Arhgap36-dependent activation of Gli transcription factors.

Hedgehog (Hh) pathway activation and Gli-dependent transcription play critical roles in embryonic patterning, tissue homeostasis, and tumorigenesis. By conducting a genome-scale cDNA overexpression screen, we have identified the Rho GAP family member Arhgap36 as a positive regulator of the Hh pathway in vitro and in vivo. Arhgap36 acts in a Smoothened (Smo)-independent manner to inhibit Gli repressor formation and to promote the activation of full-length Gli proteins. Arhgap36 concurrently induces the accumulation of Gli proteins in the primary cilium, and its ability to induce Gli-dependent transcription requires kinesin family member 3a and intraflagellar transport protein 88, proteins that are essential for ciliogenesis. Arhgap36 also functionally and biochemically interacts with Suppressor of Fused. Transcriptional profiling further reveals that Arhgap36 is overexpressed in murine medulloblastomas that acquire resistance to chemical Smo inhibitors and that ARHGAP36 isoforms capable of Gli activation are up-regulated in a subset of human medulloblastomas. Our findings reveal a new mechanism of Gli transcription factor activation and implicate ARHGAP36 dysregulation in the onset and/or progression of GLI-dependent cancers.

Small-molecule inhibitors reveal multiple strategies for Hedgehog pathway blockade.

Inappropriate activation of the Hedgehog (Hh) signaling pathway has been implicated in a diverse spectrum of cancers, and its pharmacological blockade has emerged as an anti-tumor strategy. While nearly all known Hh pathway antagonists target the transmembrane protein Smoothened (Smo), small molecules that suppress downstream effectors could more comprehensively remediate Hh pathway-dependent tumors. We report here four Hh pathway antagonists that are epistatic to the nucleocytoplasmic regulator Suppressor of Fused [Su(fu)], including two that can inhibit Hh target gene expression induced by overexpression of the Gli transcription factors. Each inhibitor has a unique mechanism of action, and their phenotypes reveal that Gli processing, Gli activation, and primary cilia formation are pharmacologically targetable. We further establish the ability of certain compounds to block the proliferation of cerebellar granule neuron precursors expressing an oncogenic form of Smo, and we demonstrate that Hh pathway inhibitors can have tissue-specific activities. These antagonists therefore constitute a valuable set of chemical tools for interrogating downstream Hh signaling mechanisms and for developing chemotherapies against Hh pathway-related cancers.

Bicyclic Imidazolium Inhibitors of Gli Transcription Factor Activity.

Gli transcription factors within the Hedgehog (Hh) signaling pathway direct key events in mammalian development and promote a number of human cancers. Current therapies for Gli-driven tumors target Smoothened (SMO), a G protein-coupled receptor-like protein that functions upstream in the Hh pathway. Although these drugs can have remarkable clinical efficacy, mutations in SMO and downstream Hh pathway components frequently lead to chemoresistance. In principle, therapies that act at the level of Gli proteins, through direct or indirect mechanisms, would be more efficacious. We therefore screened 325 120 compounds for their ability to block the constitutive Gli activity induced by loss of Suppressor of Fused (SUFU), a scaffolding protein that directly inhibits Gli function. Our studies reveal a family of bicyclic imidazolium derivatives that can inhibit Gli-dependent transcription without affecting the ciliary trafficking or proteolytic processing of these transcription factors. We anticipate that these chemical antagonists will be valuable tools for investigating the mechanisms of Gli regulation and developing new strategies for targeting Gli-driven cancers.

HIPK4 is essential for murine spermiogenesis.

Mammalian spermiogenesis is a remarkable cellular transformation, during which round spermatids elongate into chromatin-condensed spermatozoa. The signaling pathways that coordinate this process are not well understood, and we demonstrate here that homeodomain-interacting protein kinase 4 (HIPK4) is essential for spermiogenesis and male fertility in mice. HIPK4 is predominantly expressed in round and early elongating spermatids, and Hipk4 knockout males are sterile, exhibiting phenotypes consistent with oligoasthenoteratozoospermia. Hipk4 mutant sperm have reduced oocyte binding and are incompetent for in vitro fertilization, but they can still produce viable offspring via intracytoplasmic sperm injection. Optical and electron microscopy of HIPK4-null male germ cells reveals defects in the filamentous actin (F-actin)-scaffolded acroplaxome during spermatid elongation and abnormal head morphologies in mature spermatozoa. We further observe that HIPK4 overexpression induces branched F-actin structures in cultured fibroblasts and that HIPK4 deficiency alters the subcellular distribution of an F-actin capping protein in the testis, supporting a role for this kinase in cytoskeleton remodeling. Our findings establish HIPK4 as an essential regulator of sperm head shaping and potential target for male contraception.

