Smoothened variants explain the majority of drug resistance in Basal cell carcinoma.
2015; 27 (3): 342-53
Advanced basal cell carcinomas (BCCs) frequently acquire resistance to Smoothened (SMO) inhibitors through unknown mechanisms. Here we identify SMO mutations in 50% (22 of 44) of resistant BCCs and show that these mutations maintain Hedgehog signaling in the presence of SMO inhibitors. Alterations include four ligand binding pocket mutations defining sites of inhibitor binding and four variants conferring constitutive activity and inhibitor resistance, illuminating pivotal residues that ensure receptor autoinhibition. In the presence of a SMO inhibitor, tumor cells containing either class of SMO mutants effectively outcompete cells containing the wild-type SMO. Finally, we show that both classes of SMO variants respond to aPKC-ι/λ or GLI2 inhibitors that operate downstream of SMO, setting the stage for the clinical use of GLI antagonists.
View details for DOI 10.1016/j.ccell.2015.02.002
View details for PubMedID 25759020
Epigenetic targeting of Hedgehog pathway transcriptional output through BET bromodomain inhibition.
2014; 20 (7): 732-740
Hedgehog signaling drives oncogenesis in several cancers, and strategies targeting this pathway have been developed, most notably through inhibition of Smoothened (SMO). However, resistance to Smoothened inhibitors occurs by genetic changes of Smoothened or other downstream Hedgehog components. Here we overcome these resistance mechanisms by modulating GLI transcription through inhibition of bromo and extra C-terminal (BET) bromodomain proteins. We show that BRD4 and other BET bromodomain proteins regulate GLI transcription downstream of SMO and suppressor of fused (SUFU), and chromatin immunoprecipitation studies reveal that BRD4 directly occupies GLI1 and GLI2 promoters, with a substantial decrease in engagement of these sites after treatment with JQ1, a small-molecule inhibitor targeting BRD4. Globally, genes associated with medulloblastoma-specific GLI1 binding sites are downregulated in response to JQ1 treatment, supporting direct regulation of GLI activity by BRD4. Notably, patient- and GEMM (genetically engineered mouse model)-derived Hedgehog-driven tumors (basal cell carcinoma, medulloblastoma and atypical teratoid rhabdoid tumor) respond to JQ1 even when harboring genetic lesions rendering them resistant to Smoothened antagonists. Altogether, our results reveal BET proteins as critical regulators of Hedgehog pathway transcriptional output and nominate BET bromodomain inhibitors as a strategy for treating Hedgehog-driven tumors with emerged or a priori resistance to Smoothened antagonists.
View details for DOI 10.1038/nm.3613
View details for PubMedID 24973920
Advanced treatment for basal cell carcinomas.
Cold Spring Harbor perspectives in medicine
2014; 4 (7)
Basal cell carcinomas (BCCs) are very common epithelial cancers that depend on the Hedgehog pathway for tumor growth. Traditional therapies such as surgical excision are effective for most patients with sporadic BCC; however, better treatment options are needed for cosmetically sensitive or advanced and metastatic BCC. The first approved Hedgehog antagonist targeting the membrane receptor Smoothened, vismodegib, shows remarkable effectiveness on both syndromic and nonsyndromic BCCs. However, drug-resistant tumors frequently develop, illustrating the need for the development of next-generation Hedgehog antagonists targeting pathway components downstream from Smoothened. In this article, we will summarize available BCC treatment options and discuss the development of next-generation antagonists.
