Crosstalk between PI3 kinase/PDK1/Akt/Rac1 and Ras/Raf/MEK/ERK pathways downstream PDGF receptor

Our plain-English summary of Crosstalk between PI3 kinase/PDK1/Akt/Rac1 and Ras/Raf/MEK/ERK pathways downstream PDGF receptor, by E.T. Niba, H. Nagaya, T. Kanno, et al (Cellular Physiology and Biochemistry, 2013).

The study

• Authors: E.T. Niba, H. Nagaya, T. Kanno, A. Tsuchiya, A. Gotoh, C. Tabata, K. Kuribayashi, T. Nakano, T. Nishizaki
• Journal: Cellular Physiology and Biochemistry
• Published: 2013;31(6):905-13
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background/aims: Our earlier studies suggested crosstalk between IRS/PI3 kinase/PDK1/Akt/Rac1/ROCK and (Shc2/Grb2/SOS)/Ras/Raf/MEK/ERK pathways downstream PDGF-ββ receptor responsible for chemotaxis and proliferation of malignant mesothelioma cells. The present study was conducted to obtain evidence for this.

Methods: To assess activation of Akt, MEK, and ERK, Western blotting was carried out on MSTO-211H malignant mesothelioma cells using antibodies against phospho-Thr308-Akt, phopho-Ser473-Akt, Akt, phospho-MEK, MEK, phopho-ERK1/2, and ERK1/2. To knock-down Akt, PI3 kinase, PDK1, and Rac1, siRNAs silencing each-targeted gene were constructed and transfected into cells. To monitor Rac1 activity, FRET monitoring was carried out on living and fixed cells.

Results: ERK was activated under the basal conditions in MSTO-211H cells, and the activation was prevented by inhibitors for PI3 kinase, PDK1, Akt, and Rac1 or by knocking-down PI3 kinase, PDK1, Akt, and Rac1. Akt was also activated under the basal conditions, and the activation was suppressed by a MEK inhibitor and an ERK1/2 inhibitor. In the FRET analysis, Rac1 was activated under the basal conditions, and the activation was inhibited by a MEK inhibitor and an ERK1/2 inhibitor.

Conclusion: The results of the present study show that ERK could be activated by PI3 kinase, PDK1, Akt, and Rac1 and that alternatively, Akt and Rac1 could be activated by MEK and ERK in MSTO-211H cells.

Copyright © 2013 S. Karger AG, Basel.

In plain English

This was a laboratory study of one human malignant mesothelioma cell line, MSTO-211H, grown in dishes. It did not study asbestos exposure or patients. The authors tested whether two internal signaling chains linked to a growth factor receptor (PDGF-ββ receptor) activate each other. They blocked individual signaling proteins with drugs or silenced their genes with siRNA. They then measured protein activation by Western blotting and Rac1 activity with a fluorescent (FRET) probe. The protein ERK was active in untreated cells. Its activity was reduced by blocking PI3 kinase, PDK1, Akt or Rac1, but the ROCK inhibitor Y27632 had no effect on it. Silencing Akt did not reduce activation of MEK. Akt activation was reduced by a MEK inhibitor (PD98059), by an ERK1/2 inhibitor (FR180204) and by silencing Rac1. The MEK and ERK inhibitors also reduced Rac1 activity. The text gave no numerical effect sizes; measurements were shown only in figures, from 4 independent Western blot experiments and 5 to 10 FRET experiments. The authors concluded that, in MSTO-211H cells, the two pathways can activate each other.

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 cell-culture experiment using drug inhibitors, siRNA gene silencing, Western blotting and FRET imaging of Rac1 activity
• Who was studied: MSTO-211H, a biphasic human malignant mesothelioma cell line purchased from American Type Culture Collection; no human subjects. Western blot experiments were n=4 independent experiments; FRET experiments were 6 (living cells) and 5-10 (fixed cells) independent experiments
• Exposure: No asbestos exposure was studied. Cells were treated with inhibitors: wortmannin 10 µM (PI3 kinase), BX912 100 nM (PDK1), MK2206 5 µM (Akt), NSC23766 1 µM (Rac1), Y27632 10 µM (ROCK), PD98059 50 µM (MEK) and FR180204 10 µM (ERK1/2). Separately, cells were given siRNAs silencing Akt, PI3 kinase, PDK1 or Rac1
• Main results:
  • In untreated MSTO-211H cells, ERK was active (phosphorylated) without any inhibitors
  • ERK activation was reduced by the Akt inhibitor MK2206. It was also reduced by inhibitors or gene silencing of PI3 kinase, PDK1 and Rac1. The text describes these effects in words; the measurements are shown only in figures
  • The ROCK inhibitor Y27632 had no effect on ERK activation
  • Silencing Akt did not reduce MEK activation, although it reduced ERK activation
  • Akt activation was reduced by the MEK inhibitor PD98059 and the ERK1/2 inhibitor FR180204
  • Silencing Rac1 reduced Akt activation
  • In fixed cells, Rac1 activity (measured as the FRET ratio) was reduced by the MEK inhibitor and the ERK1/2 inhibitor
• The authors' conclusion: The authors concluded that, in MSTO-211H cells, ERK could be activated through a PI3 kinase/PDK1/Akt/Rac1 pathway downstream of the PDGF-ββ receptor. They also concluded that Akt and Rac1 could be activated through the Ras/Raf/MEK/ERK pathway, meaning the two pathways cross-activate

Topics

Medical terms in this study, explained in our Lexicon: Platelet-Derived Growth Factor (PDGF), Malignant Mesothelioma.

Related studies

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• Group I p21-activated kinases (PAKs) promote tumor cell proliferation and survival through the AKT1 and Raf-MAPK pathways — C.W. Menges, E. Sementino, et al. (2012)
• Chrysotile asbestos upregulates gene expression and production of alpha-receptors for platelet-derived growth factor (PDGF-AA) on rat lung fibroblasts — J.C. Bonner, A.L. Goodell, et al. (1993)
• Upregulation of the PDGF-alpha receptor precedes asbestos-induced lung fibrosis in rats — J.A. Lasky, B. Tonthat, et al. (1998)
• Inhibition of phosphoinositide-3 kinase pathway down regulates ABCG2 function and sensitizes malignant pleural mesothelioma to chemotherapy — B. Fischer, C. Frei, et al. (2012)

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