Dr. Anthony E. Oro and colleagues (Stanford University) have identified two key Gli protein degradation signals that directly affect tumor latency in a mouse model of human skin cancer.

Their paper has been made available online ahead of print and will appear on the cover of the February 1 issue of the scientific journal Genes & Development.

Gli proteins are transcriptional mediators of the Sonic Hedgehog intracellular signaling pathway. Aberrant Shh signaling is implicated in a variety of human birth defects and about 25% of human tumors. Dr. Oro and colleagues found two sequences in the Gli1 protein � called Dn and Dc � that are recognized by the proteasome and facilitate Gli protein destruction. Mutations in these sequences (or "degrons" as they are called) prevent Gli1 degradation, causing, rather, the Gli1 protein to accumulate, and lead to accelerated tumorigenesis.

"Although we knew inducing hedgehog signaling in cells played an important role in human cancer induction and maintenance, we were puzzled by why it took so long in many cases. We were excited to find that normal cells have a way of protecting themselves from too much of the active Gli protein and surprised to discover that cancer cells appear to have disarmed that ability."

Dr. Oro and colleagues used transgenic mice expressing various forms of the Gli1 protein to demonstrate the link between Gli1 accumulation and tumor latency. Transgenic mice expressing wild-type Gli1 (in which the degrons are completely intact) develop basal cell carcinoma (BCC)-like tumor 6-8 weeks after birth. Mice expressing an altered form of either Dn or Dc (in which Gli1 is partially stabilized) develop BCC-like lesions at an earlier age. Remarkably, mice with mutated forms of both degrons (in which Gli1 is not degraded by the proteasome) die at birth, presenting severe ulcerating skin lesions similar to human BCCs.

This work convincingly shows that Gli protein accumulation contributes to the latency of Shh-dependent tumor formation, and that the modulation of Gli protein stability may thus represent a novel anticancer therapy. "We hope our studies will lead to ways to enhance the cell's ability to get rid of Gli and halt cancer development," adds Dr. Oro.

Genomics. 2006 Jan 21; [Epub ahead of print]

Overlapping and distinct transcriptional regulator properties of the GLI1 and GLI2 oncogenes.

Eichberger T, Sander V, Schnidar H, Regl G, Kasper M, Schmid C, Plamberger S, Kaser A, Aberger F, Frischauf AM.

Department of Molecular Biology, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria.

The GLI transcription factors mediate the hedgehog signal in development and carcinogenesis. Basal cell carcinoma can be caused by overexpression of either GLI1 or GLI2. Though GLI1 and GLI2 have identical or very similar DNA binding specificities, some of their activities are overlapping, some are clearly distinct. We analyzed target gene specificities of GLI1 and constitutively active GLI2 (GLI2DeltaN) by global expression profiling in an inducible, well-characterized HaCaT keratinocyte expression system. Four hundred fifty-six genes up- or downregulated at least twofold were identified. GLI target gene profiles correlated well with the biological activities of these transcription factors in hair follicles and basal cell carcinoma. Upregulation of largely overlapping sets of target genes was effected by both factors, repression occurred predominantly in response to GLI2. Also, significant quantitative differences in response to GLI1 and GLI2DeltaN were found for a small number of activated genes. Since we have not detected a putative processed GLI2 repressor, these results point to specific but indirect target gene repression by GLI2DeltaN via preferential activation of one or more negative regulators.

J Mol Diagn. 2006 Feb;8(1):76-83.

Multiple Gene Expression Analyses in Paraffin-Embedded Tissues by TaqMan Low-Density Array: Application to Hedgehog and Wnt Pathway Analysis in Ovarian Endometrioid Adenocarcinoma.

Steg A, Wang W, Blanquicett C, Grunda JM, Eltoum IA, Wang K, Buchsbaum DJ, Vickers SM, Russo S, Diasio RB, Frost AR, Lobuglio AF, Grizzle WE, Johnson MR.

Department of Clinical Pharmacology, 1824 6th Ave. South, Wallace Tumor Institute, Room 620, University of Alabama at Birmingham, Birmingham, AL 34294-3300. martin.johnson@ccc.uab.edu.

