Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2022 Feb 1.
Published in final edited form as: J Invest Dermatol. 2021 Feb;141(2):250–252. doi: 10.1016/j.jid.2020.07.010

The melanocyte lineage factor miR-211 promotes BRAFV600E inhibitor resistance

Stephen M Ostrowski 1, David E Fisher 1
PMCID: PMC7850168  NIHMSID: NIHMS1621303  PMID: 33504438

Abstract

Resistance to targeted therapy and immunotherapy remains a major hurdle in improving care for patients with advanced melanoma. microRNAs play important roles in regulating gene networks involved in disease progression and resistance to therapy in cancer, including melanoma. miR-211 contributes to melanocyte and melanoma biology and has been implicated in targeted therapy resistance. In this issue, Lee et al. report a novel mechanism by which miR-211 promotes resistance to BRAFV600E inhibitor therapy via upregulation of the ERK5 signaling pathway.

Cutaneous melanoma is the third most common form of skin cancer. Its clinical importance is enhanced due to the high risk of metastatic progression and the poor prognosis of metastatic disease. Activating BRAF mutations (predominantly BRAFV600E) are oncogenic drivers in >50% of cutaneous melanomas. While targeted inhibition with BRAFV600E specific inhibitors (BRAFi), alone or in combination with MEK inhibitors, offers high response rates, intrinsic or acquired resistance leads to disease progression and death in almost all cases. Immunotherapy with anti-CTLA4 and anti-PD1 antibodies has transformed metastatic melanoma care, but this approach offers durable regressions in a minority of cases. Overall, better understanding of therapeutic resistance mechanisms may profoundly impact care of melanoma patients.

It has been demonstrated that dominant mechanisms of BRAFi resistance that occur can be broadly classified as: 1) Mitogen-activated protein kinase (MAPK) pathway reactivation via a variety of mechanisms including BRAF alternative splicing or amplification and acquisition/selection for NRAS activating mutation; 2) upregulation of the MITF transcription factor; 3) loss of PTEN or related pro-survival mechanisms; and 4) phenotype switching to a low-MITF/dedifferentiated epigenetic cell state. In particular, MITF upregulation has been shown to occur in up to 50% of tumors in patients treated with BRAFi (Boshuizen et al., 2018). MITF transcriptionally regulates numerous genes that are critical for melanocyte and melanoma function and survival, including cell cycle regulators and anti-apoptotic proteins such as BCL2, BCL2A1, and CDK2. It is thought that MITF upregulation may lead to therapy resistance through upregulation of these genes and associated pathways, but other mechanisms have not been fully delineated.

Several microRNAs have been shown to be important for melanoma survival, with miR-211 serving as a notable and well characterized example. miR-211 resides genomically within intron 6 of the TRPM1 gene. TRPM1 (also termed melastatin 1) was originally identified as a possible tumor suppressor protein in melanoma. TRPM1 and miR-211 were previously observed to be downregulated during melanoma formation and metastasis, and it has since been demonstrated that loss of miR-211, but not TRPM1, promotes melanoma invasion and metastasis through repression of genes that are centrally important to melanoma metastasis (Levy et al., 2010, Mazar et al., 2010). Levels of TRPM1 and miR-211 are directly regulated by MITF transcription factor, and miR-211 has been shown previously to be upregulated after BRAFi treatment via MITF upregulation and to play a role in BRAFi resistance (Diaz-Martinez et al., 2018, Lunavat et al., 2017). However, the downstream mechanism(s) by which miR-211 influences therapy resistance had not been elucidated.

Lee et al. report elegant studies that are designed to identify a novel mechanism by which miR-211 promotes tumor growth and regulates therapy resistance (Lee et al., 2020). They began their studies with a focus on the role of miR-211 in vivo using a tumor xenograft model. Overexpression of miR-211 strongly augmented the growth of xenografted A375 melanoma cells. In this setting, miR-211 did not lead to the strong metabolomic switch previously identified in vitro, suggesting that other pathways in the tumor microenvironment may be involved for the pro-tumorigenic miR-211 effect (Mazar et al., 2016). RNA sequencing of xenografted tumors showed strong enrichment of ERK5 signaling pathway genes in miR-211 expressing tumors. RNA immunopurification and sequencing analysis from miR-211 expressing tumors showed enrichment for potential ERK5 regulators such as BIRC2 and DUSP family phosphatases in mir-211 overexpressing cells.

The authors then utilized in vitro cell culture assays to test the functional role of these putative ERK5 regulators and to show that targeting of DUSP6 by overexpression of miR-211 leads to ERK5 activation. Conversely, DUSP6 overexpression abrogates the effect of miR-211 overexpression on tumor promotion in the in vivo xenograft model. Lee et al. also show that ERK5 is upregulated in vemurafenib resistant melanoma cells, and that miR-211 expression (as quantified by qPCR) correlates with vemurafenib resistance in a large panel of cells. Overall, these data implicate the miR-211/DUSP6/ERK5 axis as a novel regulator of BRAFi sensitivity.

ERK 5 (encoded by the MAPK7 gene) is a fascinating protein that consists of an N-terminal kinase domain with high homology to ERK2, and a C-terminal domain that allows for nuclear localization and transcriptional coactivation of target genes (Gomez et al., 2016). While some cytoplasmic substrates have been identified, ERK5 is thought to mediate most of its function in the nucleus, either through kinase activity or by acting as a transcriptional coregulator. Phosphorylation of ERK5 by MEK5 in the kinase activation domain not only allows catalytic activity, but also allows for autophosphorylation and nuclear translocation. ERK5 nuclear translocation can also be regulated in MEK5 independent fashion. Further work can delineate the effect of the miR-211/DUSP6 axis on ERK5 nuclear localization and determine the precise ERK5 kinase and/or transcriptional targets involved in mediating BRAFi resistance. ERK5 can be activated by numerous stress and growth factor pathways, including oncogenic BRAF stimulation. Importantly, ERK5 has emerged as a possible therapeutic target in BRAF and NRAS mutated melanoma (Adam et al., 2020, Benito-Jardon et al., 2019). The findings of Lee et al. provide further evidence regarding the role of ERK5 in therapy resistance, and also demonstrate a novel mechanism by which miR-211 (via DUSP6) regulates ERK5 and that may have broad relevance to melanoma therapy.

