Hedgehog signaling update

ATX expression and LPA signalling are vital for the development of the nervous system

Autotaxin (ATX) is a secreted glycoprotein widely present in biological fluids, originally isolated from the supernatant of melanoma cells as an autocrine motility stimulation factor. Its enzymatic product, lysophosphatidic acid (LPA), is a phospholipid mediator that evokes growth-factor-like responses in almost all cell types through G-protein coupled receptors. To assess the role of ATX and LPA signalling in pathophysiology, a conditional knockout mouse was created. Ubiquitous, obligatory deletion resulted to embryonic lethality most likely due to aberrant vascular branching morphogenesis and chorio-allantoic fusion. Moreover, the observed phenotype was shown to be entirely depended on embryonic, but not extraembryonic or maternal ATX expression. In addition, E9.5 ATX null mutants exhibited a failure of neural tube closure, most likely independent of the circulatory failure, which correlated with decreased cell proliferation and increased cell death. More importantly, neurite outgrowth in embryo explants was severely compromised in mutant embryos but could be rescued upon the addition of LPA, thus confirming a role for ATX and LPA signalling in the development of the nervous system. Finally, expression profiling of mutant embryos revealed attenuated embryonic expression of HIF-1a in the absence of ATX, suggesting a novel effector pathway of ATX/LPA.

RAB26 and RAB3D are direct transcriptional targets of MIST1 that regulate exocrine granule maturation

Little is known about how differentiating cells reorganize their cellular structure to perform specialized physiological functions. MIST1, an evolutionarily conserved transcription factor, is required for the formation of large, specialized secretory vesicles in gastric zymogenic (chief) cells (ZCs) as they differentiate from their mucous neck cell progenitors. Here, we show that MIST1 binds to highly conserved CATATG E-boxes to directly activate transcription of 6 genes, including those encoding the small GTPases RAB26 and RAB3D. We next show that RAB26 and RAB3D expression is significantly downregulated in Mist1(-)(/)(-) ZCs, suggesting that MIST1 establishes large secretory granules by inducing RAB transcription. To test this hypothesis, we transfected human gastric cancer cell lines stably expressing MIST1 with red fluorescent protein (RFP)-tagged pepsinogen C, a key secretory product of ZCs. Those cells upregulate expression of RAB26 and RAB3D to form large secretory granules, whereas control, non-MIST1-expressing cells do not. Moreover, granule formation in MIST1-expressing cells requires RAB activity because treatment with a RAB prenylation inhibitor and transfection of dominant negative RAB26 abrogate granule formation. Together, our data establish the molecular process by which a transcription factor can directly induce fundamental cellular architecture changes by increasing transcription of specific cellular effectors that act to organize a unique subcellular compartment.

Down-Regulation of SHH/BMP4 Signalling in Human Anorectal Malformations

The sonic hedgehog homologue (SHH)/bone morphogenetic protein 4 (BMP4) signalling pathway is involved in the morphogenesis of many organ systems. This study was designed to investigate the expression of SHH/BMP4 pathway components in human anorectal malformations (ARMs) and the relationship between expression of their genes and the occurrence of ARMs. Expression of SHH, GLI family zinc finger 2 (GLI2) and BMP4 mRNA in the posterior wall of the terminal rectum in 40 patients with ARMs (15 high-type and 25 low-type) and 10 normal controls was assessed by reverse transcription-polymerase chain reaction. Levels of SHH, GLI2 and BMP4 proteins were assessed by immunohistochemistry and Western blotting. The expressions of SHH, GLI2 and BMP4 were significantly lower in patients with high-type compared with those with low-type anomalies and controls. Patients with low-type ARMs differed from controls only in the expression of GLI2 mRNA. It is concluded that down-regulation of the SHH/BMP4 signalling pathway may be related to the occurrence of high-type ARMs, but the mechanism responsible for low-type ARMs remains unclear.

delta-EF1 is a negative regulator of Ihh in the developing growth plate

Indian hedgehog (Ihh) regulates proliferation and differentiation of chondrocytes in the growth plate. Although the biology of Ihh is currently well documented, its transcriptional regulation is poorly understood. delta-EF1 is a two-handed zinc finger/homeodomain transcriptional repressor. Targeted inactivation of mouse delta-EF1 leads to skeletal abnormalities including disorganized growth plates, shortening of long bones, and joint fusions, which are reminiscent of defects associated with deregulation of Ihh signaling. Here, we show that the absence of delta-EF1 results in delayed hypertrophic differentiation of chondrocytes and increased cell proliferation in the growth plate. Further, we demonstrate that delta-EF1 binds to the putative regulatory elements in intron 1 of Ihh in vitro and in vivo, resulting in down-regulation of Ihh expression. Finally, we show that delta-EF1 haploinsufficiency leads to a postnatal increase in trabecular bone mass associated with enhanced Ihh expression. In summary, we have identified delta-EF1 as an in vivo negative regulator of Ihh expression in the growth plate.

Microarray analysis of murine limb bud ectoderm and mesoderm after exposure to cadmium or acetazolamide

BACKGROUND

A variety of drugs, environmental chemicals, and physical agents induce a common limb malformation in the offspring of pregnant mice exposed on day 9 of gestation. This malformation, postaxial, right-sided forelimb ectrodactyly, is thought to arise via an alteration of hedgehog signaling.

METHODS

We have studied two of these teratogens, acetazolamide and cadmium, using the technique of microarray analysis of limb bud ectoderm and mesoderm to search for changes in gene expression that could indicate a common pathway to postaxial limb reduction.

RESULTS

Results indicated a generalized up-regulation of gene expression after exposure to acetazolamide but a generalized down-regulation due to cadmium exposure. An intriguing observation was a cadmium-induced reduction of Mt1 and Mt2 expression in the limb bud mesoderm indicating a lowering of embryonic zinc.

CONCLUSIONS

We propose that these two teratogens and others (valproic acid and ethanol) lower sonic hedgehog signaling by perturbation of zinc function in the sonic hedgehog protein.

The Hedgehog signalling pathway as a therapeutic target in early breast cancer development

The Hedgehog (Hh) signalling pathway is a highly conserved developmental pathway, which plays critical roles in patterning of the embryo through epithelial to mesenchymal signalling and the maintenance of stem cells in the adult organism. There is increasing evidence that this pathway is dysregulated in many malignancies, including breast cancer. While there has been a significant decrease in mortality from breast cancer, a number of treatment challenges remain, particularly in those tumours which develop resistance to endocrine-based therapy, or which lack expression of hormone or c-erbB2/HER2 receptors. Therapeutic manipulation of the Hh pathway as a potential cancer therapy is attracting great interest, with preclinical studies and clinical trials underway in a range of malignancies. This review highlights important recent developments that affect the potential of the Hh pathway as a novel therapeutic target in early breast cancer.

