Skip Navigation LinksHome > January 2007 - Volume 2 - Issue 1 > Hedgehog Signaling Pathway and Lung Cancer
Journal of Thoracic Oncology:
doi: 10.1097/JTO.0b013e31802c0276
Pathway of the Month

Hedgehog Signaling Pathway and Lung Cancer

Velcheti, Vamsidhar MD*; Govindan, Ramaswamy MD*†

Free Access
Article Outline
Collapse Box

Author Information

*Division of Oncology, Department of Medicine and †Alvin J. Siteman Cancer Center, Washington University School of Medicine, St. Louis, MO.

Address for correspondence: Dr. Ramaswamy Govindan, Division of Medical Oncology, Washington University School of Medicine, 4960 Children’s Place, Box 8056, St. Louis, MO 63110. E-mail:

Collapse Box


Signaling pathways responsible for embryogenesis play a critical role in the maintenance of stem cells in adult life and cellular responses to injury. Dysfunction of the developmental signaling pathways during adult homeostasis leads to various events resulting in the development of neoplasia. We review the biology of the hedgehog signaling pathway and its potential role in the development of lung cancer.

Signaling pathways responsible for embryogenesis appear to play a critical role in the maintenance of stem cells in adult life and cellular responses to injury. Dysregulation of these signaling pathways during adult homeostasis can lead to various events resulting in the development of neoplasia (Figure 1).

Figure 1
Figure 1
Image Tools

Hedgehog (Hh) signaling pathway is one such pathway that is crucial in the embryogenesis. Hh pathway also plays a central role in the repair and regeneration of adult tissue. The Hh signaling pathway was first studied in drosophilae. During embryonic development, drosophilae with a mutation in the Hh gene were covered with pointed denticles, resembling a hedgehog, hence the name. Several studies have recently demonstrated that dysregulation of the Hh signaling plays a role in several cancers including the brain, skin, gastrointestinal tract, pancreas, and lung.1–6

Back to Top | Article Outline


Mammalian Hh signaling pathway (Figure 2) constitutes (a) Hh ligand with three variants: desert (Dhh), Indian (Ihh), and sonic (Shh); (b) a transmembrane receptor-patched homolog 1 and 2 (Ptch1 and 2); (c) smoothened (Smo), a G protein–coupled receptor; and (d) a cytoplasmic complex that regulates the cubitus interruptus (Ci) or glioma-associated oncogene homolog (Gli) family of transcriptional effectors. All the three ligands bind to the same receptors and elicit similar responses. Shh is the most extensively characterized variant and is widely expressed during embryogenesis. Shh acts as a morphogen and plays an important role in the formation of the neural tube, axial skeleton, primitive gut, and the tracheobronchial tree.7,8

Figure 2
Figure 2
Image Tools

Autocatalytic cleavage and coupling of cholesterol are the essential posttranslational processes that maintain the signaling capability of the Hh ligands.9 The secretion of the functional Hh ligand by the Hh-secreting cell is dependent on the availability of dispatched (Disp), a transmembrane protein with homology to patched (Ptch), which is an Hh receptor on the Hh responsive cell.10,11

The Ptch 1 and 2 are membrane receptors for Hh ligands. Ptch 1 is more widely expressed and well characterized. Binding of Hh ligand with the Ptch alters the interactions of Ptch with Smo, resulting in the activation of Smo. This initiates a cascade of events resulting in the Ci and Gli entering the nucleus and acting as transcriptional activators. It is unclear how the activation of Smo communicates with the cytoplasmic Ci/Gli transcription factor complex. Gli bind to the DNA through zinc finger domains directed to particular target genes regulating key cell survival and differentiation functions. Gli1 is a transcription activator, and Gli2 and Gli3 are both activators and repressors of transcription. Gli3 and Ci regulate transcription by binding to the CREB-binding protein, which is a transcription coactivator. Cyclin D and cyclin E are known transcriptional targets of Hh signaling, and these proteins are vital in the G1-to-S transition in the cell cycle.12 Hh signaling activates the mitosis promoting factor by increasing the intranuclear availability of cyclin B.13 Hh signaling also opposes normal stimuli for epithelial cell cycle arrest (by inhibiting P21) and promotes cell growth.14 Hh signaling inhibits a well-known regulator of apoptosis, the p53 tumor suppressor gene.15

