusively in the developing pancreatic epithelium, adjacent mesenchymal cells in the organ display a direct trophic response to elevated Wnt7b and increase expression of Lef1, cFos and desmin. Of note, in contrast to the pancreatic epithelium, the pancreatic mesenchyme remains competent to respond to Wnt7b ligand, at later stages in development. We conclude that Wnt7b helps coordinate pancreatic development through autocrine, as well as paracrine mechanisms, and as such represents a novel bi-modal morphogen ligand.
    Developmental Biology 01/2015; DOI:10.1016/j.ydbio.2014.12.031 · 3.64 Impact Factor