Sonic hedgehog is a potent chemoattractant for human monocytes: diabetes mellitus inhibits Sonic hedgehog-induced monocyte chemotaxis

The aim of the present study was to evaluate the expression of hedgehog (Hh) signaling molecules and the chemotactic activity of Sonic hedgehog (Shh) in monocytes from control (CTR) and diabetic patients with or without coronary artery disease (CAD). Previously several studies demonstrated that exogenous administration of Shh can induce angiogenesis and accelerate repair of ischemic myocardium and skeletal muscles. Blood samples were collected from (1) CTR (n = 25); (2) patients with stable CAD without diabetes mellitus (CAD−DM, n = 10); and (3) with stable CAD with DM (CAD+DM, n = 15). Monocytes were isolated by Percoll gradient and subjected to PCR and chemotaxis analysis. Hh signaling molecules were expressed in human monocytes, and Shh-induced monocyte chemotaxis. Shh-stimulated migration of monocytes from CTR measured 172.5 ± 90% and a maximal stimulation was observed at Shh concentration of 1 μg/ml. However, Shh failed to induce migration of monocytes from CAD+DM (94.3 ± 27%, P < 0.001 vs. CTR). The impaired response to Shh was associated with strong transcriptional upregulation of the receptor Ptc, while expression of downstream molecules was not altered. Moreover, Ptc is strongly expressed in macrophages of human aortic atherosclerotic plaque. Thus, Shh is a potent chemoattractant for monocytes and it activates classical signaling pathways related to migration. The Shh signaling was negatively affected by DM which might be involved in the pathogenesis of DM-related complications.

Pathogenesis of holoprosencephaly

Holoprosencephaly (HPE), the most common human forebrain malformation, occurs in 1 in 250 fetuses and 1 in 16,000 live births. HPE is etiologically heterogeneous, and its pathology is variable. Several mouse models of HPE have been generated, and some of the molecular causes of different forms of HPE and the mechanisms underlying its variable pathology have been revealed by these models. Herein, we summarize the current knowledge on the genetic alterations that cause HPE and discuss some important questions about this disease that remain to be answered.

Myogenesis and molecules - insights from zebrafish Danio rerio

Myogenesis is a fundamental process governing the formation of muscle in multicellular organisms. Recent studies in zebrafish Danio rerio have described the molecular events occurring during embryonic morphogenesis and have thus greatly clarified this process, helping to distinguish between the events that give rise to fast v. slow muscle. Coupled with the well-known Hedgehog signalling cascade and a wide variety of cellular processes during early development, the continual research on D. rerio slow muscle precursors has provided novel insights into their cellular behaviours in this organism. Similarly, analyses on fast muscle precursors have provided knowledge of the behaviour of a sub-set of epitheloid cells residing in the anterior domain of somites. Additionally, the findings by various groups on the roles of several molecules in somitic myogenesis have been clarified in the past year. In this study, the authors briefly review the current trends in the field of research of D. rerio trunk myogenesis.

Expression and regulation of hedgehog signaling pathway in pancreatic cancer

INTRODUCTION

Pancreatic cancer is an aggressive malignancy with a poor prognosis. The overall 5-year survival rate of pancreatic cancer is less than 5%, and has not improved significantly for years. Further understanding of the molecular carcinogenesis of pancreatic cancer is critical for designing effective ways to treat this type of malignancy.

METHODS

In this study, we examine expression of hedgehog signaling molecules in 54 surgically removed pancreatic cancer specimens as well as seven available pancreatic cancer cell lines.

RESULTS

We find that expression of Ptch is associated with tumor size, tumor differentiation, lymph node metastasis, and clinical stages, whereas expression of Smo is associated with tumor differentiation and lymph node metastasis. Our studies from pancreatic cancer cell lines indicate that targeted inhibition of hedgehog signaling by Smo signaling inhibitor KAAD-cyclopamine causes hedgehog target gene expression (Gli1) suppression, induces P21 expression and G1 cell population, and reduced expression of Cyclin D1 and IGF2.

CONCLUSIONS

These results indicate that hedgehog signaling activation is a very common event in pancreatic cancer and that targeted inhibition of hedgehog signaling may be effective in treatment of pancreatic cancer.

Complications of complexity: integrating environmental, genetic and hormonal control of insect diapause

Understanding gene interaction and pleiotropy are long-standing goals of developmental and evolutionary biology. We examine the genetic control of diapause in insects and show how the failure to recognize the difference between modular and gene pleiotropy has confounded our understanding of the genetic basis of this important phenotype. This has led to complications in understanding the role of the circadian clock in the control of diapause in Drosophila and other insects. We emphasize three successive modules - each containing functionally related genes - that lead to diapause: photoperiodism, hormonal events and diapause itself. Understanding the genetic basis for environmental control of diapause has wider implications for evolutionary response to rapid climate change and for the opportunity to observe evolutionary change in contemporary time.

Quantitative analysis of mRNA transcripts of Hox, SHH, PTCH, Wnt, and Fzd genes in canine hematopoietic progenitor cells and various in vitro colonies differentiated from the cells

Homeobox (Hox), Sonic hedgehog (SHH), and Wingless-type MMTV integration site family (Wnt) are known to modulate the self-renewal and expansion of hematopoietic progenitor/stem cells in humans and mice. Frizzled (Fzd) and Patched1 (PTCH1) represent the receptors of Wnt and SHH, respectively. In this study, the amounts of mRNA transcripts of the genes associated with the self-renewal of hematopoietic stem cells, HoxB3, HoxB4, HoxA10, Wnt5a, Wnt2b, Fzd1, Fzd6, SHH, and PTCH1, were measured in canine unfractionated bone marrow cells, CD34-enriched cells, and various colony-forming units in culture (CFU-C). Partial cDNA sequences of these 9 canine genes were determined in this study. Quantitative real-time polymerase chain reaction was employed to indicate their relative amounts of mRNA transcripts. Amounts of mRNA transcripts of HoxB3, HoxA10, PTCH1, and Wnt5a genes in canine CD34-enriched cell fraction were significantly larger than those in the CD34-depleted cell fraction. Amounts of mRNA transcripts of HoxB3, HoxA10, PTCH1, Wnt5a, and Wnt2b genes in various CFU-C cells were significantly smaller than those in the seeded CD34-enriched cell fraction. These results suggested important roles of the products of these genes in self-renewal, expansion, and survival of hematopoietic progenitor cells in dogs as shown in humans and rodents.