When the Hh ligand is unavailable Ptch1 inhibits the activity of Smo, thus repressing the downstream signaling events. When the Hh signaling is lacking, Gli proteins are bound to microtubules in the cytosol along with a multiprotein complex consisting of Fused (Fu) and suppressor of Fu (SuFu).

The Hh operates through a series of inhibitory steps. The availability of the Hh ligand for signaling is regulated by the expression of Hh interacting protein (HIP) on the cell surface of Hh responsive cell. The HIP is a membrane glycoprotein that binds to Hh ligands with an affinity similar to that of the membrane protein Ptch1. HIP lacks signal transduction capacity and acts to internalize and degrade the Hh ligand.16 Activation of the Hh pathway causes an increased expression of the HIP via a negative feedback mechanism, thus serving as an inducible antagonist of Shh signaling.16 The Hh signaling is regulated at various levels, indicating the importance of tight control of Hh signaling. Several inhibitors of the pathway like Ptch and HIP are transcriptional target genes and Hh activation induces negative feedback, reducing the intensity of Hh signaling. Gli genes are regulated by complex mechanisms at both the posttranslational and transcriptional level. Hh signaling up-regulates Gli1 expression while repressing Gli3 expression.5

Dysregulation of the Hh signaling can occur from ligand-dependent and -independent mechanisms (Table 1).

Table 1
Table 1
Image Tools
Back to Top | Article Outline


The lungs develop from an outpouching of the primitive endodermal tube into the surrounding mesenchyme. In the developing lung in mouse models, an elevated Shh expression was detected in the tracheal diverticulum and in the trachea and lung endoderm.17 Studies indicate that the Hh signaling pathway is essential for the growth and differentiation of the trachea and lung, and aberrations in the signaling components may be involved in abnormal development of the lung.7,8,17 Natural teratogens like cyclopamine and jervine (extracted from of corn lilies) are inhibitors of Hh signaling. Pregnant animals treated with these inhibitors of Hh signaling at an early gestation period results in multiple developmental anomalies including abnormal lung development.18

The airway epithelial progenitor (stem) cells play an important role in the development of the respiratory epithelium. The differentiation of these progenitor cells to form the neuroendocrine or non-neuroendocrine (ciliated, mucous, clara, or basal cells) component of the respiratory epithelium is tightly regulated by a complex bipotential notch signaling.6,19 Notch and Wnt signaling are evolutionary conserved signaling pathways tightly regulating cell death, cell movement, and cell division and differentiation during embryogenesis. During development and repair of the lung epithelium, Hh signaling maintains this bipotential notch signaling.6,19 Hh and Wnt pathways possibly play an important role in the maintenance and the expansion of the progenitor (stem) cells during development and can mediate lung growth by signaling to adjacent lung mesenchyme.20

