Noncanonical hedgehog pathway activation through SRF-MKL1 promotes drug resistance in basal cell carcinomas.
2018; 24 (3): 271–81
Soil Primes the Seed: Epigenetic Landscape Drives Tumor Behavior.
Cell stem cell
2017; 20 (2): 149-150
Hedgehog pathway-dependent cancers can escape Smoothened (SMO) inhibition through mutations in genes encoding canonical hedgehog pathway components; however, around 50% of drug-resistant basal cell carcinomas (BCCs) lack additional variants of these genes. Here we use multidimensional genomics analysis of human and mouse drug-resistant BCCs to identify a noncanonical hedgehog activation pathway driven by the transcription factor serum response factor (SRF). Active SRF along with its coactivator megakaryoblastic leukemia 1 (MKL1) binds DNA near hedgehog target genes and forms a previously unknown protein complex with the hedgehog transcription factor glioma-associated oncogene family zinc finger-1 (GLI1), causing amplification of GLI1 transcriptional activity. We show that cytoskeletal activation through Rho and the formin family member Diaphanous (mDia) is required for SRF-MKL-driven GLI1 activation and for tumor cell viability. Remarkably, nuclear MKL1 staining served as a biomarker in tumors from mice and human subjects to predict tumor responsiveness to MKL inhibitors, highlighting the therapeutic potential of targeting this pathway. Thus, our study illuminates, for the first time, cytoskeletal-activation-driven transcription as a personalized therapeutic target for combatting drug-resistant malignancies.
View details for DOI 10.1038/nm.4476
View details for PubMedID 29400712
View details for PubMedCentralID PMC5839965
Tumor-Derived Suppressor of Fused Mutations Reveal Hedgehog Pathway Interactions
2016; 11 (12)
Whether invasive tumor phenotypes like EMT arise from oncogenic drivers or from priming of the pre-tumor cell of origin remains unknown. In this issue of Cell Stem Cell, Latil et al. (2017) show that the pre-tumor niche establishes a chromatin state predisposing squamous cell carcinomas to undergo EMT and metastasis, suggesting that the pre-tumor epigenome has prognostic value.
View details for DOI 10.1016/j.stem.2017.01.007
View details for PubMedID 28157493
RAS/MAPK Activation Drives Resistance to Smo Inhibition, Metastasis, and Tumor Evolution in Shh Pathway-Dependent Tumors.
2015; 75 (17): 3623-3635
The Hedgehog pathway is a potent regulator of cellular growth and plays a central role in the development of many cancers including basal cell carcinoma (BCC). The majority of BCCs arise from mutations in the Patched receptor resulting in constitutive activation of the Hedgehog pathway. Secondary driver mutations promote BCC oncogenesis and occur frequently due to the high mutational burden resulting from sun exposure of the skin. Here, we uncover novel secondary mutations in Suppressor of Fused (SUFU), the major negative regulator of the Hedgehog pathway. SUFU normally binds to a Hedgehog transcriptional activator, GLI1, in order to prevent it from initiating transcription of Hedgehog target genes. We sequenced tumor-normal pairs from patients with early sporadic BCCs. This resulted in the discovery of nine mutations in SUFU, which were functionally investigated to determine whether they help drive BCC formation. Our results show that four of the SUFU mutations inappropriately activate the Hedgehog pathway, suggesting they may act as driver mutations for BCC development. Indeed, all four of the loss of function SUFU variants were found to disrupt its binding to GLI, leading to constitutive pathway activation. Our results from functional characterization of these mutations shed light on SUFU's role in Hedgehog signaling, tumor progression, and highlight a way in which BCCs can arise.
View details for DOI 10.1371/journal.pone.0168031
View details for Web of Science ID 000391222000030
View details for PubMedID 28030567
View details for PubMedCentralID PMC5193403
Smoothened variants explain the majority of drug resistance in Basal cell carcinoma.
2015; 27 (3): 342-353
Aberrant Shh signaling promotes tumor growth in diverse cancers. The importance of Shh signaling is particularly evident in medulloblastoma and basal cell carcinoma (BCC), where inhibitors targeting the Shh pathway component Smoothened (Smo) show great therapeutic promise. However, the emergence of drug resistance limits long-term efficacy, and the mechanisms of resistance remain poorly understood. Using new medulloblastoma models, we identify two distinct paradigms of resistance to Smo inhibition. Sufu mutations lead to maintenance of the Shh pathway in the presence of Smo inhibitors. Alternatively activation of the RAS-MAPK pathway circumvents Shh pathway dependency, drives tumor growth, and enhances metastatic behavior. Strikingly, in BCC patients treated with Smo inhibitor, squamous cell cancers with RAS/MAPK activation emerged from the antecedent BCC tumors. Together, these findings reveal a critical role of the RAS-MAPK pathway in drug resistance and tumor evolution of Shh pathway-dependent tumors. Cancer Res; 75(17); 3623-35. ©2015 AACR.
View details for DOI 10.1158/0008-5472.CAN-14-2999-T
View details for PubMedID 26130651
View details for PubMedCentralID PMC4558230
Epigenetic targeting of Hedgehog pathway transcriptional output through BET bromodomain inhibition
2014; 20 (7): 732-740
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
View details for PubMedCentralID PMC4357167
Advanced treatment for basal cell carcinomas.