Ptch1 is required locally for mammary gland morphogenesis and systemically for ductal elongation

Systemic hormones and local growth factor-mediated tissue interactions are essential for mammary gland development. Using phenotypic and transplantation analyses of mice carrying the mesenchymal dysplasia (mes) allele of patched 1 (Ptch1(mes)), we found that Ptch1(mes) homozygosity led to either complete failure of gland development, failure of post-pubertal ductal elongation, or delayed growth with ductal dysplasia. All ductal phenotypes could be present in the same animal. Whole gland and epithelial fragment transplantation each yielded unique morphological defects indicating both epithelial and stromal functions for Ptch1. However, ductal elongation was rescued in all cases, suggesting an additional systemic function. Epithelial function was confirmed using a conditional null Ptch1 allele via MMTV-Cre-mediated disruption. In Ptch1(mes) homozygotes, failure of ductal elongation correlated with diminished estrogen and progesterone receptor expression, but could not be rescued by exogenous ovarian hormone treatment. By contrast, pituitary isografts were able to rescue the ductal elongation phenotype. Thus, Ptch1 functions in the mammary epithelium and stroma to regulate ductal morphogenesis, and in the pituitary to regulate ductal elongation and ovarian hormone responsiveness.

Hedgehog signaling is involved in differentiation of normal colonic tissue rather than in tumor proliferation

The Hedgehog (Hh) pathway is a main regulation cascade in embryonic differentiation. It is also present in adult tissues and unusual expression has been associated with formation of benign and malignant lesions. We examined the presence of the Hedgehog pathway in normal and pathological human colon tissue. Components investigated include Sonic (Shh), Indian (Ihh), and Desert Hedgehog (Dhh), Gli1, Gli2, Gli3, and Patched (Ptch). Pathological tissue samples comprised 23 benign and 20 malignant lesions of human colon. The influence of the Hedgehog pathway on differentiation and proliferation has been investigated by analyzing the effect of the pathway inhibitor Cyclopamine on human colon cancer cell lines HT29 and CaCo2. In normal colon, we detected expression of Shh and Dhh within the lining epithelium and Patched, Gli1, and Gli2 along the whole crypts. Within all benign lesions, positive staining of Shh, Dhh, Gli1, Gli2, and Ptch was detected. Expression of Shh and Dhh was restricted to single cell aggregates. Malignant lesions also displayed focal staining pattern for Shh and Dhh but to a much lesser extent. We conclude that Hedgehog signaling is involved rather in constant differentiation and renewing of the colonic lining epithelium than in cancer formation, growth, or proliferation.

Paracrine sonic hedgehog signalling by prostate cancer cells induces osteoblast differentiation

BACKGROUND

Sonic hedgehog (Shh) and components of its signalling pathway have been identified in human prostate carcinoma and increased levels of their expression appear to correlate with disease progression and metastasis. The mechanism through which Shh signalling could promote metastasis in bone, the most common site for prostate carcinoma metastasis, has not yet been investigated. The present study determined the effect of Shh signalling between prostate cancer cells and pre-osteoblasts on osteoblast differentiation, a requisite process for new bone formation that characterizes prostate carcinoma metastasis.

RESULTS

LNCaP human prostate cancer cells modified to overexpress Shh (designated LNShh cells) and MC3T3 mouse pre-osteoblasts were maintained as mixed populations within the same culture chamber. In this non-conventional mixed culture system, LNShh cells upregulated the expression of Shh target genes Gli1 and Patched 1 (Ptc1) in MC3T3 cells and this was inhibited by cyclopamine, a specific chemical inhibitor of hedgehog signalling. Concomitantly, MC3T3 cells exhibited time-dependent decreased cell proliferation, upregulated alkaline phosphatase Akp2 gene expression, and increased alkaline phosphatase activity indicative of early phase osteoblast differentiation. LNShh cell-induced differentiation was inhibited in MC3T3 cells stably transfected with a dominant negative form of Gli1, a transcription factor that mediates Shh signalling. Interestingly, LNShh cells did not significantly increase the endogenous expression of the osteoblast differentiation transcription factor Runx2 and its target genes osteocalcin and osteopontin. Consistent with these results, exogenous Shh peptide did not upregulate Runx2 expression in MC3T3 cells. However, Runx2 levels were increased in MC3T3 cells by ascorbic acid, a known stimulator of osteoblast differentiation.

CONCLUSION

Altogether, these data demonstrate that Shh-expressing prostate cancer cells can directly and specifically induce differentiation in pre-osteoblasts via a Gli1-dependent mechanism that does not require transcriptional upregulation of Runx2. Paracrine activation of the Shh pathway in osteoblast progenitors and subsequent induction of osteoblast differentiation could be a mechanism through which high levels of Shh expression in prostate carcinoma contribute to bone metastasis. Targeting of paracrine Shh signalling may provide an effective therapeutic strategy against prostate carcinoma metastasis in bone.

A SHH-independent regulation of Gli3 is a significant determinant of anteroposterior patterning of the limb bud

The family of GLI proteins (GLI1-3) comprises the intracellular mediators of the hedgehog pathway, which regulates a myriad of developmental processes, one of which is limb development. Whereas GLI1 and GLI2 seem to be dispensable during limb development, GLI3 is especially crucial since all GLI3-associated human congenital diseases comprise limb malformations. Furthermore, Gli3(-/-) mouse embryos exhibit pronounced polydactyly in conjunction with a loss of digit identities. Here we examined how the quantity of GLI3 contributes to its function by using different Gli3 mutants in order to vary overall GLI3 levels. In addition, we made use of the Gli3(Delta699) allele, which encodes a C-terminally truncated version of GLI3, thus mimicking the processed GLI3 isoform (GLI3R). The Gli3(Delta699) mutant made it feasible to analyze isoform-specific contributions of GLI3 within the context of anteroposterior patterning of the limb bud. We revealed a so far unappreciated variation in the quantitative demand for GLI3 within different phases and aspects of distal limb formation. In addition, our analyses provide evidence that unprocessed full-length GLI3 is dispensable for anteroposterior patterning of the limb bud. Instead, digit identities are most likely defined by GLI3 repressor activity alone. Furthermore, we present evidence that the anteroposterior grading of GLI3 activity by the action of SHH is supported by a prototype patterning, which regulates Gli3 independently from SHH.