Back to Top | Article Outline


Hh signaling is possibly inactive in the human adult lung epithelium except in the epithelial progenitor (stem) cells. This persistence of Hh signaling in the epithelial progenitor (stem) cells could help maintain these cells and play a critical role in the response to airway epithelial injury.6,19,21 Studies on animal lung airway epithelial injury/regeneration model suggest that persistent injury to the airway is a potent stimulus for the activation of the Hh signaling, and this helps the expansion of airway epithelial progenitor cells.6,19,21 Shh and Gli1 are expressed in the regenerating lung airway epithelium.6 Studies on cell lines showed that all the seven small cell lung cancer (SCLC) and seven non-small cell lung cancer (NSCLC) cell lines expressed Shh protein. Five of seven SCLC cell lines expressed both Shh and Gli1 in contrast to NSCLC, which expressed only Shh but not Gli1.6 Analysis of clinical samples of human lung cancer tissue demonstrated 50% (five of 10) of SCLC expressed both Shh and Gli1 compared to only 10% (four of 40) of NSCLC.6 Another study investigating the expression of Gli1 in SCLC tissue reported that 85% (34 of 40) of SCLC express Gli1 and more than 60% have a medium to strong expression correlating with increased Hh signaling.22 It thus appears that lung cancer cells retain aspects of the Hh signaling seen in the primitive lung endodermal cells. However, the degree of dependence on this signaling varies ahmong the subtypes of lung cancer. Inhibition of Shh ligand activity using monoclonal antibody and cyclopamine resulted in the significant growth inhibition in SCLC cell lines expressing both Shh and Gli but not NSCLC cell lines (which do not express both Shh and Gli).6 Similar results were found in in vivo studies on lung cancer xenografts in nude mice.6

HIP is a natural antagonist of Hh signaling as discussed above. Reduced expression of HIP as been reported in lung cancer A549 cell line xenograft in nude mice and a decrease in the expression of HIP was seen in five of 10 human NSCLC tissues.23 Experimental models studying HIP knockout mice confirmed increased Hh signaling.24,25 There appears to be down-regulation of HIP in endothelial cells during angiogenesis.23 These findings suggest that reduced expression of HIP could potentially enhance the Hh signaling and possibly facilitate angiogenesis. Hh signaling thus appears to play a role in proliferation of malignant cells and promote angiogenesis.

Back to Top | Article Outline


Therapeutic inactivation of the Hh signaling offers a potential treatment for cancer. Inactivation of the Hh signaling can be done at various levels, mainly (1) extracellular blocking of the Shh ligands using Shh antibodies, (2) activation of Smo in the cell membrane, (3) modulating intracytoplasmic regulators of Hh signaling like protein kinase A and SuFu, and (4) altering the intranuclear functioning of Gli.

Curis Inc. developed a Shh antagonist that showed promising results in preclinical models.26,27 Antibodies to Shh are currently being evaluated in phase I clinical trials for basal cell carcinoma. Cyclopamine is another potential molecule of interest for the inhibition of Hh signaling.26,27 Cyclopamine has demonstrated a good safety profile in mice.2,4,6 Several other compounds that bind to Smo and inhibit the downstream events have been identified (KAAD-cyclop, SANT1-4, CUR61414).28 However, patients with downstream alterations in the Hh signaling could be resistant to the treatment with Shh antagonist and Smo targeted therapies. Another potential mechanism for blocking Gli activity is the use of protein kinase A agonists like forskolin, which maintain the Gli in inactive state.29 Antisense oligonucleotides targeting Gli RNA also provide a viable option to prevent Gli-mediated activation of target genes.3,30

It is important to clarify the role of activation of Hh pathway in the process of carcinogenesis and progression in lung cancer. Numerous mechanisms have been implicated in the development, proliferation, and progression of lung cancer; it is critical to understand how the Hh pathway interacts with the other pathways implicated in lung cancer. There have been virtually no significant advances in the systemic therapy of SCLC in the past three decades. With the current trend toward developing targeted therapies, the Hh pathway modulators offer a potential new avenue in the treatment of lung cancer.

Back to Top | Article Outline


1. Goodrich LV, Milenkovic L, Higgins KM, Scott MP. Altered neural cell fates and medulloblastoma in mouse patched mutants. Science 1997;277:1109–1113.

2. Berman DM, Karhadkar SS, Hallahan AR, et al. Medulloblastoma growth inhibition by hedgehog pathway blockade. Science 2002;297:1559–1561.

3. Sanchez P, Hernandez AM, Stecca B, et al. Inhibition of prostate cancer proliferation by interference with SONIC HEDGEHOG-GLI1 signaling. Proc Natl Acad Sci U S A 2004;101:12561–12566.

