Molecular Mechanisms of Epithelial to Mesenchymal Transition Regulated by ERK5 Signaling
Authors: Lucio Miele
Margarite D Matossian
Akshita B Bhatt
Patrick T Flaherty
Jane E Cavanaugh
Deniz A Ucar
Saloni Patel
Matthew E Burow
Journal: Biomolecules (2021)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: EMT; ERK5; cancer metastases; therapy.
Affiliations: Department of Pharmacology, School of Pharmacy, Duquesne University, Pittsburgh, PA 15282, USA., Department of Medicinal Chemistry, School of Pharmacy, Duquesne University, Pittsburgh, PA 15282, USA., Department of Medicine, Tulane University School of Medicine, New Orleans, LA 70112, USA., Department of Genetics and Stanley S. Scott Cancer Center, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA.

Abstract:  Extracellular signal-regulated kinase (ERK5) is an essential regulator of cancer progression, tumor relapse, and poor patient survival. Epithelial to mesenchymal transition (EMT) is a complex oncogenic process, which drives cell invasion, stemness, and metastases. Activators of ERK5, including mitogen-activated protein kinase 5 (MEK5), tumor necrosis factor α (TNF-α), and transforming growth factor-β (TGF-β), are known to induce EMT and metastases in breast, lung, colorectal, and other cancers. Several downstream targets of the ERK5 pathway, such as myocyte-specific enhancer factor 2c (MEF2C), activator protein-1 (AP-1), focal adhesion kinase (FAK), and c-Myc, play a critical role in the regulation of EMT transcription factors SNAIL, SLUG, and β-catenin. Moreover, ERK5 activation increases the release of extracellular matrix metalloproteinases (MMPs), facilitating breakdown of the extracellular matrix (ECM) and local tumor invasion. Targeting the ERK5 signaling pathway using small molecule inhibitors, microRNAs, and knockdown approaches decreases EMT, cell invasion, and metastases via several mechanisms. The focus of the current review is to highlight the mechanisms which are known to mediate cancer EMT via ERK5 signaling. Several therapeutic approaches that can be undertaken to target the ERK5 pathway and inhibit or reverse EMT and metastases are discussed. 