Molecular targeting therapy for pancreatic cancer: current knowledge and perspectives from bench to bedside

Current medical interventions for pancreatic cancer are insufficient. Recent molecular investigations have elucidated complex genetic mechanisms of cancer that especially involve multiple signal transduction pathways; this enables us to develop molecular medicines targeting specific genetic molecules in the pathways. These molecular medicines seem to promise clues for curing cancers, including pancreatic cancer. This review describes current knowledge and perspectives regarding the development of molecular medicines for pancreatic cancer by focusing on growth factor receptor systems and three major signal transduction pathways: the RAS-MAPK, PI3K-AKT-mTOR, and hedgehog pathways.

Assessing the molecular genetics of the development of executive attention in children: focus on genetic pathways related to the anterior cingulate cortex and dopamine

It is well known that children show gradual and protracted improvement in an array of behaviors involved in the conscious control of thought and emotion. Non-invasive neuroimaging in developing populations has revealed many neural correlates of behavior, particularly in the developing cingulate cortex and frontostriatal circuits. These brain regions, themselves, undergo protracted molecular and cellular change in the first two decades of human development and, as such, are ideal regions of interest for cognitive- and imaging-genetic studies that seek to link processes at the biochemical and synaptic levels to brain activity and behavior. We review our research to date that employs both adult and child-friendly versions of the attention network task (ANT) in an effort to begin to describe the role of specific genes in the assembly of a functional attention system. Presently, we constrain our predictions for genetic association studies by focusing on the role of the anterior cingulate cortex (ACC) and of dopamine in the development of executive attention.

Circulatory lipid transport: lipoprotein assembly and function from an evolutionary perspective

Circulatory transport of neutral lipids (fat) in animals relies on members of the large lipid transfer protein (LLTP) superfamily, including mammalian apolipoprotein B (apoB) and insect apolipophorin II/I (apoLp-II/I). Latter proteins, which constitute the structural basis for the assembly of various lipoproteins, acquire lipids through microsomal triglyceride transfer protein (MTP)--another LLTP family member--and bind them by means of amphipathic structures. Comparative research reveals that LLTPs have evolved from the earliest animals and additionally highlights the structural and functional adaptations in these lipid carriers. For instance, in contrast to mammalian apoB, the insect apoB homologue, apoLp-II/I, is post-translationally cleaved by a furin, resulting in their appearance of two non-exchangeable apolipoproteins in the insect low-density lipoprotein (LDL) homologue, high-density lipophorin (HDLp). An important difference between mammalian and insect lipoproteins relates to the mechanism of lipid delivery. Whereas in mammals, endocytic uptake of lipoprotein particles, mediated via members of the LDL receptor (LDLR) family, results in their degradation in lysosomes, the insect HDLp was shown to act as a reusable lipid shuttle which is capable of reloading lipid. Although the recent identification of a lipophorin receptor (LpR), a homologue of LDLR, reveals that endocytic uptake of HDLp may constitute an additional mechanism of lipid delivery, the endocytosed lipoprotein appears to be recycled in a transferrin-like manner. Binding studies indicate that the HDLp-LpR complex, in contrast to the LDL-LDLR complex, is resistant to dissociation at endosomal pH as well as by treatment with EDTA mimicking the drop in Ca(2+) concentration in the endosome. This remarkable stability of the ligand-receptor complex may provide a crucial key to the recycling mechanism. Based on the binding and dissociation capacities of mutant and hybrid receptors, the specific binding interaction of the ligand-binding domain of the receptor with HDLp was characterized. These structural similarities and functional adaptations of the lipid transport systems operative in mammals and insects are discussed from an evolutionary perspective.

Comparative expression of Hedgehog ligands at different stages of prostate carcinoma progression

Recent studies have revealed the potential involvement of Hedgehog (Hh) signalling in proliferation and invasive behaviour of prostate carcinoma (PCa). The aim of this study was to specify the role of Sonic Hh (Shh), Desert Hh (Dhh) and Indian Hh (Ihh) in the natural history of PCa. Hh ligands expression was compared in primary hormone-naive PCa (HNPC), hormone-treated PCa (HTPC) and hormone-refractory PCa (HRPC), using immunohistochemistry. Shh and Dhh were expressed by both epithelial and stromal cells of prostate tissues. Ihh was only expressed by stromal cells. For the three ligands, mRNA and immunostaining were not correlated. In HNPC, Shh epithelial expression was significantly associated with high Gleason scores (p = 0.03), metastatic lymph nodes (p = 0.004) and Dhh epithelial staining was associated with high pT stages (p = 0.003), seminal vesicle invasion (p = 0.03) and bladder neck invasion (p = 0.0008). Negative Shh staining in stromal cells was associated with high Gleason scores (p = 0.015), high pT stages (p = 0.01) and bladder neck invasion (p = 0.04). Concomitant absence of Shh and Dhh expression in stromal cells was an independent prognostic parameter for biological recurrence on multivariate analysis (p = 0.01). Epithelial expression of Shh and Dhh was increased in HTPC compared to HNPC (p = 0.02 and p = 0.04). Interestingly, in vitro, transcript analysis also showed increased expression of these 2 Hh ligands when androgen-sensitive LNCaP cells were maintained in androgen-free medium mimicking hormonal therapy. Epithelial expression of Dhh was increased (p < 0.0001) in HRPC compared to HNPC, while stromal expression of Shh and Dhh was decreased (p < 0.0001). In conclusion, the Hh signalling pathway is associated with pejorative pathological parameters in HNPC and is up-regulated in epithelial cells of HTPC and HRPC. Moreover, the lack of Hh molecules in stromal cells seems to be associated with invasive and hormone-refractory behaviours and suggests specific changes in stromal-epithelial crosstalks during PCa progression.

Inhibition of microtubule assembly in osteoblasts stimulates bone morphogenetic protein 2 expression and bone formation through transcription factor Gli2

Bone morphogenetic protein 2 (BMP-2) is essential for postnatal bone formation and fracture repair. By screening chemical libraries for BMP-2 mimics using a cell-based assay, we identified inhibitors of microtubule assembly as stimulators of BMP-2 transcription. These microtubule inhibitors increased osteoblast differentiation in vitro, stimulated periosteal bone formation when injected locally over murine calvaria, and enhanced trabecular bone formation when administered systemically in vivo. To explore molecular mechanisms mediating these responses, we examined effects of microtubule inhibitors on the hedgehog (Hh) pathway, since this pathway is known to regulate BMP-2 transcription in osteoblasts and microtubules have been shown to be involved in Hh signaling in Drosophila. Here we show that in osteoblasts, inhibition of microtubule assembly increased cytoplasmic levels and transcriptional activity of Gli2, a transcriptional mediator of Hh signaling that we have previously shown to enhance BMP-2 expression in osteoblasts (M. Zhao et al., Mol. Cell. Biol. 26:6197-6208, 2006). Microtubule inhibition blocked beta-TrCP-mediated proteasomal processing of Gli2 in osteoblasts. In summary, inhibition of microtubule assembly enhances BMP-2 gene transcription and subsequent bone formation, in part, through inhibiting proteasomal processing of Gli2 and increasing intracellular Gli2 concentrations.