4. Thayer SP, di Magliano MP, Heiser PW, et al. Hedgehog is an early and late mediator of pancreatic cancer tumorigenesis. Nature 2003;425:851–856.

5. Bak M, Hansen C, Tommerup N, Larsen LA. The Hedgehog signaling pathway—implications for drug targets in cancer and neurodegenerative disorders. Pharmacogenomics 2003;4:411–429.

6. Watkins DN, Berman DM, Burkholder SG, Wang B, Beachy PA, Baylin SB. Hedgehog signalling within airway epithelial progenitors and in small-cell lung cancer. Nature 2003;422:313–317.

7. Mahlapuu M, Enerback S, Carlsson P. Haploinsufficiency of the forkhead gene Foxf1, a target for sonic hedgehog signaling, causes lung and foregut malformations. Development 2001;128:2397–2406.

8. Bellusci S, Furuta Y, Rush MG, Henderson R, Winnier G, Hogan BL. Involvement of sonic hedgehog (Shh) in mouse embryonic lung growth and morphogenesis. Development 1997;124:53–63.

9. Gallet A, Rodriguez R, Ruel L, Therond PP. Cholesterol modification of hedgehog is required for trafficking and movement, revealing an asymmetric cellular response to hedgehog. Dev Cell 2003;4:191–204.

10. Burke R, Nellen D, Bellotto M, et al. Dispatched, a novel sterol-sensing domain protein dedicated to the release of cholesterol-modified hedgehog from signaling cells. Cell 1999;99:803–815.

11. Tian H, Jeong J, Harfe BD, Tabin CJ, McMahon AP. Mouse Disp1 is required in sonic hedgehog-expressing cells for paracrine activity of the cholesterol-modified ligand. Development 2005;132:133–142.

12. Pasca di Magliano M, Hebrok M. Hedgehog signalling in cancer formation and maintenance. Nat Rev Cancer 2003;3:903–911.

13. Barnes EA, Kong M, Ollendorff V, Donoghue DJ. Patched1 interacts with cyclin B1 to regulate cell cycle progression. EMBO J 2001;20:2214–2223.

14. Fan H, Khavari PA. Sonic hedgehog opposes epithelial cell cycle arrest. J Cell Biol 1999;147:71–76.

15. Yoshinori A, Oda-Sato E, Tobiume K, et al. 2006. The negative regulation of p53 by hedgehog signaling. Presented at the AACR Annual Meeting, Washington, DC, 2006. (Abstract# 1135-b).

16. Chuang PT, McMahon AP. Vertebrate hedgehog signalling modulated by induction of a hedgehog-binding protein. Nature 1999;397:617–621.

17. Litingtung Y, Lei L, Westphal H, Chiang C. Sonic hedgehog is essential to foregut development. Nat Genet 1998;20:58–61.

18. Cooper MK, Porter JA, Young KE, Beachy PA. Teratogen-mediated inhibition of target tissue response to Shh signaling. Science 1998;280:1603–1607.

19. Watkins DN, Berman DM, Baylin SB. Hedgehog signaling: progenitor phenotype in small-cell lung cancer. Cell Cycle 2003;2:196–198.

20. Taipale J, Beachy PA. The hedgehog and Wnt signalling pathways in cancer. Nature 2001;411:349–354.

21. Watkins DN, Peacock CD. Hedgehog signalling in foregut malignancy. Biochem Pharmacol 2004;68:1055–1060.

22. Vestergaard J, Pedersen MW, Pedersen N, et al. Hedgehog signaling in small-cell lung cancer: frequent in vivo but a rare event in vitro. Lung Cancer 2006;52:281–290.

23. Olsen CL, Hsu PP, Glienke J, Rubanyi GM, Brooks AR. Hedgehog-interacting protein is highly expressed in endothelial cells but down-regulated during angiogenesis and in several human tumors. BMC Cancer 2004;4:43.