View details for DOI 10.1101/cshperspect.a013581
View details for PubMedID 24985127
Identification of Genes Promoting Skin Youthfulness by Genome-Wide Association Study
JOURNAL OF INVESTIGATIVE DERMATOLOGY
2014; 134 (3): 651-657
To identify genes that promote facial skin youthfulness (SY), a genome-wide association study on an Ashkenazi Jewish discovery group (n=428) was performed using Affymetrix 6.0 Single-Nucleotide Polymorphism (SNP) Array. After SNP quality controls, 901,470 SNPs remained for analysis. The eigenstrat method showed no stratification. Cases and controls were identified by global facial skin aging severity including intrinsic and extrinsic parameters. Linear regression adjusted for age and gender, with no significant differences in smoking history, body mass index, menopausal status, or personal or family history of centenarians. Six SNPs met the Bonferroni threshold with Pallele<10(-8); two of these six had Pgenotype<10(-8). Quantitative trait loci mapping confirmed linkage disequilibrium. The six SNPs were interrogated by MassARRAY in a replication group (n=436) with confirmation of rs6975107, an intronic region of KCND2 (potassium voltage-gated channel, Shal-related family member 2) (Pgenotype=0.023). A second replication group (n=371) confirmed rs318125, downstream of DIAPH2 (diaphanous homolog 2 (Drosophila)) (Pallele=0.010, Pgenotype=0.002) and rs7616661, downstream of EDEM1 (ER degradation enhancer, mannosidase α-like 1) (Pgenotype=0.042). DIAPH2 has been associated with premature ovarian insufficiency, an aging phenotype in humans. EDEM1 associates with lifespan in animal models, although not humans. KCND2 is expressed in human skin, but has not been associated with aging. These genes represent new candidate genes to study the molecular basis of healthy skin aging.
View details for DOI 10.1038/jid.2013.381
View details for Web of Science ID 000331669800013
View details for PubMedID 24037343
"Atypical" regulation of Hedgehog-dependent cancers.
2014; 25 (2): 133-134
Growing evidence indicates targeting PKCι may be effective in treating Hedgehog-dependent cancers. In this issue of Cancer Cell, Justilien and colleagues present the surprising finding that PKCι promotes Hedgehog ligand production and lung squamous cell carcinoma growth through SOX2, rather than the canonical transcription factor GLI.
View details for DOI 10.1016/j.ccr.2014.01.027
View details for PubMedID 24525228
- Surgical excision after neoadjuvant therapy with vismodegib for a locally advanced Basal cell carcinoma and resistant Basal carcinomas in gorlin syndrome. JAMA dermatology (Chicago, Ill.) 2013; 149 (5): 639-641
"Patch"ing up our tumor signaling knowledge.
journal of investigative dermatology
2013; 133 (5): 1131-1133
The tumor suppressor Patched1 (Ptch1) possesses well-described roles in regulating sonic hedgehog (SHH) signaling in the skin and preventing the formation of basal cell carcinomas (BCCs). In this issue, Kang et al. extend their previous work to show that a naturally occurring allele of Ptch1 found in FVB mice promotes early squamous cell carcinoma (SCC) growth without aberrant activation of the SHH pathway. The study reveals new roles for Ptch1 that lie at the nexus between BCC and SCC formation.
View details for DOI 10.1038/jid.2012.506
View details for PubMedID 23594533
GLI activation by atypical protein kinase C ?/? regulates the growth of basal cell carcinomas.
2013; 494 (7438): 484-488
Growth of basal cell carcinomas (BCCs) requires high levels of hedgehog (HH) signalling through the transcription factor GLI. Although inhibitors of membrane protein smoothened (SMO) effectively suppress HH signalling, early tumour resistance illustrates the need for additional downstream targets for therapy. Here we identify atypical protein kinase C ι/λ (aPKC-ι/λ) as a novel GLI regulator in mammals. aPKC-ι/λ and its polarity signalling partners co-localize at the centrosome and form a complex with missing-in-metastasis (MIM), a scaffolding protein that potentiates HH signalling. Genetic or pharmacological loss of aPKC-ι/λ function blocks HH signalling and proliferation of BCC cells. Prkci is a HH target gene that forms a positive feedback loop with GLI and exists at increased levels in BCCs. Genome-wide transcriptional profiling shows that aPKC-ι/λ and SMO control the expression of similar genes in tumour cells. aPKC-ι/λ functions downstream of SMO to phosphorylate and activate GLI1, resulting in maximal DNA binding and transcriptional activation. Activated aPKC-ι/λ is upregulated in SMO-inhibitor-resistant tumours and targeting aPKC-ι/λ suppresses signalling and growth of resistant BCC cell lines. These results demonstrate that aPKC-ι/λ is critical for HH-dependent processes and implicates aPKC-ι/λ as a new, tumour-selective therapeutic target for the treatment of SMO-inhibitor-resistant cancers.