Another interesting future direction would be to further clarify the role of miR-211 in responsiveness to therapy. The work by Lee et al. suggests that miR-211 is elevated after BRAFi treatment, and it is likely that in this setting miR-211 upregulation occurs as a result of MITF induction. It is unclear if miR-211 plays a role in resistance in the setting of the de-differentiation/low-MITF phenotype which occurs after targeted therapy in some tumors. Further exploration of the role of miR-211 in different contexts of therapy resistance, and in particular in human patient samples, would help to characterize precise clinical scenarios in which miR-211 may modulate therapeutic resistance. Finally, there is a subset of BRAF/MEK inhibitor-treated patients who exhibit impressive long-term clinical responses. It would be interesting to understand whether the miR-211/DUSP5/ERK5 axis exhibits a distinct behavior in this setting.

Figure 1. miR-211 drives BRAFi resistance through DUSP6/ERK5 axis.

Figure 1.

Open in a new tab

Resistance to BRAFi inhibitor treatment in many cases is driven by upregulation of the MITF transcription factor. miR-211 is located genomically within intron 6 of the TRPM1 gene and TRPM1/miR211 are regulated transcriptionally by MITF. Lee et al. demonstrate that miR-211 targets DUSP6 to prevent its expression, leading to ERK5 activation which in turn drives proliferation and BRAFi resistance of A375 melanoma cells.

Clinical Implications.

  • BRAFV600E mutation is a common oncogenic driver in melanoma but targeted therapies such as BRAF/MEK inhibition suffer from near universal development of resistance.

  • ERK5 has been shown to be involved in targeted therapy resistance in several recent studies.

  • Lee et al. demonstrate a mechanism by which miR-211 regulates the expression of regulators of Erk5 to promote therapy resistance.

Acknowledgements

DEF grateful acknowledges grant support from NIH (5P01 CA163222, 1R01CA222871, R01AR072304, and 5R01 AR043369-22), the Melanoma Research Alliance, and the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation.

Footnotes

Conflict of Interest

Dr. Fisher has a financial interest in Soltego, Inc., a company that is developing SIK inhibitors for topical skin darkening treatments that might be used for a broad set of human applications. Dr. Fisher’s interests were reviewed and are managed by Massachusetts General Hospital and Partners Healthcare in accordance with their conflict of interest policies.

References

  1. Adam C, Fusi L, Weiss N, Goller SG, Meder K, Frings VG, et al. Efficient Suppression of NRAS-Driven Melanoma by Co-inhibition of ERK1/2 and ERK5 MAPK Pathways. J Invest Dermatol 2020. [DOI] [PubMed] [Google Scholar]
  2. Benito-Jardon L, Diaz-Martinez M, Arellano-Sanchez N, Vaquero-Morales P, Esparis-Ogando A, Teixido J. Resistance to MAPK Inhibitors in Melanoma Involves Activation of the IGF1R-MEK5-Erk5 Pathway. Cancer Res 2019;79(9):2244–56. [DOI] [PubMed] [Google Scholar]
  3. Boshuizen J, Koopman LA, Krijgsman O, Shahrabi A, van den Heuvel EG, Ligtenberg MA, et al. Cooperative targeting of melanoma heterogeneity with an AXL antibody-drug conjugate and BRAF/MEK inhibitors. Nat Med 2018;24(2):203–12. [DOI] [PubMed] [Google Scholar]
  4. Diaz-Martinez M, Benito-Jardon L, Alonso L, Koetz-Ploch L, Hernando E, Teixido J. miR-204-5p and miR-211-5p Contribute to BRAF Inhibitor Resistance in Melanoma. Cancer Res 2018;78(4):1017–30. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Gomez N, Erazo T, Lizcano JM. ERK5 and Cell Proliferation: Nuclear Localization Is What Matters. Front Cell Dev Biol 2016;4:105. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Lee B, Sahoo A, Sawada J, Marchica J, Sahoo S, Layng F, et al. MicroRNA-211 modulates the DUSP6-ERK5 signaling axis to promote BRAFV600E-driven melanoma growth in vivo and BRAF/MEK inhibitor resistance. J Invest Dermatol 2020. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Levy C, Khaled M, Iliopoulos D, Janas MM, Schubert S, Pinner S, et al. Intronic miR-211 assumes the tumor suppressive function of its host gene in melanoma. Mol Cell 2010;40(5):841–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Lunavat TR, Cheng L, Einarsdottir BO, Olofsson Bagge R, Veppil Muralidharan S, Sharples RA, et al. BRAF(V600) inhibition alters the microRNA cargo in the vesicular secretome of malignant melanoma cells. Proc Natl Acad Sci U S A 2017;114(29):E5930–E9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Mazar J, DeYoung K, Khaitan D, Meister E, Almodovar A, Goydos J, et al. The regulation of miRNA-211 expression and its role in melanoma cell invasiveness. PLoS One 2010;5(11):e13779. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Mazar J, Qi F, Lee B, Marchica J, Govindarajan S, Shelley J, et al. MicroRNA 211 Functions as a Metabolic Switch in Human Melanoma Cells. Mol Cell Biol 2016;36(7):1090–108. [DOI] [PMC free article] [PubMed] [Google Scholar]

RESOURCES