SMO Levels Research Articles

Arih2 regulates Hedgehog signaling through smoothened ubiquitylation and ER-associated degradation.

During Hedgehog signaling, the ciliary levels of Ptch1 and Smo are regulated by the pathway. At the basal state, Ptch1 localizes to cilia and prevents the ciliary accumulation and activation of Smo. Upon binding a Hedgehog ligand, Ptch1 exits cilia, relieving inhibition of Smo. Smo then concentrates in cilia, becomes activated and activates downstream signaling. Loss of the ubiquitin E3 ligase Arih2 elevates basal Hedgehog signaling, elevates the cellular level of Smo and increases basal levels of ciliary Smo. Mice express two isoforms of Arih2 with Arih2α found primarily in the nucleus and Arih2β found on the cytoplasmic face of the endoplasmic reticulum (ER). Re-expression of ER-localized Arih2β but not nuclear-localized Arih2α rescues the Arih2 mutant phenotypes. When Arih2 is defective, protein aggregates accumulate in the ER and the unfolded protein response is activated. Arih2β appears to regulate the ER-associated degradation (ERAD) of Smo preventing excess and potentially misfolded Smo from reaching the cilium and interfering with pathway regulation.

E3 ubiquitin ligase Wwp1 regulates ciliary dynamics of the Hedgehog receptor Smoothened.

The Hedgehog pathway, critical to vertebrate development, is organized in primary cilia. Activation of signaling causes the Hedgehog receptor Ptch1 to exit cilia, allowing a second receptor, Smo, to accumulate in cilia and activate the downstream steps of the pathway. Mechanisms regulating the dynamics of these receptors are unknown, but the ubiquitination of Smo regulates its interaction with the intraflagellar transport system to control ciliary levels. A focused screen of ubiquitin-related genes identified nine required for maintaining low ciliary Smo at the basal state. These included cytoplasmic E3s (Arih2, Mgrn1, and Maea), a ciliary localized E3 (Wwp1), a ciliary localized E2 (Ube2l3), a deubiquitinase (Bap1), and three adaptors (Kctd5, Skp1a, and Skp2). The ciliary E3, Wwp1, binds Ptch1 and localizes to cilia at the basal state. Activation of signaling removes both Ptch1 and Wwp1 from cilia, thus providing an elegant mechanism for Ptch1 to regulate ciliary Smo levels.

NCTD Retards AML HL60 Cell Proliferation via Targeting Hedgehog/SOX2 axis

To investigate the effect of norcantharidin (NCTD) to proliferation of leukemia cells through disrupting key regulators of sonic Hedgehog (SHH) pathway and its downstream transcription factor SOX2. CCK8 was used to detected the HL60 and NB4 cells after inhibited by NCTD, SMO and GLI1 inhibitor for 24 hours. Expression level of SMO, GLI1 and SOX2 in HL60 cells with NCTD treatment was detected by immunoblot. HL60 cells were transfected with pcDNA3.1 plasmid expressing GLI1 or SOX2. Empty vector and pcDNA3. 1-EGFP were divided into negative and positive control group, respectively. The expression of exogenous GLI1 or SOX2 in HL60 cells was confirmed by immunoblot, and growth curve of HL60 cell was checked by CCK8. Proliferation of genetic modified HL60 cells treated by various dose of NCTD was detected. NCTD, SMO/GLI1 inhibitors could inhibit the proliferation of NB4 and HL60 cells in a dose-dependent manner. Compared with solvent (DMSO)-treated control group, NCTD remarkably decreased protein level of SMO, GLI1 and SOX2. GLI1 and SOX2 were overexpressed in HL60 cells as compared with pcDNA3.1 empty vector-transfected group. Growth curve demonstrated significant proliferative advantage of GLI1/SOX2-transfected cells. CCK8 assay indicated that GLI1/SOX2-overexpressed HL60 cells were more resistant to NCTD treatment. NCTD attenuates HL60 proliferation via targeting the Hedgehog/SOX2 axis.