Recent studies have shown the hedgehog and Wnt families of signaling proteins to be associated with tumor initiation, growth, and survival. However, these pathways remain unexplored in ovarian endometrioid adenocarcinoma (OEA). Here, we describe a novel TaqMan low-density array to examine the expression of 26 and 20 genes in the hedgehog and Wnt pathways, respectively, in six matched snap-frozen and formalin-fixed, paraffin-embedded (FPE) OEA specimens. Expression values were normalized to uninvolved ovarian epithelium. Gene expression in matched frozen and FPE tissues demonstrated significant concordance (r = 0.92, P < 0.0001). However, comparison of amplified and unamplified RNA from frozen OEA tissues revealed an altered molecular profile in amplified RNA. Amplification of RNA from FPE tissues was not successful. The expression of Desert hedgehog (DHH), Indian hedgehog (IHH), Hedge-hog interacting protein (HHIP), Wnt10B, Wnt9B, and Wnt inhibitory factor (WIF1) were tumor-specific with no detectable expression in normal ovarian epithelium. In addition, several genes were significantly (P < 0.025) down-regulated in OEA, including cyclin E2, Porcupine, c-Myc, and Axin 2 (4.8-, 3.6-, 2.9-, and 1.9-fold, respectively). TaqMan low-density array provides an effective multivariate technique for examining gene expression in RNA isolated from either snap-frozen or archival FPE tissues and can identify tumor-specific genes, possibly leading to novel treatments.

Respir Res. 2006 Jan 26;7(1):15

Wnt signalling in lung development and diseases.

Pongracz JE, Stockley RA.

ABSTRACT: There are several signalling pathways involved in lung organogenesis including Notch, TGF-beta/BMP, Sonic hedgehog (Shh), FGF, EGF, and Wnt. Despite the widely acknowledged significance of Wnt signalling in embryonic lung development, the role of different Wnt pathways in lung pathologies has been slow to emerge. In this review, we will present a synopsis of current Wnt research with particular attention paid to the role of Wnt signals in lung development and in pulmonary diseases.

Am J Physiol Gastrointest Liver Physiol. 2006 Jan 26;

Increased Apoptosis and Accelerated Epithelial Migration Following Inhibition of Hedgehog Signaling in Adaptive Small Bowel Post-Resection.

Tang Y, Swietlicki EA, Jiang S, Buhman KK, Davidson NO, Burkly LC, Levin MS, Rubin DC.

Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO, USA.

The intestinal epithelium undergoes a marked adaptive response following loss of functional small bowel surface area, characterized by increased crypt cell proliferation and increased enterocyte migration from crypt to villus tip, resulting in villus hyperplasia and enhanced nutrient absorption. Hedgehog (Hh) signaling plays a critical role in regulating epithelial-mesenchymal interactions during morphogenesis of the embryonic intestine. Our previous studies showed that blocking Hh signaling in neonatal mice results in increased small intestinal epithelial crypt cell proliferation, and altered enterocyte fat absorption and morphology. Hh family members are also expressed in the adult intestine but their role in the mature small bowel is unclear. Using a model of intestinal adaptation following partial small bowel resection, the role of hedgehog signaling in adult gut was examined by determining the effects of blocking hedgehog signaling on the regenerative response following loss of functional surface area. Hh inactivating monoclonal antibodies or control antibodies were administered to mice that sustained a 50% intestinal resection. MRNA analyses of the preoperative ileum by quantitative real time PCR, revealed that Indian hedgehog was the most abundant Hh family member. The Hh receptor Patched was more abundant than Patched 2. Analyses of downstream targets of Hh signaling demonstrated that Gli3 was 2 fold more abundant than Gli1 and Gli2 and that BMP2 was most highly expressed compared with BMP1, 4 and 7. Following intestinal resection, the expression of Hh, Patched, Gli and most BMP genes was markedly downregulated in remnant ileum, and in anti Hh antibody treated mice, expression of Ptch 2 and Gli 1 were further suppressed. In Hh antibody treated mice following resection, enterocyte migration rate from crypt to villus tip was increased, and by two weeks postop, apoptosis was increased in the adaptive gut. However, crypt cell proliferation, villus height and crypt depth were not augmented. These data indicate that Hh signaling plays a role in adult gut epithelial homeostasis, by regulating epithelial cell migration from crypt to villus tip and by enhancing apoptosis.