View details for DOI 10.1038/nature11889
View details for PubMedID 23446420
- Rapid Genetic Analysis of Epithelial-Mesenchymal Signaling During Hair Regeneration JOVE-JOURNAL OF VISUALIZED EXPERIMENTS 2013
Rapid genetic analysis of epithelial-mesenchymal signaling during hair regeneration.
Journal of visualized experiments : JoVE
Hair follicle morphogenesis, a complex process requiring interaction between epithelia-derived keratinocytes and the underlying mesenchyme, is an attractive model system to study organ development and tissue-specific signaling. Although hair follicle development is genetically tractable, fast and reproducible analysis of factors essential for this process remains a challenge. Here we describe a procedure to generate targeted overexpression or shRNA-mediated knockdown of factors using lentivirus in a tissue-specific manner. Using a modified version of a hair regeneration model, we can achieve robust gain- or loss-of-function analysis in primary mouse keratinocytes or dermal cells to facilitate study of epithelial-mesenchymal signaling pathways that lead to hair follicle morphogenesis. We describe how to isolate fresh primary mouse keratinocytes and dermal cells, which contain dermal papilla cells and their precursors, deliver lentivirus containing either shRNA or cDNA to one of the cell populations, and combine the cells to generate fully formed hair follicles on the backs of nude mice. This approach allows analysis of tissue-specific factors required to generate hair follicles within three weeks and provides a fast and convenient companion to existing genetic models.
View details for DOI 10.3791/4344
View details for PubMedID 23486463
- Hedgehog pathway inhibition and the race against tumor evolution JOURNAL OF CELL BIOLOGY 2013: 45-49
Hedgehog pathway inhibition and the race against tumor evolution
JOURNAL OF CELL BIOLOGY
2012; 199 (2): 193-197
Dependence of basal cell carcinomas and medulloblastomas on the Hedgehog pathway provides an opportunity for targeted or "personalized" therapy. The recent effectiveness and FDA approval of the first Smoothened inhibitors validates this class of agents, but has revealed drug-resistant tumor variants that bypass Smoothened inhibition. Here, we summarize the effectiveness of Hedgehog pathway inhibitors and highlight promising areas for the development of next generation drug antagonists for Hedgehog-dependent cancers.
View details for DOI 10.1083/jcb.201207140
View details for Web of Science ID 000309982400002
View details for PubMedID 23071148
Partitioning-defective Protein 6 (Par-6) Activates Atypical Protein Kinase C (aPKC) by Pseudosubstrate Displacement
JOURNAL OF BIOLOGICAL CHEMISTRY
2012; 287 (25): 21003-21011
Atypical protein kinase C (aPKC) controls cell polarity by modulating substrate cortical localization. Aberrant aPKC activity disrupts polarity, yet the mechanisms that control aPKC remain poorly understood. We used a reconstituted system with purified components and a cultured cell cortical displacement assay to investigate aPKC regulation. We find that aPKC is autoinhibited by two domains within its NH(2)-terminal regulatory half, a pseudosubstrate motif that occupies the kinase active site, and a C1 domain that assists in this process. The Par complex member Par-6, previously thought to inhibit aPKC, is a potent activator of aPKC in our assays. Par-6 and aPKC interact via PB1 domain heterodimerization, and this interaction activates aPKC by displacing the pseudosubstrate, although full activity requires the Par-6 CRIB-PDZ domains. We propose that, along with its previously described roles in controlling aPKC localization, Par-6 allosterically activates aPKC to allow for high spatial and temporal control of substrate phosphorylation and polarization.