The imidazopyridine derivative JK184 reveals dual roles for microtubules in Hedgehog signaling.

Eradicating hedgehogs: The title molecule has been previously identified as a potent inhibitor of the Hedgehog signaling pathway, which gives embryonic cells information needed to develop properly. This molecule is shown to modulate Hedgehog target gene expression by depolymerizing microtubules, thus revealing dual roles of the cytoskeleton in pathway regulation (see figure).

Axiom Microbiome Array, the next generation microarray for high-throughput pathogen and microbiome analysis.

Microarrays have proven to be useful in rapid detection of many viruses and bacteria. Pathogen detection microarrays have been used to diagnose viral and bacterial infections in clinical samples and to evaluate the safety of biological drug materials. In this study, the Axiom Microbiome Array was evaluated to determine its sensitivity, specificity and utility in microbiome analysis of veterinary clinical samples. The array contains probes designed to detect more than 12,000 species of viruses, bacteria, fungi, protozoa and archaea, yielding the most comprehensive microbial detection platform built to date. The array was able to detect Shigella and Aspergillus at 100 genome copies, and vaccinia virus DNA at 1,000 genome copies. The Axiom Microbiome Array made correct species-level calls in mock microbial community samples. When tested against serum, tissue, and fecal samples from pigs experimentally co-infected with porcine reproductive and respiratory syndrome virus and porcine circovirus type 2, the microarray correctly detected these two viruses and other common viral and bacterial microbiome species. This cost-effective and high-throughput microarray is an efficient tool to rapidly analyze large numbers of clinical and environmental samples for the presence of multiple viral and bacterial pathogens.

In vivo imaging of Hedgehog pathway activation with a nuclear fluorescent reporter.

The Hedgehog (Hh) pathway is essential for embryonic development and tissue regeneration, and its dysregulation can lead to birth defects and tumorigenesis. Understanding how this signaling mechanism contributes to these processes would benefit from an ability to visualize Hedgehog pathway activity in live organisms, in real time, and with single-cell resolution. We report here the generation of transgenic zebrafish lines that express nuclear-localized mCherry fluorescent protein in a Gli transcription factor-dependent manner. As demonstrated by chemical and genetic perturbations, these lines faithfully report Hedgehog pathway state in individual cells and with high detection sensitivity. They will be valuable tools for studying dynamic Gli-dependent processes in vertebrates and for identifying new chemical and genetic regulators of the Hh pathway.

Oncogenic transformation of diverse gastrointestinal tissues in primary organoid culture.

The application of primary organoid cultures containing epithelial and mesenchymal elements to cancer modeling holds promise for combining the accurate multilineage differentiation and physiology of in vivo systems with the facile in vitro manipulation of transformed cell lines. Here we used a single air-liquid interface culture method without modification to engineer oncogenic mutations into primary epithelial and mesenchymal organoids from mouse colon, stomach and pancreas. Pancreatic and gastric organoids exhibited dysplasia as a result of expression of Kras carrying the G12D mutation (Kras(G12D)), p53 loss or both and readily generated adenocarcinoma after in vivo transplantation. In contrast, primary colon organoids required combinatorial Apc, p53, Kras(G12D) and Smad4 mutations for progressive transformation to invasive adenocarcinoma-like histology in vitro and tumorigenicity in vivo, recapitulating multi-hit models of colorectal cancer (CRC), as compared to the more promiscuous transformation of small intestinal organoids. Colon organoid culture functionally validated the microRNA miR-483 as a dominant driver oncogene at the IGF2 (insulin-like growth factor-2) 11p15.5 CRC amplicon, inducing dysplasia in vitro and tumorigenicity in vivo. These studies demonstrate the general utility of a highly tractable primary organoid system for cancer modeling and driver oncogene validation in diverse gastrointestinal tissues.