Dear Asha,

Disrupting the Notch signalling pathway has a great potential in treating a variety of severe health conditions.

The following is a recent publication on this topic:

Consequences of Disrupted Notch Signaling in Bladder Cancer

By: Annemarie Greife, Michèle J. Hoffmann and Wolfgang A. Schulz

European Urology, Volume 68 Issue 1, July 2015, Pages 3-4

Published online: 01 July 2015

http://www.europeanurology.com/article/S0302-2838(15)00199-2/fulltext/consequences-of-disrupted-notch-signaling-in-bladder-cancer

Take Home Message

The Notch pathway, which controls stem cell maintenance and cell differentiation, is activated in certain cancers and therefore constitutes a therapeutic target. Especially in invasive urothelial carcinoma, the pathway is inactivated instead, and drugs inhibiting Notch signaling are likely contra-indicated.

TABLE OF CONTENTS

Abstract

Conflicts of interest

Funding support

References

Footnotes

Article information

The Notch signaling pathway is an attractive target for anticancer drugs [1] because it helps maintain stem and precursor cells in many tissues (eg, gut and glandular tissues) and, accordingly, in the cancer stem cells that originate from them [2] . In contrast, Notch signaling promotes differentiation in other tissues, notably, squamous epithelia of various organs and the skin. Consequently, the pathway is often disrupted in cancers arising from squamous epithelia by mutations inactivating crucial components like the receptors NOTCH1, NOTCH2, or NOTCH3. Accordingly, pharmacologic inhibition of Notch signaling is contraindicated in these cancers.

Until recently, very little was known about the function of the pathway in the urothelium or about its state in cancers of the bladder. Now, within a few months, three papers have appeared that, despite different emphases and some divergence in molecular details, agree on the most important issue, namely, that Notch signaling is frequently inactivated in bladder cancer[3], [4], and [5]. This means that drugs inhibiting the pathway overall are unlikely to be beneficial in the treatment of bladder cancer. Indeed, such inhibitors do not diminish proliferation of urothelial carcinoma (UC) cell lines [3] . Instead, they could exert adverse effects on healthy urothelium if applied for the treatment of cancers with Notch overactivity in other organs. A prominent example of such adverse effects is the development of squamous skin cancers in clinical trials of γ-secretase inhibitors for Alzheimer's disease [6] .

Another major conclusion of the three papers is that inactivation of Notch signaling occurs predominantly in bladder cancers with squamous features but rarely or less completely in UC with papillary or luminal features. Because the precise stratification of UC into molecular subtypes is still intensely debated (as discussed by McConkey et al [7] ), this conclusion is likely to be refined by further studies. Nevertheless, the experiments conducted by Maraver et al [5] using genetically engineered mice with a defective Notch pathway in the urothelium suggest a direct role for Notch inactivation in squamous dedifferentiation. Moreover, these authors provide experimental evidence that Notch signaling impedes epithelial–mesenchymal transition. Consequently, Notch pathway inactivation appears to be associated with a more aggressive phenotype of UC, in line with an older report [8] .

The three studies have identified several factors contributing to the inactivation of Notch signaling, especially mutations in NOTCH receptors and the nuclear coactivator protein MAML1 ( Fig. 1 ). For several NOTCH1 and NOTCH2 mutations, Rampias et al [4] and Maraver et al [5] demonstrated that the mutations indeed inactivate the function of the receptors. Furthermore, the receptors and several presumable target genes of the pathway are downregulated. Interestingly, theNOTCH1gene is located on the long arm of chromosome 9, so its downregulation may be a consequence of 9q loss and may help explain why this particular chromosomal alteration is so common in UC.

Fig. 1 The Notch pathway in bladder cancer. (A) Notch signaling involves interactions between a ligand like delta-like 1 (DLL1), Jagged 1 (JAG1), or Jagged 2 (JAG2) and a receptor like NOTCH1 or NOTCH2 on adjacent cells. Productive interactions allow cleavage of the engaged receptor by the γ-secretase complex to produce an active NOTCH1 intracellular domain (NICD) fragment that travels to the nucleus. In bladder cancers, NOTCH1, NOTCH2, and, more rarely, NOTCH3 or components of the γ-secretase complex are mutated. (B) In the nucleus, an NICD fragment associates with the transcription factor CSL and coactivators, especially MAML1, resulting in the transcription of factors like HES1, which represses or activates further genes. MAML1 is mutated in some cases of bladder cancer. In urothelial cells, HES1 is proposed to activate DUSP genes, which encode dual-specific phosphatases inactivating ERK1 or ERK2 protein kinases. Extracellular signal-related kinase (ERK) becomes phosphorylated and active by mitogen-activated protein kinase signaling in response to extracellular growth factors (FGF or EGF family) or in urothelial carcinoma by oncogenic mutations in FGF or EGF receptors or RAS proteins. (C) Postulated consequences of Notch signaling in the urothelium. Its inactivation is proposed to favor ERK-mediated proliferation, squamous dedifferentiation, and epithelial–mesenchymal transition. Other effects remain to be explored. EMT = epithelial–mesenchymal transition; ERK = extracellular signal-related kinase; MAPK = mitogen-activated protein kinase; N1 = NOTCH1; N2 = NOTCH2; NICD = NOTCH1 intracellular domain. Flash symbols in (A) and (B) show molecules mutated in UC.