Cold Spring Harbor perspectives in medicine
2014; 4 (7)
Epigenetic targeting of hedgehog pathway transcriptional output.
2014; 16 Suppl 3: iii25
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 Web of Science ID 000338689500015
Reduced expression of GDF-15 is associated with atrophic inflammatory lesions of the prostate.
(blind field)We used ligand and genetic activation of the Hedgehog pathway to study the effects of BET bromodomain inhibition on Hedgehog pathway transcriptional output. Furthermore, we studied the in vitro and in vivo efficacy of BET bromodomain inhibitors using tumor cells generated from genetically engineered mouse (GEM) and patient derived xenograft models of Hedgehog driven tumors, including a panel of tumors resistant to the current FDA-approved Smoothened antagonists.We show that knockdown of BRD4 or treatment with the BET bromodomain inhibitor, JQ1, dramatically inhibits transcription of GLI1, GLI2 and other Hedgehog target genes upon ligand-mediated or genetic activation of the Hedgehog pathway. We confirm the inhibitory effect of JQ1 occurs downstream of SMO and SUFU and verify by chromatin immunoprecipitation that BRD4 directly occupies the GLI1 and GLI2 promoters with a substantial decrease in the engagement of these genomic sites upon treatment with JQ1. We observe a corresponding downregulation of genes associated with medulloblastoma-specific GLI1 binding sites upon exposure to JQ1, confirming the direct regulation of GLI1 by BET bromodomain proteins. Finally, in patient- and GEM-derived cells of Hedgehog-driven cancer (basal cell carcinoma, medulloblastoma and atypical teratoid/rhabdoid tumor), we show that JQ1 decreases Hh pathway output and proliferation, even in cells resistant to Smoothened inhibitors.These results expand the role of BET bromodomain inhibitors to targeting Hedgehog-driven cancers and highlight a strategy that overcomes the limitation of Hedgehog pathway inhibitors currently in clinical use.Pediatrics.
View details for DOI 10.1093/neuonc/nou208.9
View details for PubMedID 25165259
Growth differentiation factor-15 (GDF-15) suppresses in vitro angiogenesis through a novel interaction with connective tissue growth factor (CCN2)
JOURNAL OF CELLULAR BIOCHEMISTRY
2013; 114 (6): 1424-1433
Accumulating evidence suggests that chronic prostatic inflammation may lead to prostate cancer development. Growth differentiation factor-15 (GDF-15) is highly expressed in the prostate and has been associated with inflammation and tumorigenesis.To examine the relationship between GDF-15 and prostatic inflammation, GDF-15 expression was measured by immunohistochemical (IHC) staining in human prostatectomy specimens containing inflammation. The relationship between GDF-15 and specific inflammatory cells was determined using non-biased computer image analysis. To provide insight into a potential suppressive role for GDF-15 in inflammation, activation of inflammatory mediator nuclear factor of kappa B (NFκB) was measured in PC3 cells.GDF-15 expression in luminal epithelial cells was decreased with increasing inflammation severity, suggesting an inverse association between GDF-15 and inflammation. Quantification of IHC staining by image analysis for GDF-15 and inflammatory cell markers revealed an inverse correlation between GDF-15 and CD3+, CD4+, CD8+, CD68+, and inos+ leukocytes. GDF-15 suppressed NFκB activity in luciferase reporter assays. Expression of the NFκB target, interleukin 8 (IL-8), was downregulated by GDF-15.The inverse relationship between GDF-15 and inflammation demonstrates a novel expression pattern for GDF-15 in the human prostate and suppression of NFκB activity may shed light on a potential mechanism for this inverse correlation. Prostate © 2014 Wiley Periodicals, Inc.
View details for DOI 10.1002/pros.22911
View details for PubMedID 25327758
"Patch"ing up our tumor signaling knowledge.
journal of investigative dermatology
2013; 133 (5): 1131-1133
Growth differentiation factor-15 (GDF-15) and the CCN family member, connective tissue growth factor (CCN2), are associated with cardiac disease, inflammation, and cancer. The precise role and signaling mechanism for these factors in normal and diseased tissues remains elusive. Here we demonstrate an interaction between GDF-15 and CCN2 using yeast two-hybrid assays and have mapped the domain of interaction to the von Willebrand factor type C domain of CCN2. Biochemical pull down assays using secreted GDF-15 and His-tagged CCN2 produced in PC-3 prostate cancer cells confirmed a direct interaction between these proteins. To investigate the functional consequences of this interaction, in vitro angiogenesis assays were performed. We demonstrate that GDF-15 blocks CCN2-mediated tube formation in human umbilical vein endothelial (HUVEC) cells. To examine the molecular mechanism whereby GDF-15 inhibits CCN2-mediated angiogenesis, activation of αV β3 integrins and focal adhesion kinase (FAK) was examined. CCN2-mediated FAK activation was inhibited by GDF-15 and was accompanied by a decrease in αV β3 integrin clustering in HUVEC cells. These results demonstrate, for the first time, a novel signaling pathway for GDF-15 through interaction with the matricellular signaling molecule CCN2. Furthermore, antagonism of CCN2 mediated angiogenesis by GDF-15 may provide insight into the functional role of GDF-15 in disease states.
View details for DOI 10.1002/jcb.24484
View details for Web of Science ID 000317864800022
View details for PubMedID 23280549
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