Hypoxia induced Sonic Hedgehog signaling regulates cancer stemness, epithelial-to-mesenchymal transition and invasion in cholangiocarcinoma

Aberrant activation of Sonic Hedgehog (SHH) pathway has been implicated in a variety of cancers including cholangiocarcinoma (CC); however, the influencing factors are still unknown. Additionally, intratumoral hypoxia is known to contribute towards therapeutic resistance through modulatory effects on various pathways. In this study, we investigated the relationship between hypoxia and SHH pathway activation and the effect of this interplay on cancer stemness and epithelial-to- mesenchymal transition (EMT) during cholangiocarcinogenesis. Hypoxia promoted SHH pathway activation, evidenced by upregulated SHH and SMO levels, and enhanced glioma-associated oncogene homolog 1 (GLI1) nuclear translocation; whereas silencing of HIF-1α impaired SHH upregulation. Hypoxia also enhanced the expression of cancer stem cell (CSC) transcription factors (NANOG, Oct4, SOX2), CD133 and EMT markers (N-cadherin, Vimentin), thereby supporting invasion. Cyclopamine treatment suppressed hypoxia induced SHH pathway activation, consequently reducing invasiveness by downregulating the expression of CSC transcription factors, CD133 and EMT. Cyclopamine induced apoptosis in CC cells under hypoxia, suggesting that hypoxia induced activation of SHH pathway has modulatory effects on CC progression. Therefore, SHH signaling is proposed as a target for CC treatment, which is refractory to standard chemotherapy.

A Smo/Gli Multitarget Hedgehog Pathway Inhibitor Impairs Tumor Growth.

Pharmacological Hedgehog (Hh) pathway inhibition has emerged as a valuable anticancer strategy. A number of small molecules able to block the pathway at the upstream receptor Smoothened (Smo) or the downstream effector glioma-associated oncogene 1 (Gli1) has been designed and developed. In a recent study, we exploited the high versatility of the natural isoflavone scaffold for targeting the Hh signaling pathway at multiple levels showing that the simultaneous targeting of Smo and Gli1 provided synergistic Hh pathway inhibition stronger than single administration. This approach seems to effectively overcome the drug resistance, particularly at the level of Smo. Here, we combined the pharmacophores targeting Smo and Gli1 into a single and individual isoflavone, compound 22, which inhibits the Hh pathway at both upstream and downstream level. We demonstrate that this multitarget agent suppresses medulloblastoma growth in vitro and in vivo through antagonism of Smo and Gli1, which is a novel mechanism of action in Hh inhibition.

Hedgehog Pathway Inhibition for the Treatment of Basal Cell Carcinoma.

Globally, basal cell carcinoma is the most commonly diagnosed cancer. While most cases are amenable to surgery, treatment options for advanced basal cell carcinoma, including locally advanced basal cell carcinoma and metastatic basal cell carcinoma, have proved more difficult. Recent advances regarding the role of hedgehog signaling in the pathogenesis of basal cell carcinoma and the identification of hedgehog pathway inhibitors have facilitated the development of treatment options with improved clinical outcomes. The hedgehog signaling pathway regulates development, cell proliferation, and tissue repair. The pathway is tightly regulated under normal physiological conditions. However, dysregulated hedgehog signaling in human cancers was first described in patients with basal cell carcinoma nevus syndrome and sporadic basal cell carcinoma, in which germline or somatic mutations in pathway components (e.g., smoothened [Smo] and patched-1) lead to constant activation. Subsequently, inhibitors blocking hedgehog signaling either at the level of Smo (i.e., vismodegib, sonidegib, patidegib, and itraconazole) or via an unknown mode of action (arsenic trioxide) were identified. The hedgehog inhibitor vismodegib is approved for the treatment of locally advanced basal cell carcinoma and metastatic basal cell carcinoma while sonidegib is approved for the treatment of locally advanced basal cell carcinoma in the USA and Europe; and for locally advanced basal cell carcinoma and metastatic basal cell carcinoma in Switzerland and Australia. The most common treatment-emergent adverse events associated with approved hedgehog inhibitors include muscle spasms, dysgeusia, and alopecia. This review addresses the challenges associated with appropriately diagnosing locally advanced basal cell carcinoma, provides an overview of hedgehog signaling in basal cell carcinoma, and discusses the pharmacology of hedgehog inhibitors and their efficacy, and adverse events associated with hedgehog inhibitor use, and their management.

