ERK2 is essential for the growth of human epithelioid malignant mesotheliomas

Our plain-English summary of ERK2 is essential for the growth of human epithelioid malignant mesotheliomas, by A. Shukla, J.M. Hillegass, M.B. MacPherson, et al (International Journal of Cancer, 2011).

The study

• Authors: A. Shukla, J.M. Hillegass, M.B. MacPherson, S.L. Beuschel, P.M. Vacek, K.J. Butnor, H.I. Pass, M. Carbone, J.R. Testa, N.H. Heintz, B.T. Mossman
• Journal: International Journal of Cancer
• Published: 2011;129(5):1075-86
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Members of the extracellular signal-regulated kinase (ERK) family may have distinct roles in the development of cell injury and repair, differentiation and carcinogenesis. Here, we show, using a synthetic small-molecule MEK1/2 inhibitor (U0126) and RNA silencing of ERK1 and 2, comparatively, that ERK2 is critical to transformation and homeostasis of human epithelioid malignant mesotheliomas (MMs), asbestos-induced tumors with a poor prognosis. Although MM cell (HMESO) lines stably transfected with shERK1 or shERK2 both exhibited significant decreases in cell proliferation in vitro, injection of shERK2 cells, and not shERK1 cells, into immunocompromised severe combined immunodeficiency (SCID) mice showed significant attenuated tumor growth in comparison to shControl (shCon) cells. Inhibition of migration, invasion and colony formation occurred in shERK2 MM cells in vitro, suggesting multiple roles of ERK2 in neoplasia. Microarray and quantitative real-time PCR analyses revealed gene expression that was significantly increased (CASP1, TRAF1 and FAS) or decreased (SEMA3E, RPS6KA2, EGF and BCL2L1) in shERK2-transfected MM cells in contrast to shCon-transfected MM cells. Most striking decreases were observed in mRNA levels of Semaphorin 3 (SEMA3E), a candidate tumor suppressor gene linked to inhibition of angiogenesis. These studies demonstrate a key role of ERK2 in novel gene expression critical to the development of epithelioid MMs. After injection of sarcomatoid human MM (PPMMill) cells into SCID mice, both shERK1 and shERK2 lines showed significant decreased tumor growth, suggesting heterogeneous effects of ERKs in individual MMs.

Copyright © 2010 UICC.

In plain English

This laboratory study used human malignant mesothelioma cell lines, grown in dishes and injected under the skin of immune-deficient (SCID) mice. It did not test asbestos exposure. The authors studied two related cell-signaling proteins, ERK1 and ERK2, using a drug (U0126) that blocks their activation, or by reducing each one's gene expression by about 80%. The drug slowed growth of the cell lines dose-dependently, while an inactive look-alike compound did not. In epithelioid HMESO cells, reducing either ERK1 or ERK2 slowed cell growth. Only reducing ERK2 lowered cell movement, invasion and growth in soft agar. Reducing ERK2 also changed mRNA levels of several genes, including a 38-fold drop in SEMA3E. In mice, tumors from ERK2-reduced HMESO cells grew significantly more slowly than controls. A second, 54-day experiment found significantly lower tumor sizes and growth at all time points. ERK1-reduced tumors' growth rate did not differ significantly. For a sarcomatoid line (PPMMill), the results section reports no tumor growth from either ERK-reduced line. The authors concluded that ERK1 and ERK2 play key roles in mesothelioma growth and suggested targeting ERKs in therapy.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study: experiments on human malignant mesothelioma cell lines in vitro, plus a mouse xenograft experiment (human tumor cells injected into SCID mice)
• Who was studied: Human pleural malignant mesothelioma cell lines: sarcomatoid MO, epithelioid ME-12, ME-26 and ME-27, epithelioid HMESO and sarcomatoid PPMMill. Immortalized human mesothelial cells (LP9/TERT-1) were used for comparison. 6-week-old Fox Chase SCID mice were used for tumor experiments (methods give N = 5 to 6 per group in duplicate experiments).
• Exposure: No asbestos exposure was studied. The experimental treatments were the MEK1/2 inhibitor U0126, which blocks phosphorylation (activation) of both ERK1 and ERK2 (applied at 10 and 20 µM, compared with its inactive analog U0124), and RNA silencing that reduced ERK1 or ERK2 expression, compared with scrambled controls.
• Main results:
  • In the stably transfected lines, ERK1 or ERK2 expression was reduced by 80%, and it stayed reduced after the cells were grown as tumors in mice.
  • In mesothelioma cell lines in vitro, U0126 inhibited growth in a dose-responsive way. The inactive analog U0124 did not.
  • In HMESO cells, both the ERK1-reduced and ERK2-reduced lines showed significant decreases in cell proliferation at 24, 48 and 72 hours compared with control cells.
  • In HMESO cells, only the ERK2-reduced line showed reduced migration, invasion and growth in soft agar (p less than 0.05).
  • Compared with control HMESO cells, microarrays found 875 gene expression changes (more than 2-fold, p less than 0.05) in ERK1-silenced cells and 789 in ERK2-silenced cells.
  • Some gene expression changes occurred only in ERK2-reduced HMESO cells: increases in CASP1, FAS and TRAF1, and decreases in SEMA3E, RPS6KA2, EGF and BCL2L1. SEMA3E expression was decreased 38-fold.
  • In the first HMESO mouse experiment (28 days), ERK2 reduction significantly attenuated tumor growth. The ERK2-reduced group's growth rate differed significantly from controls, but the ERK1-reduced group's did not.
  • In a second HMESO mouse experiment over 54 days, tumor sizes and growth were significantly lower in the ERK2-reduced group than in controls at all time points.
  • With sarcomatoid PPMMill cells followed for 7 weeks in mice, the results section reports no tumor growth from ERK1- or ERK2-reduced cells, unlike control cells.
• The authors' conclusion: The authors concluded that ERK1 and ERK2 have key roles in the growth and tumor formation of human mesotheliomas, possibly through distinct patterns of gene expression. They wrote that their results advocate targeting ERKs, alone or with chemotherapy drugs, in mesothelioma therapy.
• Limitations the authors state:
  • The ERK2-reduced HMESO tumors were too small and too few to compare proliferation, cell death and blood-vessel formation with the other groups.
  • Because the ERK-reduced PPMMill cells formed no tumors, further mechanistic studies and ERK RNA measurements in those tumors were not possible.
  • The growth-inhibiting effect of U0126 might be due to other targets, including ERK5, rather than ERK1 and ERK2.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Epithelioid, Malignant Mesothelioma, Carcinogenesis, Prognosis, Tumor Suppressor Gene, Angiogenesis, Sarcomatoid.

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• 3-O-Methylfunicone, a metabolite produced by Penicillium pinophilum, modulates ERK1/2 activity, affecting cell motility of human mesothelioma cells — E. Buommino, I. Paoletti, et al. (2010)
• Gefitinib targets EGFR dimerization and ERK1/2 phosphorylation to inhibit pleural mesothelioma cell proliferation — R.E. Favoni, A. Pattarozzi, et al. (2010)
• Inflammation precedes the development of human malignant mesotheliomas in a SCID mouse xenograft model — J.M. Hillegass, A. Shukla, et al. (2010)
• An extracellular signal-regulated kinase 2 survival pathway mediates resistance of human mesothelioma cells to asbestos-induced injury — A. Shukla, T.F. Barrett, et al. (2011)

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