The Hedgehog protein family

The Hedgehog (Hh) pathway is one of the fundamental signal transduction pathways in animal development and is also involved in stem-cell maintenance and carcinogenesis. The hedgehog (hh) gene was first discovered in Drosophila, and members of the family have since been found in most metazoa. Hh proteins are composed of two domains, an amino-terminal domain HhN, which has the biological signal activity, and a carboxy-terminal autocatalytic domain HhC, which cleaves Hh into two parts in an intramolecular reaction and adds a cholesterol moiety to HhN. HhC has sequence similarity to the self-splicing inteins, and the shared region is termed Hint. New classes of proteins containing the Hint domain have been discovered recently in bacteria and eukaryotes, and the Hog class, of which Hh proteins comprise one family, is widespread throughout eukaryotes. The non-Hh Hog proteins have carboxy-terminal domains (the Hog domain) highly similar to HhC, although they lack the HhN domain, and instead have other amino-terminal domains. Hog proteins are found in many protists, but the Hh family emerged only in early metazoan evolution. HhN is modified by cholesterol at its carboxyl terminus and by palmitate at its amino terminus in both flies and mammals. The modified HhN is released from the cell and travels through the extracellular space. On binding its receptor Patched, it relieves the inhibition that Patched exerts on Smoothened, a G-protein-coupled receptor. The resulting signaling cascade converges on the transcription factor Cubitus interruptus (Ci), or its mammalian counterparts, the Gli proteins, which activate or repress target genes.

Two new patients with Curry-Jones syndrome with trichoblastoma and medulloblastoma suggest an etiologic role of the sonic hedgehog-patched-GLI pathway

Curry-Jones syndrome (OMIM #601707) is a rare multiple malformation disorder of unknown etiology, associated with brain and skull abnormalities, polysyndactyly, and defects of the eyes, skin and gastrointestinal tract. We report on two new cases of Curry-Jones syndrome with previously unreported features, including benign and malignant neoplasms. The first patient had typical features of Curry-Jones syndrome as well as multiple intra-abdominal smooth muscle hamartomas and trichoblastoma of the skin. The second patient was born with occipital meningoceles and developed a desmoplastic medulloblastoma. Routine lymphocyte karyotype, GLI3 gene analysis and Patched (PTCH) gene analysis on both patients and chromosome microarray analysis on the first patient were normal. We review the previously reported cases of Curry-Jones syndrome and compare our patients' findings. In view of the association of trichoblastoma with basal cell carcinoma and desmoplastic medulloblastoma with nevoid basal cell carcinoma syndrome (NBCCS) and PTCH mutations, we hypothesize that Curry-Jones syndrome is caused by malfunction of an element in the sonic hedgehog pathway.

Maintenance of the BMP4-dependent stress erythropoiesis pathway in the murine spleen requires hedgehog signaling

The production of mature cells necessitates that lineage-committed progenitor cells be constantly generated from multipotential progenitors. In addition, the ability to respond rapidly to physiologic stresses requires that the signals that regulate the maintenance of progenitor populations be coordinated with the signals that promote differentiation of progenitors. Here we examine the signals that are necessary for the maintenance of the BMP4-dependent stress erythropoiesis pathway. Our previous work demonstrated that BMP4, stem cell factor, and hypoxia act in concert to promote the expansion of a specialized population of stress erythroid progenitors in the spleen during the recovery from acute anemia. Our analysis shows that acute anemia leads to an almost complete mobilization of BMP4-responsive stress erythroid burst-forming units; therefore, new stress progenitors must be recruited to the spleen to replenish this system. We show that bone marrow cells can home to the spleen and, in response to a signal in the spleen microenvironment, Hedgehog, they develop into BMP4-responsive stress progenitors. Hedgehog induces the expression of BMP4, and together these 2 signals are required for the development of BMP4-responsive stress progenitors. These data demonstrate that the interplay between these 2 signals is crucial for maintenance of this stress response pathway.

Frequency of holoprosencephaly in the International Clearinghouse Birth Defects Surveillance Systems: searching for population variations

BACKGROUND

Holoprosencephaly (HPE) is a developmental field defect of the brain that results in incomplete separation of the cerebral hemispheres that includes less severe phenotypes, such as arhinencephaly and single median maxillary central incisor. Information on the epidemiology of HPE is limited, both because few population-based studies have been reported, and because small studies must observe a greater number of years in order to accumulate sufficient numbers of births for a reliable estimate.

METHODS

We collected data from 2000 through 2004 from 24 of the 46 Birth Defects Registry Members of the International Clearinghouse for Birth Defects Surveillance and Research. This study is based on more than 7 million births in various areas from North and South America, Europe, and Australia.

RESULTS

A total of 963 HPE cases were registered, yielding an overall prevalence of 1.31 per 10,000 births. Because the estimate was heterogeneous, possible causes of variations among populations were analyzed: random variation, under-reporting and over-reporting bias, variation in proportion of termination of pregnancies among all registered cases and real differences among populations.

CONCLUSIONS

The data do not suggest large differences in total prevalence of HPE among the studied populations that would be useful to generate etiological hypotheses.

Zic2-associated holoprosencephaly is caused by a transient defect in the organizer region during gastrulation

The putative transcription factor ZIC2 is associated with a defect of forebrain development, known as Holoprosencephaly (HPE), in humans and mouse, yet the mechanism by which aberrant ZIC2 function causes classical HPE is unexplained. The zinc finger domain of all mammalian Zic genes is highly homologous with that of the Gli genes, which are transcriptional mediators of Shh signalling. Mutations in Shh and many other Hh pathway members cause HPE and it has been proposed that Zic2 acts within the Shh pathway to cause HPE. We have investigated the embryological cause of Zic2-associated HPE and the relationship between Zic2 and the Shh pathway using mouse genetics. We show that Zic2 does not interact with Shh to produce HPE. Moreover, molecular defects that are able to account for the HPE phenotype are present in Zic2 mutants before the onset of Shh signalling. Mutation of Zic2 causes HPE via a transient defect in the function of the organizer region at mid-gastrulation which causes an arrest in the development of the prechordal plate (PCP), a structure required for forebrain midline morphogenesis. The analysis provides genetic evidence that Zic2 functions during organizer formation and that the PCP develops via a multi-step process.