Abstract 1150: Downregulation of Hedgehog signaling via Sirt6 activation is important to docosahexaenoic acid-induced cell death in human EGFR mutant non-small cell lung cancer

Abstract Docosahexaenoic acid (DHA) induces apoptotic cell death through several mechanisms in cancer cells. Here we report that DHA-induced apoptotic cell death is related to the inhibition of Hedgehog signaling via SIRT6 activation in human PC9 and H1975 nonsmall cell lung cancer (NSCLC). DHA-induced cell death was confirmed increase of the protein levels of cleaved PARP and caspase-3 Bax as well as the number of TUNEL positive cells and the Sub-G1 proportion in PC9 and H1975. DHA significantly increased the SIRT6 levels. Knockdown of SIRT6 by siRNAs inhibited apoptosis induced by DHA, while SIRT6 overexpression increased apoptotic cell death, indicating that DHA-induced SIRT6 activation results in apoptosis. In addition, SIRT6 activation by DHA treatment was associated with downregulation of Hh signaling and knockdown of SIRT6 resulted in augmentation of Hh signaling, suggesting elevation of SIRT6 levels in DHA-treated NSCLC cells leads to downregulate the Hh signaling. Smo activator SAG increased the protein levels of Hh signaling molecules by DHA, and SAG plus DHA treatment decreased cleaved PARP levels, implying that DHA-inhibited Hh signaling is related to apoptotic cell death. To unveil the effects of endogenous DHA on apoptosis via SIRT6-mediated Hh signaling downregulation, we used PC9 stable cell lines of fat-1 (ω3-desaturase) gene. The SIRT6 levels were significantly increased and Hh signaling molecules were diminished in fat-1 stable PC9 (f-PC9) cells, compared with the cells transfected with the control vector (c-PC9). Moreover, SIRT6 expression was elevated and Gli and smo levels were inhibited in tumor tissues from f-PC9 cells-injected mice, demonstrating that DHA regulates SIRT6 and Hh signaling in vivo. Taken together, these results suggest that DHA may induce apoptotic cell death through SIRT6-modulated Hh signaling suppression in human NSCLC cells. These findings implicate that ω3-PUFAs may represent a potential effective therapy for the chemoprevention and treatment of human NSCLC. [This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2007-0054932, NRF-2015R1D1A1A01056887) and by the framework of international cooperation program managed by National Research Foundation of Korea (2015K2A2A6002008)]. Citation Format: Soyeon Jeong, Kaipeng Jing, Soyeon Shin, Seung-Hyeon Han, Yoon-Seon Yoo, Prashanta Silwal, Young-Joo Jeon, Jun-Young Heo, Gi-Ryang Kweon, Seung-Kiel Park, Jong-Il Park, Tong Wu, Kyu Lim. Downregulation of Hedgehog signaling via Sirt6 activation is important to docosahexaenoic acid-induced cell death in human EGFR mutant non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1150. doi:10.1158/1538-7445.AM2017-1150

The hedgehog inhibitor GANT61 sensitizes prostate cancer cells to ionizing radiation both in vitro and in vivo.

Limited data exists regarding the combination of Hedgehog signaling (Hh) inhibition and radiotherapy, even though there are several indications that this might be a promising treatment strategy. In this study, we evaluated the combination of two Hh inhibitors, the SMO inhibitor GDC-0449 and the GLI inhibitor GANT61 with radiotherapy in different prostate cancer (PCa) models. In vitro, GANT61 was able to sensitize 22Rv1 PCa cells but not PC3 and DU145 PCa cells. The lack of radiosensitization in the latter cell lines was shown to be dependent on the presence of mutated p53. Introduction of WT p53 into PC3 cells resulted in radiosensization following GANT61 treatment, suggesting that the p53 transcription factor plays an important role in the GANT61-induced radiosensitization in vitro. Targeting at the level of SMO (GDC-0449) did not show cytotoxicity or synergy with radiation. Furthermore, we confirmed the radiosensitization effect of GANT61 in two in vivo xenograft PCa models. The decrease in tumor growth was associated with decreased proliferation and increased apoptosis. In conclusion, we provide evidence that GANT61 in combination with radiation treatment might represent a promising therapeutic strategy for enhancing the radiation response of PCa patients.