View details for DOI 10.1074/jbc.M112.360495
View details for Web of Science ID 000306416800022
View details for PubMedID 22544755
MIM and Cortactin Antagonism Regulates Ciliogenesis and Hedgehog Signaling
2010; 19 (2): 270-283
The primary cilium is critical for transducing Sonic hedgehog (Shh) signaling, but the mechanisms of its transient assembly are poorly understood. Previously we showed that the actin regulatory protein Missing-in-Metastasis (MIM) regulates Shh signaling, but the nature of MIM's role was unknown. Here we show that MIM is required at the basal body of mesenchymal cells for cilia maintenance, Shh responsiveness, and de novo hair follicle formation. MIM knockdown results in increased Src kinase activity and subsequent hyperphosphorylation of the actin regulator Cortactin. Importantly, inhibition of Src or depletion of Cortactin compensates for the cilia defect in MIM knockdown cells, whereas overexpression of Src or phospho-mimetic Cortactin is sufficient to inhibit ciliogenesis. Our results suggest that MIM promotes ciliogenesis by antagonizing Src-dependent phosphorylation of Cortactin and describe a mechanism linking regulation of the actin cytoskeleton with ciliogenesis and Shh signaling during tissue regeneration.
View details for DOI 10.1016/j.devcel.2010.07.009
View details for Web of Science ID 000281090000012
View details for PubMedID 20708589
aPKC Phosphorylates Miranda to Polarize Fate Determinants during Neuroblast Asymmetric Cell Division
2009; 19 (9): 723-729
Asymmetric cell divisions generate daughter cells with distinct fates by polarizing fate determinants into separate cortical domains. Atypical protein kinase C (aPKC) is an evolutionarily conserved regulator of cell polarity. In Drosophila neuroblasts, apically restricted aPKC is required for segregation of neuronal differentiation factors such as Numb and Miranda to the basal cortical domain. Whereas Numb is polarized by direct aPKC phosphorylation, Miranda asymmetry is thought to occur via a complicated cascade of repressive interactions (aPKC -| Lgl -| myosin II -| Miranda).Here we provide biochemical, cellular, and genetic data showing that aPKC directly phosphorylates Miranda to exclude it from the cortex and that Lgl antagonizes this activity. Miranda is phosphorylated by aPKC at several sites in its cortical localization domain and phosphorylation is necessary and sufficient for cortical displacement, suggesting that the repressive-cascade model is incorrect. In investigating key results that led to this model, we found that Y-27632, a Rho kinase inhibitor used to implicate myosin II, efficiently inhibits aPKC. Lgl3A, a nonphosphorylatable Lgl variant used to implicate Lgl in this process, inhibits the formation of apical aPKC crescents in neuroblasts. Furthermore, Lgl directly inhibits aPKC kinase activity.Miranda polarization during neuroblast asymmetric cell division occurs by displacement from the apical cortex by direct aPKC phosphorylation. Rather than mediating Miranda cortical displacement, Lgl instead promotes aPKC asymmetry by regulating its activity. The role of myosin II in neuroblast polarization, if any, is unknown.
View details for DOI 10.1016/j.cub.2009.03.056
View details for Web of Science ID 000266131800022
View details for PubMedID 19375318
Cdc42 acts downstream of Bazooka to regulate neuroblast polarity through Par-6-aPKC
JOURNAL OF CELL SCIENCE
2007; 120 (18): 3200-3206
Cdc42 recruits Par-6-aPKC to establish cell polarity from worms to mammals. Although Cdc42 is reported to have no function in Drosophila neuroblasts, a model for cell polarity and asymmetric cell division, we show that Cdc42 colocalizes with Par-6-aPKC at the apical cortex in a Bazooka-dependent manner, and is required for Par-6-aPKC localization. Loss of Cdc42 disrupts neuroblast polarity: cdc42 mutant neuroblasts have cytoplasmic Par-6-aPKC, and this phenotype is mimicked by neuroblast-specific expression of a dominant-negative Cdc42 protein or a Par-6 protein that lacks Cdc42-binding ability. Conversely, expression of constitutively active Cdc42 leads to ectopic Par-6-aPKC localization and corresponding cell polarity defects. Bazooka remains apically enriched in cdc42 mutants. Robust Cdc42 localization requires Par-6, indicating the presence of feedback in this pathway. In addition to regulating Par-6-aPKC localization, Cdc42 increases aPKC activity by relieving Par-6 inhibition. We conclude that Cdc42 regulates aPKC localization and activity downstream of Bazooka, thereby directing neuroblast cell polarity and asymmetric cell division.
View details for DOI 10.1242/jcs.014902
View details for Web of Science ID 000249559400006
View details for PubMedID 17726059