Another important finding with clinical implications is a direct effect of Notch signaling on the mitogen-activated protein kinase (MAPK) signaling pathway [4] . In many UCs, especially papillary and luminal tumors, this pathway is overactive due to upstream FGFR3 or HRAS mutations. Ultimately, these result in enhanced phosphorylation and concomitant activity of extracellular signal-related kinase (ERK) protein kinases that mediate most of the MAPK pathway's effects on cell proliferation. The activity of the ERKs is terminated by dual-specificity phosphatase (DUSP) protein phosphatases. Rampias et al demonstrated that several of these enzymes are induced by active NOTCH1 in UC cell lines ( Fig. 1 ). Inactivation of Notch signaling results in diminished DUSP activity and prolonged ERK activation and is expected to diminish the dependence of ERK activity on upstream signals, which is a characteristic of many invasive UCs [9] . Moreover, the authors find an inverse relationship between FGFR3 and Notch pathway mutations in UC tissues and propose that Notch inactivation may underlie the activation of MAPK signaling in invasive UC, in which FGFR3 or HRAS mutations are infrequent. Notably, many modern targeted anticancer drugs inhibit signal tyrosine receptor kinases or signal-transducing proteins upstream of ERK, but so far have shown little clinical benefit in bladder cancer treatment. Diminished dependence of ERK activity on upstream signals due to disrupted Notch signaling might constitute a factor responsible for their low efficacy.

Many questions on the cellular and molecular causes and effects of Notch signaling inactivation in bladder cancer remain to be answered. These include how its effects on normal urothelial cell and tissue differentiation are mediated, which ligands of the NOTCH receptors are active in the normal urothelium and how they change in cancers, and whether NOTCH1 and NOTCH2 mutations have equivalent consequences. Specifically, Notch signaling deserves closer investigation in the various forms of squamous cell carcinoma of the bladder [10] . Importantly, further studies in larger cohorts are required to evaluate the impact of Notch pathway inactivation on patient prognosis and on response to targeted and conventional chemotherapy in bladder cancer. Finally, as pointed out by Rampias et al [4] , Notch pathway agonists should be considered for pharmacologic bladder cancer therapy, whereas antagonists are obviously unsuitable. The expected tumor-promoting effects of agonists on other organs might be avoided by intravesical application.

Conflicts of interest

The authors have nothing to disclose.

Funding support

The authors’ work on Notch in bladder cancer was supported by the Krebsgesellschaft NRW and the Jürgen-Manchot-Foundation, which were not involved in the design and conduct of the study.

References

[1] I. Espinoza, L. Miele. Notch inhibitors for cancer treatment. Pharmacol Ther. 2013;139:95-110 Crossref

[2] A.M. Egloff, J.R. Grandis. Molecular pathways: context-dependent approaches to Notch targeting as cancer therapy. Clin Cancer Res. 2012;18:5188-5195 Crossref

[3] A. Greife, S. Jankowiak, J. Steinbring, et al. Canonical Notch signalling is inactive in urothelial carcinoma. BMC Cancer. 2014;14:628

[4] T. Rampias, P. Vgenopoulou, M. Avgeris, et al. A new tumor suppressor role for the Notch pathway in bladder cancer. Nat Med. 2014;20:1199-1205

[5] A. Maraver, P.J. Fernandez-Marcos, T.P. Cash, et al. NOTCH pathway inactivation promotes bladder cancer progression. J Clin Invest. 2015;125:824-830

[6] C. Groth, M.E. Fortini. Therapeutic approaches to modulating Notch signaling: current challenges and future prospects.Semin Cell Dev Biol. 2012;23:465-472 Crossref

[7] D.J. McConkey, W. Choi, C.P. Dinney. New insights into subtypes of invasive bladder cancer: considerations of the clinician. Eur Urol. 2014;66:609-610

[8] T.P. Shi, H. Xu, J.F. Wei, et al. Association of low expression of notch-1 and jagged-1 in human papillary bladder cancer and shorter survival. J Urol. 2008;180:361-366 Crossref

[9] W.A. Schulz. Understanding urothelial carcinoma through cancer pathways. Int J Cancer. 2006;119:1513-1518 Crossref

[10] N.T. Gaisa, T. Braunschweig, N. Reimer, et al. Different immunohistochemical and ultrastructural phenotypes of squamous differentiation in bladder cancer. Virchows Arch. 2011;458:301-312 Crossref

Hoping this will be helpful,

Rafik

disrupting notch will trigger varied differentiation pathways

The Notch pathway is extremely complicated, so unfortunately, the answer is not simple. First of all, the distribution of the different Notch receptors (1-4) in the system will have a role when targeting angiogenesis. Secondly, the Notch ligand present. Dll4 in the endothelial tip cells will promote sprouting angiogenesis, but Dll4 over-expression in the general endothelial population will cause quite a different effect, partly due to the disruptions in the tip and stalk phenotype. Furthermore, Jagged1, another Notch ligand, has quite a different role in angiogenesis compared with Dll4. So, one must investigate the relative importance between the different Notch ligands in a given system to appreciate if Notch inhibition can be an effective anti-angiogenic strategy. 

Hi Asha,

I totally agree with Xi Ye, targeting Notch signaling can have very different end results depending on the specific coupling ligand/receptor that the drug is able to target. For instance targeting Jag1 has  a very strong anti-angiogenic effect, with the vessels being less dense, perfused and matured, so much more leakier (see: http://www.ncbi.nlm.nih.gov/pubmed/26213336), unlike inhibiting Dll4 which will have the opposite effect (increased density), even though the end result in tumor growth will be the same. So, in the end it really depends on the desired effect on angiogenesis that you want to achieve with the therapy. And also, if the anti-angiogenic therapy is to be combined with other drugs, because when altering the vasculature status of the tumour you can also be interfering with the delivery of your adjuvant drug.

Moreover, you also have to consider the effect of blocking Notch directly on tumor cells, and in this regard Jagged1 has been very well described in its roles regarding tumor cell proliferation, EMT, metastatization, etc... (see: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4174884/).

Hope this helps,

Best,

Rita

Article Endothelial Jagged1 promotes solid tumor growth through both...

thanks everyone ^^