A Functional and Putative Physiological Role of Calcitriol in Patched1/Smoothened Interaction

The Patched1 (Ptch)-mediated inhibition of Smoothened (Smo) is still an open question. However, a direct Ptch/Smo interaction has been excluded, Smo modulators were identified, but the endogenous signal transmitting molecule remains undiscovered. Here, we demonstrate that calcitriol, the hormonally active form of vitamin D3, is an excellent candidate for transmission of Ptch/Smo interaction. Our study reveals that Ptch expression is sufficient to release calcitriol from the cell and that calcitriol inhibits Smo action and ciliary translocation by acting on a site distinct from the 7-transmembrane domain or the cysteine-rich domain. Moreover calcitriol strongly synergizes with itraconazole (ITZ) in Smo inhibition, which did not result from elevated calcitriol bioavailability due to ITZ-mediated 24-hydroxylase inhibition but rather from a direct interaction of the compounds at the level of Smo. Together, we suggest that calcitriol represents a possible endogenous transmitter of Ptch/Smo interaction. Moreover calcitriol or calcitriol derivatives combined with ITZ might be a treatment option of Hedgehog-associated cancers.

Switch of PKA substrates from Cubitus interruptus to Smoothened in the Hedgehog signalosome complex

Hedgehog (Hh) signalling is crucial for developmental patterning and tissue homeostasis. In Drosophila, Hh signalling is mediated by a bifunctional transcriptional mediator, called Cubitus interruptus (Ci). Protein Kinase A (PKA)-dependent phosphorylation of the serpentine protein Smoothened (Smo) leads to Ci activation, whereas PKA-dependent phosphorylation of Ci leads to the formation of Ci repressor form. The mechanism that switches PKA from an activator to a repressor is not known. Here we show that Hh signalling activation causes PKA to switch its substrates from Ci to Smo within the Hh signalling complex (HSC). In particular, Hh signalling increases the level of Smo, which then outcompetes Ci for association with PKA and causes a switch in PKA substrate recognition. We propose a new model in which the PKA is constitutively present and active within the HSC, and in which the relative levels of Ci and Smo within the HSC determine differential activation and cellular response to Hh signalling.

Antitumoral Effects of Calcitriol in Basal Cell Carcinomas Involve Inhibition of Hedgehog Signaling and Induction of Vitamin D Receptor Signaling and Differentiation

Activation of the Hedgehog (Hh)-signaling pathway due to deficiency in the Hh receptor Patched1 (Ptch) is the pivotal defect leading to formation of basal cell carcinoma (BCC). Recent reports provided evidence of Ptch-dependent secretion of vitamin D(3)-related compound, which functions as an endogenous inhibitor of Hh signaling by repressing the activity of the signal transduction partner of Ptch, Smoothened (Smo). This suggests that Ptch-deficient tumor cells are devoid of this substance, which in turn results in activation of Hh-signaling. Here, we show that the application of the physiologically active form of vitamin D(3), calcitriol, inhibits proliferation and growth of BCC of Ptch mutant mice in vitro and in vivo. This is accompanied by the activation of the vitamin D receptor (Vdr) and induction of BCC differentiation. In addition, calcitriol inhibits Hh signaling at the level of Smo in a Vdr-independent manner. The concomitant antiproliferative effects on BCC growth are stronger than those of the Hh-specific inhibitor cyclopamine, even though the latter more efficiently inhibits Hh signaling. Taken together, we show that exogenous supply of calcitriol controls the activity of 2 independent pathways, Hh and Vdr signaling, which are relevant to tumorigenesis and tumor treatment. These data suggest that calcitriol could be a therapeutic option in the treatment of BCC, the most common tumor in humans.

Casein Kinase 2 Promotes Hedgehog Signaling by Regulating both Smoothened and Cubitus Interruptus

Casein kinase 2 (CK2) is a typical serine/threonine kinase consisting of α and β subunits and has been implicated in many cellular and developmental processes. In this study, we demonstrate that CK2 is a positive regulator of the Hedgehog (Hh) signal transduction pathway. We found that inactivation of CK2 by CK2β RNAi enhances the loss-of-Hh wing phenotype induced by a dominant negative form of Smoothened (Smo). CK2β RNAi attenuates Hh-induced Smo accumulation and down-regulates Hh target gene expression, whereas increasing CK2 activity by coexpressing CK2α and CK2β increases Smo accumulation and induces ectopic Hh target gene expression. We identified the serine residues in Smo that can be phosphorylated by CK2 in vitro. Mutating these serine residues attenuates the ability of Smo to transduce high level Hh signaling activity in vivo. Furthermore, we found that CK2 plays an additional positive role downstream of Smo by regulating the stability of full-length Cubitus interruptus (Ci). CK2β RNAi promotes Ci degradation whereas coexpressing CK2α and CK2β increases the half-life of Ci. We showed that CK2 prevents Ci ubiquitination and degradation by the proteasome. Thus, CK2 promotes Hh signaling activity by regulating multiple pathway components.