Retracted: No

PubPeer comments:
 Please beware -- this review includes many observations using the ERK5 inhibitor XMD8-92. However, as is now well known, this inhibitor is also an inhibitor of bromodomain proteins, and the bromodomain inhibition explains the vast majority of reported XMD8-92 effects. As a result, any observation cited in this paper that references use of this compound should be treated with EXTREME CAUTION. Please see these two references for further discussion. For some reason, the review does not cite them... ERK5 kinase activity is dispensable for cellular immune response and proliferation Emme C. K. Lin, Christopher M. Amantea, Tyzoon K. Nomanbhoy, Helge Weissig, Junichi Ishiyama, Yi Hu, Shyama Sidique, Bei Li, John W. Kozarich, and Jonathan S. Rosenblum PNAS October 18, 2016 113 (42) 11865-11870; first published September 27, 2016; https: doi.org 10.1073 pnas.1609019113 Discovery and Characterization of the Potent and Highly Selective (Piperidin-4-yl)pyrido[3,2-d]pyrimidine Based in Vitro Probe BAY-885 for the Kinase ERK5 Duy Nguyen*, Clara Lemos, Lars Wortmann*, Knut Eis, Simon J. Holton, Ulf Boemer, Dieter Moosmayer, Uwe Eberspaecher, Joerg Weiske, Christian Lechner, Stefan Prechtl, Detlev Suelzle, Franziska Siegel, Florian Prinz, Ralf Lesche, Barbara Nicke, Katrin Nowak-Reppel, Herbert Himmel, Dominik Mumberg, Franz von Nussbaum, Carl F. Nising, Marcus Bauser, and Andrea Haegebarth J. Med. Chem. 2019, 62, 2, 928u2013940 https: doi.org 10.1021 acs.jmedchem.8b01606 , 
 #1 Thank you so much for taking the time to comment. The effects of XMD8-92 as a dual ERK5 BRD4 inhibitor have been characterized on cell viability and proliferation. We have shown previously that XMD8-92-like effects on cell viability and proliferation can be recapitulated by AX15836 (ERK5 inhibitor) + CPI-203 (BRD4 inhibitor) combination: Wright TD, Raybuck C, Bhatt A, Monlish D, Chakrabarty S, Wendekier K, Gartland N, Gupta M, Burow ME, Flaherty PT, Cavanaugh JE. Pharmacological inhibition of the MEK5 ERK5 and PI3K Akt signaling pathways synergistically reduces viability in triple-negative breast cancer. J Cell Biochem. 2020 Feb;121(2):1156-1168. doi: 10.1002 jcb.29350. Epub 2019 Aug 28. PMID: 31464004; PMCID: PMC6923606. None of the new ERK5 inhibitors have been studied to understand EMT in cancer yet and therefore any comment on the new ERK5 inhibitors is beyond of the scope of the current review. Per the study below: Andrieu GP, Denis GV. BET Proteins Exhibit Transcriptional and Functional Opposition in the Epithelial-to-Mesenchymal Transition. Mol Cancer Res. 2018 Apr;16(4):580-586. doi: 10.1158 1541-7786.MCR-17-0568. Epub 2018 Feb 7. PMID: 29437854; PMCID: PMC5882530. BRD4 may not have a role in EMT at all and effects of XMD8-92 on EMT could be an on-target (ERK5-mediated) effect. This is however a speculation and further research is needed in the ERK5 EMT field with ERK5-selective inhibitors. We have studied the effects of ERK5 activation inhibition on EMT MET using constitutively active and dominant negative lentivirus vectors (since the inhibitors could be non-selective); however, we cannot comment much on the results yet because the pub is in review. Please be on the lookout for the paper. Looking forward to more discussion! , 
 #2 Dr. Bhatt, you have clearly stated why it s so reckless to cite the XMD8-92 effects on EMT MET: those effects haven t been confirmed using selective ERK5 inhibitors. If you knew those experiments haven t been done, and you knew selective inhibitors have been reported -- you ve even used one in your research -- why didn t you include such comments in the review? The review doesn t even cite the papers that report the selective inhibitors. Many papers have been published suggesting that ERK5 kinase inhibitors could be useful therapeutics for cancer because of activity of XMD8-92 or effects of recombinant expression of ERK5 mutants. But selective ERK5 inhibitors (AX15836, BAY-885) have never been shown to have activity that could translate to a useful oncology therapeutic. Publishing reviews that continue to suggest a future for ERK5 inhibitors in oncology therapy is a disservice to the scientific community as well as patients. , 
 Thank you for your comment. As stated above, we have shown that effect of XMD8-92 on cell proliferation, cell viability, and EMT (in press), can only be recapitulated with the use of a combination of AX15836 (ERK5 inhibitor) + CPI-203 (BRD4 inhibitor). Therefore, ERK5 inhibition does play a role in these processes. Accordingly, our publications are in preparation examining more specific ERK5 inhibitors, ERK5 knockout cells, siRNA for ERK5, and mutants (DN and CA) of MEK5 and ERK5 that suggest a role for ERK5 in cancer cell viability, proliferation, migration, and EMT . These data include both in vitro and in vivo data. We recognize your concern elucidating the role of MEK5 in cancer. Below are our review papers and papers from two external groups describing ERK5 overexpression and its correlation with poor patient survival. Bhatt, A.B.; Patel, S.; Matossian, M.D.; Ucar, D.A.; Miele, L.; Burow, M.E.; Flaherty, P.T.; Cavanaugh, J.E. Molecular Mechanisms of Epithelial to Mesenchymal Transition Regulated by ERK5 Signaling. Biomolecules 2021, 11, 183. https: doi.org 10.3390 biom11020183 Hoang VT, Yan TJ, Cavanaugh JE, Flaherty PT, Beckman BS, Burow ME. Oncogenic signaling of MEK5-ERK5. Cancer Lett. 2017 Apr 28;392:51-59. doi: 10.1016 j.canlet.2017.01.034. Epub 2017 Jan 30. PMID: 28153789; PMCID: PMC5901897. Miranda M, Rozali E, Khanna KK, Al-Ejeh F. MEK5-ERK5 pathway associates with poor survival of breast cancer patients after systemic treatments. Oncoscience. 2015;2(2):99-101. Published 2015 Feb 20. doi:10.18632 oncoscience.135 Simu00f5es AE, Rodrigues CM, Borralho PM. The MEK5 ERK5 signalling pathway in cancer: a promising novel therapeutic target. Drug Discov Today. 2016 Oct;21(10):1654-1663. doi: 10.1016 j.drudis.2016.06.010. Epub 2016 Jun 16. PMID: 27320690. Along with you, we look forward to realizing effective ERK5 pathway attenuation as a basis for effective anticancer therapy. , 
 So the suggestion is that ERK5 inhibition on its own doesn t have an effect on cell proliferation, viability, or EMT but ERK5 inhibition plus broad bromodomain inhibition does have such effects? And this very provocative suggestion is in press? So why not describe the synergistic inhibition that way and why include these unpublished results in a review? A review whose very title suggests that ERK5 regulates EMT?? A suggestion: if you have a cell model of EMT and you can t prevent transition by either AX15836 or BAY-885 at concentrations known to fully inhibit ERK5 (as referenced in papers in original comment), EMT signaling isn t regulated by ERK5. If adding a bromodomain inhibitor to an ERK5 inhibitor does something special that neither ERK5 inhibitor nor BRD inhibitor can do on its own, submit this observation to Nature Cell Science. , 
 Thank you for your comment. Like we mentioned earlier, ERK5 does play a role in EMT, as confirmed by us in siERK5 and ERK5 knockout models, as have other studies discussed in the review. We are further examining the effects of ERK5 and BRD4 inhibition on EMT alone and in combination. We like your suggestion of publishing these results in Nature Cell Science. Thanks. , 
 #6 Here s the distinction:  ERK5 signaling suggests the kinase function of ERK5 controls downstream biology by virtue of changing the phosphorylation state of a kinase, transcription factor, etc., but deleting the entire protein removes much more than ERK5 s kinase activity. Remember, ERK5 is also called Big MAP Kinase 1 due to its large size, and it includes non-kinase domains. If ERK5 inhibitors don t block a process but knocking down the entire protein does, some non-kinase function controls the process -- a non-signaling function. , 
 We also have data with more specific MEK5 ERK5 inhibitors that suggest a role for this pathway in EMT. That is not to say that inhibition of BRD4 will not synergize with the specific MEK5 ERK5 inhibitors, but our data clearly suggest a role for the ERK5 pathway in EMT. As we said above, these data are not included in this review as they are not yet published. We are aware of the different domains of ERK5 and our research will continue to distinguish between the roles of these unique domains of ERK5 in processes related to cancer. In conclusion, we have thoroughly answered your questions to the best of our ability. We can not answer for the research of others that are cited in the review. Thank you for your insight. ,