Gli1 contributes to the invasiveness of pancreatic cancer through matrix metalloproteinase-9 activation

The hedgehog (Hh) signaling pathway has been reported to be associated with the growth of pancreatic cancer, but its role in the invasive phenotype is poorly understood. Therefore, we investigated the role of the Hh pathway in pancreatic cancer cell invasiveness using a Matrigel invasion assay. Blockade of the Hh pathway by cyclopamine inhibited pancreatic cancer cell invasion in association with a decreased expression of matrix metalloproteinase (MMP)-9. By contrast, activation of the Hh pathway by the addition of exogenous Sonic hedgehog increased cell invasion and MMP-9 expression. Stable transfection of pancreatic cancer cells with Gli1 increased their invasiveness, which was associated with activation of MMP-9. We also showed that inhibition of MMP-9 by small interfering RNA blocked the increased invasiveness of Gli1-transfected cells. Furthermore, inhibition of Gli1 by small interfering RNA suppressed the invasiveness and MMP-9 expression of pancreatic cancer cells. Taken together, these findings suggest that members of the Hh pathway, especially Gli1, play an important role in the invasiveness of pancreatic cancer cells through the regulation of MMP-9 expression.

Cyclopamine inhibition of human breast cancer cell growth independent of Smoothened (Smo)

Altered hedgehog signaling is implicated in the development of approximately 20-25% of all cancers, especially those of soft tissues. Genetic evidence in mice as well as immunolocalization studies in human breast cancer specimens suggest that deregulated hedgehog signaling may contribute to breast cancer development. Indeed, two recent studies demonstrated that anchorage-dependent growth of some human breast cancer cell lines is impaired by cyclopamine, a potent hedgehog signaling antagonist targeting the Smoothened (SMO) protein. However, specificity of cyclopamine at the dosage required for growth inhibition (> or =10 microM) remained an open question. In this paper we demonstrate that hedgehog signaling antagonists, including cyclopamine, and a second compound, CUR0199691, can inhibit growth of estrogen receptor (ER)-positive and ER-negative tumorigenic breast cancer cells at elevated doses. However, our results indicate that, for most breast cancer cell lines, growth inhibition by these compounds can be independent of detectable Smo gene expression. Rather, our results suggest that cyclopamine and CUR0199691 have unique secondary molecular targets at the dosages required for growth inhibition that are unrelated to hedgehog signaling.

Age-related cone abnormalities in zebrafish with genetic lesions in sonic hedgehog

PURPOSE

Sonic hedgehog (Shh) signaling is essential for photoreceptor differentiation and retinal cell survival in embryonic zebrafish. The study was conducted to determine whether adult heterozygous carriers of mutant alleles for the shh gene display retinal abnormalities.

METHODS

Retinal cryosections from young, middle-aged, and senescent wild-type and sonic-you(+/-) (syu(+/-)) zebrafish were probed with retinal cell type-specific markers. Contralateral retinal flatmounts from these fish, and from adult albino zebrafish subjected to light-induced photoreceptor damage followed by regeneration, were hybridized with blue cone opsin cRNA for quantitative analysis of the blue cone pattern. Retinal expression of shh mRNA was measured by quantitative RT-PCR.

RESULTS

Regions of cone loss and abnormal cone morphology were observed in the oldest syu(+/-) zebrafish, although no other retinal cell type was affected. This phenotype was age-related and genotype-specific. Cone distribution in the oldest syu(+/-) zebrafish was predominantly random, as assessed by measuring the short-range pattern, whereas that of wild-type fish and the younger syu(+/-) zebrafish was statistically regular. A measure of long-range pattern revealed atypical cone aggregation in the oldest syu(+/-) zebrafish. The light-treated albino zebrafish displayed random cone patterns immediately after light toxicity, but showed cone aggregation on regeneration. Retinas from the syu(+/-) fish showed reduced expression of shh mRNA compared with those of wild-type siblings.

CONCLUSIONS

The syu(+/-) zebrafish presents a model for the study of hereditary age-related cone abnormalities. The syu(+/-) retinas most likely experience progressive cone photoreceptor loss, accompanied by cone regeneration. Shh signaling may be required to maintain cone viability throughout life.

Expression patterns and polymorphisms of PTCH in Chinese hepatocellular carcinoma patients

Aberrant activation of Hedgehog signaling pathway leads to pathological consequences in a variety of human tumors. PTCH (PTCH1), the receptor of Hedgehog pathway, is reported to function as a gatekeeper in tumor formation. Here we report, by semi-quantitative RT-PCR, PTCH expression was found in 38 hepatocellular carcinoma (HCC) patients (66%). Evidences from real time quantitative RT-PCR further indicate that compared to their matched nontumorous liver tissue, PTCH exhibit a higher expression in well and moderate differentiated tumor, but a lower expression in poorly differentiated tumor. Immunohistochemical staining showed PTCH protein was detected in the cytoplasm of 56.3% HCC samples (9/16). For the first time, we investigate the polymorphisms of PTCH in HCC. First we sequenced the recognized mutation hot spots regions of PTCH of 38 HCC samples. Two previously reported single nucleotide polymorphisms (SNPs) and a novel SNP A1056G were identified. Then we examined these three SNPs in 171 HCC samples and 162 normal liver samples. However, statistic analysis showed none of these SNPs was statistically significant for association with HCC. In conclusion, our data suggest that PTCH is involved in early stage tumor development and the Hh pathway in Chinese HCC is activated by ligand expression but not by mutation.