Patched regulates Smoothened trafficking using lipoprotein-derived lipids

Hedgehog (Hh) is a lipoprotein-borne ligand that regulates both patterning and proliferation in a wide variety of vertebrate and invertebrate tissues. When Hh is absent, its receptor Patched (Ptc) represses Smoothened (Smo) signaling by an unknown catalytic mechanism that correlates with reduced Smo levels on the basolateral membrane. Ptc contains a sterol-sensing domain and is similar to the Niemann-Pick type C-1 protein, suggesting that Ptc might regulate lipid trafficking to repress Smo. However, no endogenous lipid regulators of Smo have yet been identified, nor has it ever been shown that Ptc actually controls lipid trafficking. Here, we show that Drosophila Ptc recruits internalized lipoproteins to Ptc-positive endosomes and that its sterol-sensing domain regulates trafficking of both lipids and Smo from this compartment. Ptc utilizes lipids derived from lipoproteins to destabilize Smo on the basolateral membrane. We propose that Ptc normally regulates Smo degradation by changing the lipid composition of endosomes through which Smo passes, and that the presence of Hh on lipoproteins inhibits utilization of their lipids by Ptc.

Tow (Target of Wingless), a novel repressor of the Hedgehog pathway in Drosophila

Hedgehog (Hh) signalling plays a crucial role in the development and patterning of many tissues in both vertebrates and invertebrates. Aberrations in this pathway lead to severe developmental defects and cancer. Hh signal transduction in receiving cells is a well studied phenomenon; however questions still remain concerning the mechanism of repression of the pathway activator Smoothened (Smo) in the absence of Hh. Here we describe a novel repressor of the Hh pathway, Target of Wingless (Tow). Tow represents the Drosophila homolog of a conserved uncharacterised protein family. We show that Tow acts in Hh receiving cells, where its overexpression represses all levels of Hh signalling, and that this repression occurs upstream or at the level of Smo and downstream of the Hh receptor Patched (Ptc). In addition, we find that like Ptc, overexpression of Tow causes an accumulation of lipophorin in the wing disc. We demonstrate that loss of tow enhances different ptc alleles in a similar manner to another pathway repressor, Suppressor of Fused (SuFu), possibly through mediating Ptc dependant lipophorin internalisation. Combined, these results demonstrate that Tow is an important novel regulator of the Hh pathway in the wing imaginal disc, and may shed light on the mechanism of Ptc repression of Smo.

S1225 Fecal Osteoprotegerin: A Marker for Pediatric Ulcerative Colitis At Diagnosis - a Pilot Study

SMO levels in involved UC rectal tissues versus uninvolved right colon in a group of patients with left-sided colitis. There was an increase in SMO levels from 0.75 ± 0.21 to 2.63 ± 0.94 x 1019 copies, which represented a 3.5-fold increase (n = 10, p = 0.006 by paired t test). Conclusions: In general, SMO mRNA expression is increased in UC tissues. The increase was more marked in tissues with quiescent or mild colitis than in tissues from moderate or severe colitis. This pattern suggests that like ODC, SMO expression and polyamine metabolism also vary depending on disease activity. Assessment of SMO levels is important in understanding dysregulated polyamine homeostasis in UC and may prove useful as a marker of early or mild UC.

The role of kinases in the Hedgehog signalling pathway

The Hedgehog (Hh) signalling pathway has a crucial role in several developmental processes and is aberrantly activated in a variety of cancers. In Drosophila, many of the canonical Hh pathway components are phosphorylated, yet the precise role of these phosphorylation events in the regulation of Hh signal transduction is unclear. Furthermore, the Hh pathway receives input from several kinases that have well-described roles in other cellular functions, some of which have both positive and negative effects on Hh signalling. Several recent studies have characterized the role of specific phosphorylation events in the Hh pathway, and have begun to shed light on how phosphorylation of Hh signalling components affects their subcellular location, stability and activity to mediate the transcriptional response to the Hh gradient.