24. Kawahira H, Ma NH, Tzanakakis ES, McMahon AP, Chuang PT, Hebrok M. Combined activities of hedgehog signaling inhibitors regulate pancreas development. Development 2003;130:4871–4879.

25. Chuang PT, Kawcak T, McMahon AP. Feedback control of mammalian hedgehog signaling by the hedgehog-binding protein, Hip1, modulates Fgf signaling during branching morphogenesis of the lung. Genes Dev 2003;17:342–347.

26. Hua Tian DM, Ahn C, Modrusan Z, et al. 2006. Characterization of a Hedgehog pathway antagonist in a mouse medulloblastoma allograft model (abstract 5639). Presented at the 97th AACR Annual Meeting, Washington, DC, 2006.

27. Tang TT, Dongwei L, Reich M, et al. Inhibition of the Hedgehog pathway as a therapeutic approach for the treatment of basal cell carcinomas (abstract 3809). Presented at the 97th AACR Annual Meeting, Washington, DC, 2006.

28. Chen JK, Taipale J, Young KE, Maiti T, Beachy PA. Small molecule modulation of smoothened activity. Proc Natl Acad Sci U S A 2002;99:14071–14076.

29. Shindo N, Sakai A, Arai D, Matsuoka O, Yamasaki Y, Higashinakagawa T. The ESC-E(Z) complex participates in the hedgehog signaling pathway. Biochem Biophys Res Commun 2005;327:1179–1187.

30. Chang DZ. Synthetic miRNAs targeting the GLI-1 transcription factor inhibit division and induce apoptosis in pancreatic tumor cells (abstract 2718). Presented at the 97th AACR Annual Meeting, 2006, Washington, DC.

31. Oro AE, Higgins KM, Hu Z, Bonifas JM, Epstein EH Jr, Scott MP. Basal cell carcinomas in mice overexpressing sonic hedgehog. Science 1997;276:817–821.

32. Berman DM, Karhadkar SS, Maitra A, et al. Widespread requirement for hedgehog ligand stimulation in growth of digestive tract tumours. Nature 2003;425:846–851.

33. Ma X, Sheng T, Zhang Y, et al. Hedgehog signaling is activated in subsets of esophageal cancers. Int J Cancer 2006;118:139–148.

34. Ma X, Chen K, Huang S, et al. Frequent activation of the hedgehog pathway in advanced gastric adenocarcinomas. Carcinogenesis 2005;26:1698–1705.

35. Levanat S, Musani V, Komar A, Oreskovic S. Role of the hedgehog/patched signaling pathway in oncogenesis: a new polymorphism in the PTCH gene in ovarian fibroma. Ann N Y Acad Sci 2004;1030:134–143.

36. Sheng T, Li C, Zhang X. Activation of the hedgehog pathway in advanced prostate cancer. Mol Cancer 2004;3:29.

37. Martin ST, Sato N, Dhara S, et al. Aberrant methylation of the human hedgehog interacting protein (HHIP) gene in pancreatic neoplasms. Cancer Biol Ther 2005;4:728–733.

38. Hahn H, Wicking C, Zaphiropoulous PG, et al. Mutations of the human homolog of Drosophila patched in the nevoid basal cell carcinoma syndrome. Cell 1996;85:841–851.

39. Tostar U, Malm CJ, Meis-Kindblom JM, Kindblom LG, Toftgard R, Unden AB. Deregulation of the hedgehog signalling pathway: a possible role for the PTCH and SUFU genes in human rhabdomyoma and rhabdomyosarcoma development. J Pathol 2006;208:17–25.

40. Xie J, Murone M, Luoh SM, et al. Activating smoothened mutations in sporadic basal-cell carcinoma. Nature 1998;391:90–92.

41. Grachtchouk M, Mo R, Yu S, et al. Basal cell carcinomas in mice overexpressing Gli2 in skin. Nat Genet 2000;24:216–217.