Apoptosis and pathogenesis of melanoma and nonmelanoma skin cancer

Skin cancers, i.e., basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and melanoma, belong to the most frequent tumors. Their formation is based on constitutional and/or inherited factors usually combined with environmental factors, mainly UV-irradiation through long term sun exposure. UV-light can randomly induce DNA damage in keratinocytes, but it can also mutate genes essential for control and surveillance in the skin epidermis. Various repair and safety mechanisms exist to maintain the integrity of the skin epidermis. For example, UV-light damaged DNA is repaired and if this is not possible, the DNA damaged cells are eliminated by apoptosis (sunburn cells). This occurs under the control of the p53 suppressor gene. Fas-ligand (FasL), a member of the tumor necrosis superfamily, which is preferentially expressed in the basal layer of the skin epidermis, is a key surveillance molecule involved in the elimination of sunburn cells, but also in the prevention of cell transformation. However, UV light exposure downregulates FasL expression in keratinocytes and melanocytes leading to the loss of its sensor function. This increases the risk that transformed cells are not eliminated anymore. Moreover, important control and surveillance genes can also be directly affected by UV-light. Mutation in the p53 gene is the starting point for the formation of SCC and some forms of BCC. Other BCCs originate through UV light mediated mutations of genes of the hedgehog signaling pathway which are essential for the maintainance of cell growth and differentiation. The transcription factor Gli2 plays a key role within this pathway, indeed, Gli2 is responsible for the marked apoptosis resistance of the BCCs. The formation of malignant melanoma is very complex. Melanocytes form nevi and from the nevi melanoma can develop through mutations in various genes. Once the keratinocytes or melanocytes have been transformed they re-express FasL which may allow the expanding tumor to evade the attack of immune effector cells. FasL which is involved in immune evasion or genes which govern the apoptosis resistance, e.g., Gli2 could therefore be prime targets to prevent tumor formation and growth. Attempts to silence these genes by RNA interference using gene specific short interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs) have been functionally successful not only in tissue cultures and tumor tissues, but also in a mouse model. Thus, siRNAs and/or shRNAs may become a novel and promising approach to treat skin cancers at an early stage.

Vsx2/Chx10 ensures the correct timing and magnitude of Hedgehog signaling in the mouse retina

Vertebrate retinal progenitor cells (RPCs) undergo a robust proliferative expansion to produce enough cells for the retina to form appropriately. Vsx2 (formerly Chx10), a homeodomain protein expressed in RPCs, is required for sufficient proliferation to occur. Sonic Hedgehog protein (SHH), secreted by retinal ganglion cells (RGCs), activates Hedgehog (Hh) signaling in RPCs and is also required for sufficient proliferation to occur. Therefore, we sought to determine if reduced Hh signaling is a contributing factor to the proliferation changes that occur in the absence of Vsx2. To do this, we examined Shh expression and Hh signaling activity in the homozygous ocular retardation J (orJ) mouse, which harbors a recessive null allele in the Vsx2 gene. We found that Shh expression and Hh signaling activity are delayed during early retinal development in orJ mice and this correlates with a delay in the onset of RGC differentiation. At birth, reduced expression of genes regulated by Hh signaling was observed despite the production of SHH ligand. orJ RPCs respond to pre-processed recombinant SHH ligand (SHH-N) in explant culture as evidenced by increased proliferation and expression of Hh target genes. Interestingly, proliferation in the orJ retina is further inhibited by cyclopamine, an antagonist of Hh signaling. Our results suggest that reduced Hh signaling contributes to the reduced level of RPC proliferation in the orJ retina, thereby revealing a role for Vsx2 in mediating mitogen signaling.

Evolution of hedgehog and hedgehog-related genes, their origin from Hog proteins in ancestral eukaryotes and discovery of a novel Hint motif

Background

The Hedgehog (Hh) signaling pathway plays important roles in human and animal development as well as in carcinogenesis. Hh molecules have been found in both protostomes and deuterostomes, but curiously the nematode Caenorhabditis elegans lacks a bona-fide Hh. Instead a series of Hh-related proteins are found, which share the Hint/Hog domain with Hh, but have distinct N-termini.

Results

We performed extensive genome searches such as the cnidarian Nematostella vectensis and several nematodes to gain further insights into Hh evolution. We found six genes in N. vectensis with a relationship to Hh: two Hh genes, one gene with a Hh N-terminal domain fused to a Willebrand factor type A domain (VWA), and three genes containing Hint/Hog domains with distinct novel N-termini. In the nematode Brugia malayi we find the same types of hh-related genes as in C. elegans. In the more distantly related Enoplea nematodes Xiphinema and Trichinella spiralis we find a bona-fide Hh. In addition, T. spiralis also has a quahog gene like C. elegans, and there are several additional hh-related genes, some of which have secreted N-terminal domains of only 15 to 25 residues. Examination of other Hh pathway components revealed that T. spiralis - like C. elegans - lacks some of these components. Extending our search to all eukaryotes, we recovered genes containing a Hog domain similar to Hh from many different groups of protists. In addition, we identified a novel Hint gene family present in many eukaryote groups that encodes a VWA domain fused to a distinct Hint domain we call Vint. Further members of a poorly characterized Hint family were also retrieved from bacteria.

Conclusion

In Cnidaria and nematodes the evolution of hh genes occurred in parallel to the evolution of other genes that contain a Hog domain but have different N-termini. The fact that Hog genes comprising a secreted N-terminus and a Hog domain are found in many protists indicates that this gene family must have arisen in very early eukaryotic evolution, and gave rise eventually to hh and hh-related genes in animals. The results indicate a hitherto unsuspected ability of Hog domain encoding genes to evolve new N-termini. In one instance in Cnidaria, the Hh N-terminal signaling domain is associated with a VWA domain and lacks a Hog domain, suggesting a modular mode of evolution also for the N-terminal domain. The Hog domain proteins, the inteins and VWA-Vint proteins are three families of Hint domain proteins that evolved in parallel in eukaryotes.

A novel role for zebrafish zic2a during forebrain development

Patterns of transcription factor expression establish a blueprint for the vertebrate forebrain early in embryogenesis. In the future diencephalon, several genes with patterned expression have been identified, yet their specific functions and interactions between them are not well understood. We have uncovered a crucial role for one such gene, zic2a, during formation of the anterior diencephalon in zebrafish. We show that zic2a is required for transcription of the prethalamic markers arx and dlx2a. This function is required during early steps of prethalamic development, soon after its specification. zic genes are evolutionarily related to glis, transcription factors that mediate hedgehog signaling. Intriguingly, the hedgehog signaling pathway also acts to promote development of the prethalamus. We asked if zic2a interacts with hedgehog signaling in the context of forebrain development in zebrafish. Our data show that hedgehog signaling and zic2a function at different times, and therefore act in parallel pathways during forebrain development. Taken together, our results identify Zic2a as a novel regulator of prethalamic development, and show that it functions independently of hedgehog signaling.

Expression of Fgf15 is regulated by both activator and repressor forms of Gli2 in vitro

Fibroblast growth factor 15 (Fgf15) is expressed in the medial region of diencephalon and midbrain by the seven-somite stage. In the previous studies, we showed that Sonic hedgehog signaling through Gli protein is required for Fgf15 expression in this region. The Fgf15 expression domain overlapped with that of Gli2 and the Gli-binding site (GliBs) is located in the 3.6-kb 5'-flanking enhancer/promoter region of the Fgf15 gene. In this study, we identified the two additional Gli-binding sites in row, called Gli-responsive elements (GliREs). Chromatin immunoprecipitation assay indicated that Gli2 directly binds to GliREs. The results from luciferase assays indicated that the Gli2 activator form binds to the GliBS and that the Gli2 repressor form binds to the GliREs. These findings suggest that the repressor form of Gli2 preferentially binds to the GliREs to control Fgf15 expression.

Lrp6 is required for convergent extension during Xenopus gastrulation

Wnt signaling regulates beta-catenin-mediated gene transcription and planar cell polarity (PCP). The Wnt co-receptor, Lrp6, is required for signaling along the beta-catenin arm. We show that Lrp6 downregulation (by morpholino injection) or overexpression in Xenopus embryos disrupts convergent extension, a hallmark feature of Wnt/PCP components. In embryos with decreased Lrp6 levels, cells of the dorsal marginal zone (DMZ), which undergoes extensive cellular rearrangements during gastrulation, exhibit decreased length:width ratios, decreased migration, and increased numbers of transient cytoplasmic protrusions. We show that Lrp6 opposes Wnt11 activity and localizes to the posterior edge of migrating DMZ cells and that Lrp6 downregulation enhances cortical and nuclear localization of Dsh and phospho-JNK, respectively. Taken together, these data suggest that Lrp6 inhibits Wnt/PCP signaling. Finally, we identify the region of the Lrp6 protein with Wnt/PCP activity to a stretch of 36 amino acids, distinct from regions required for Wnt/beta-catenin signaling. We propose a model in which Lrp6 plays a critical role in the switch from Wnt/PCP to Wnt/beta-catenin signaling.

Gli2 upregulates cFlip and renders basal cell carcinoma cells resistant to death ligand-mediated apoptosis

Mutations in the Hedgehog signaling pathway is responsible for the formation of various cancers, including some forms of basal cell carcinoma (BCC). Uncontrolled Hedgehog signaling leads to overexpression of the zinc-finger Gli transcription factors, among which Gli2 plays a central role. We found that high Gli2 expression induced the concomitant high expression of the caspase 8 inhibitor, cFlip, and thereby counteracts death-ligand-mediated apoptosis. By investigating the cFlip promoter, Gli2 binding sites were identified and confirmed. Gli2 gene silencing by RNA interference broke the apoptosis resistance via cFlip downregulation. The direct functional connection between Gli2 and cFlip was not only demonstrated in a keratinocytic cell line but also in BCC tissue. As cFlip and Bcl-2 are highly expressed in BCCs, as a consequence of high Gli2 expression, this may explain the marked resistance of the tumor to the extrinsic and intrinsic apoptotic pathway. We could now demonstrate that Gli2 gene silencing in BCC tissues made the tumor sensitive to TRAIL (tumor necrosis factor-related apoptosis-inducing ligand)-mediated cell death by downregulating cFlip. As Gli2 silencing does not only downregulate cFlip, but also Bcl-2, Gli2 could be a key target for a novel therapeutic approach in tumors with dysregulated Hedgehog signaling.

Mutations in BMP4 cause eye, brain, and digit developmental anomalies: overlap between the BMP4 and hedgehog signaling pathways

Developmental ocular malformations, including anophthalmia-microphthalmia (AM), are heterogeneous disorders with frequent sporadic or non-Mendelian inheritance. Recurrent interstitial deletions of 14q22-q23 have been associated with AM, sometimes with poly/syndactyly and hypopituitarism. We identify two further cases of AM (one with associated pituitary anomalies) with a 14q22-q23 deletion. Using a positional candidate gene approach, we analyzed the BMP4 (Bone Morphogenetic Protein-4) gene and identified a frameshift mutation (c.226del2, p.S76fs104X) that segregated with AM, retinal dystrophy, myopia, brain anomalies, and polydactyly in a family and a nonconservative missense mutation (c.278A-->G, p.E93G) in a highly conserved base in another family. MR imaging and tractography in the c.226del2 proband revealed a primary brain developmental disorder affecting thalamostriatal and callosal pathways, also present in the affected grandmother. Using in situ hybridization in human embryos, we demonstrate expression of BMP4 in optic vesicle, developing retina and lens, pituitary region, and digits strongly supporting BMP4 as a causative gene for AM, pituitary, and poly/syndactyly. Because BMP4 interacts with HH signaling genes in animals, we evaluated gene expression in human embryos and demonstrate cotemporal and cospatial expression of BMP4 and HH signaling genes. We also identified four cases, some of whom had retinal dystrophy, with "low-penetrant" mutations in both BMP4 and HH signaling genes: SHH (Sonic Hedgehog) or PTCH1 (Patched). We propose that BMP4 is a major gene for AM and/or retinal dystrophy and brain anomalies and may be a candidate gene for myopia and poly/syndactyly. Our finding of low-penetrant variants in BMP4 and HH signaling partners is suggestive of an interaction between the two pathways in humans.

Gli-1 siRNA induced apoptosis in Huh7 cells

AIM: To investigate the effects of Gli-1 small interference RNA (siRNA) on Huh7 cells, and the change of Bcl-2 expression in Huh7 cells.

METHODS: Human hepatocellular carcinoma cells Huh7 were used. Cell viability was analyzed by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. The expressions of Gli-1 and Bcl-2 family members were detected by RT-PCR and Western blot. Apoptosis was detected by Flow cytometry using propidium iodide, measured by Hoechst 33258 staining using Advanced Fluorescence Microscopy and caspase-3 enzymatic assay. Cell growth was analyzed after treatment with Gli-1 siRNA and 5-fluorouracil (5-Fu).

RESULTS: Inhibition of Gli-1 mRNA in Huh7 cells through Gli-1 siRNA reduced cell viability. Gli-1 siRNA treatment also induced apoptosis by three criteria, increase in the sub-G1 cell cycle fraction, nuclear condensation, a morphologic change typical of apoptosis, and activation of caspase-3. Gli-1 siRNA was also able to down-regulate Bcl-2. However, Gli-1 siRNA resulted in no significant changes in Bcl-xl, Bax, Bad, and Bid. Furthermore, Gli-1 siRNA increased the cytotoxic effect of 5-Fu on Huh7 cell.

CONCLUSION: Down-regulation of Bcl-2 plays an important role in apoptosis induced by Gli-1 siRNA in HCC cells. Combination Gli-1 siRNA with chemotherapeutic drug could represent a more promising strategy against HCC. The effects of the strategies need further investigation

in vivo and may have potential clinical application.