42. Taylor MD, Liu L, Raffel C, et al. Mutations in SUFU predispose to medulloblastoma. Nat Genet 2002;31:306–310.

Cited By:

This article has been cited 11 time(s).

Lung Cancer
The combination of Young's syndrome and small cell lung cancer-A spiky connection?
Forster, M; Enting, D; Nicholson, AG; O'Brien, M; Popat, S
Lung Cancer, 67(3): 372-375.
Journal of Biological Chemistry
HDAC4 Represses Vascular Endothelial Growth Factor Expression in Chondrosarcoma by Modulating RUNX2 Activity
Sun, XJ; Wei, L; Chen, Q; Terek, RM
Journal of Biological Chemistry, 284(): 21881-21890.
Journal of Thoracic Oncology
Novel systemic therapies for small cell lung cancer
Rudin, CM; Hann, CL; Peacock, CD; Watkins, DN
Journal of Thoracic Oncology, 4(9): S103-S106.

International Journal of Oncology
Role of Hedgehog signaling pathway in proliferation and invasiveness of hepatocellular carcinoma cells
Cheng, WT; Xu, K; Tian, DY; Zhang, ZG; Liu, LJ; Chen, Y
International Journal of Oncology, 34(3): 829-836.
Journal of Thoracic Disease
Hedgehog signaling pathway: the must, the maybe and the unknown
Zarogoulidis, P; Zarampouka, K; Huang, HD; Darwiche, K; Huang, Y; Sakkas, A; Zarogoulidis, K
Journal of Thoracic Disease, 5(2): 195-197.
Expression of Bmi1, FoxF1, Nanog, and gamma-Catenin in Relation to Hedgehog Signaling Pathway in Human Non-small-Cell Lung Cancer
Gialmanidis, IP; Bravou, V; Petrou, I; Kourea, H; Mathioudakis, A; Lilis, I; Papadaki, H
Lung, 191(5): 511-521.
World Journal of Surgical Oncology
Expression of glioma-associated oncogene 2 (Gli 2) is correlated with poor prognosis in patients with hepatocellular carcinoma undergoing hepatectomy
Zhang, DW; Cao, LQ; Li, Y; Lu, HW; Yang, XW; Xue, P
World Journal of Surgical Oncology, 11(): -.
Current Cancer Drug Targets
Inhibition of Hedgehog/Gli Signaling by Botanicals: A Review of Compounds with Potential Hedgehog Pathway Inhibitory Activities
Drenkhahn, SK; Jackson, GA; Slusarz, A; Starkey, NJE; Lubahn, DB
Current Cancer Drug Targets, 13(5): 580-595.

Chinese Journal of Cancer Research
Activation of sonic hedgehog signaling pathway is an independent potential prognosis predictor in human hepatocellular carcinoma patients
Che, L; Yuan, YH; Jia, J; Ren, J
Chinese Journal of Cancer Research, 24(4): 323-331.
Journal of Thoracic Oncology
A Phase II Study of Carboplatin, Etoposide, and Exisulind in Patients with Extensive Small Cell Lung Cancer: CALGB 30104
for the Cancer and Leukemia Group B, ; Govindan, R; Wang, X; Baggstrom, MQ; Burdette-Radoux, S; Hodgson, L; Vokes, EE; Green, MR
Journal of Thoracic Oncology, 4(2): 220-226.
PDF (385) | CrossRef
The American Journal of the Medical Sciences
Small Cell Lung Cancer: Are We Making Progress?
Dowell, JE
The American Journal of the Medical Sciences, 339(1): 68-76.
PDF (375) | CrossRef
Back to Top | Article Outline

Hedgehog signaling; Lung cancer

© 2007International Association for the Study of Lung Cancer


Article Tools



Search for Similar Articles
You may search for similar articles that contain these same keywords or you may modify the keyword list to augment your search.

Other Ways to Connect



Visit on your smartphone. Scan this code (QR reader app required) with your phone and be taken directly to the site.

 For additional oncology content, visit LWW Oncology Journals on Facebook.