Usp9x- and Noxa-mediated Mcl-1 downregulation contributes to pemetrexed-induced apoptosis in human non-small-cell lung cancer cells

Our plain-English summary of Usp9x- and Noxa-mediated Mcl-1 downregulation contributes to pemetrexed-induced apoptosis in human non-small-cell lung cancer cells, by J. Yan, N. Zhong, G. Liu, et al (Cell Death & Disease, 2014).

The study

• Authors: J. Yan, N. Zhong, G. Liu, K. Chen, X. Liu, L. Su, S. Singhal
• Journal: Cell Death & Disease
• Published: 2014;5(7):e1316
• Cited by: 65 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Pemetrexed, a folate antimetabolite, combined with cisplatin is used as a first-line therapy for malignant pleural mesothelioma (MPM) and locally advanced or metastatic non-small-cell lung cancer (NSCLC). Pemetrexed arrests cell cycle by inhibiting three enzymes in purine and pyrimidine synthesis that are necessary for DNA synthesis. Pemetrexed also promotes apoptosis in target cells, but little is known about its mechanism in cancer cells. We have previously shown that pemetrexed can result in endoplasmic reticulum (ER) stress, and it can lead to downstream apoptosis. In this study, we further elucidate this mechanism. Our data show that pemetrexed increases Noxa expression through activating transcription factor 4 (ATF4) and activating transcription factor 3 (ATF3) upregulation. Furthermore, pemetrexed induces apoptosis by activating the Noxa-Usp9x-Mcl-1 pathway. Inhibition of Noxa by small interfering RNA (siRNA) promotes Usp9x (ubiquitin-specific peptidase 9, X-linked) expression. Moreover, downregulation of the deubiquitinase Usp9x by pemetrexed results in downstream reduction of myeloid cell leukemia 1 (Mcl-1) expression. Mechanistically, Noxa upregulation likely reduces the availability of Usp9x to Mcl-1, thereby promoting its ubiquitination and degradation, leading to the apoptosis of neoplastic cells. Thus, our findings demonstrate that Noxa-Usp9x-Mcl-1 axis may contribute to pemetrexed-induced apoptosis in human lung cancer cells.

In plain English

This was a laboratory study of two human non-small-cell lung cancer cell lines, A549 and H1792. The authors treated the cells with pemetrexed, a chemotherapy drug used with cisplatin as a first-line treatment for malignant pleural mesothelioma and for locally advanced or metastatic non-small-cell lung cancer. The study did not involve asbestos, patients, or mesothelioma cells. Pemetrexed raised levels of the proteins ATF4, ATF3 and Noxa, and lowered the proteins Usp9x and Mcl-1. When the authors blocked Noxa, ATF4 or ATF3 with small interfering RNA, fewer cells died by apoptosis (programmed cell death). When they blocked Mcl-1 or Usp9x, more cells died. After pemetrexed, more Noxa and less Usp9x were bound to Mcl-1, and Mcl-1 carried more ubiquitin, a tag that marks proteins for breakdown. Blocking both Noxa and the related protein Puma did not reduce cell death further. The authors concluded that a Noxa–Usp9x–Mcl-1 pathway may contribute to pemetrexed-induced cell death in human lung cancer cells. They stated that why Usp9x falls after pemetrexed is unclear and that the exact mechanism needs more study.

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 experiment on human cancer cell lines: drug treatment, gene silencing with small interfering RNA, western blots, flow cytometry and immunoprecipitation
• Who was studied: Two human non-small-cell lung cancer cell lines, A549 and H1792, obtained from the American Type Culture Collection. No patients or mesothelioma cells were studied.
• Exposure: Pemetrexed, a folate antimetabolite chemotherapy drug that the article says is used with cisplatin as first-line therapy for malignant pleural mesothelioma and for locally advanced or metastatic non-small-cell lung cancer. The cells were treated for up to 48 hours. No asbestos or other fiber exposure was studied.
• Main results:
  • In both cell lines, Noxa protein increased after pemetrexed treatment.
  • Blocking Noxa with small interfering RNA reduced the proportion of pemetrexed-treated cells undergoing apoptosis.
  • Pemetrexed lowered Mcl-1, and blocking Mcl-1 increased pemetrexed-induced apoptosis. The authors read this as Mcl-1 loss speeding cell death.
  • Pemetrexed increased ATF4 and ATF3, and blocking ATF3 or ATF4 lowered the pemetrexed-induced rise in Noxa.
  • Blocking Noxa raised Usp9x levels.
  • Pemetrexed lowered Usp9x. Blocking Usp9x lowered Mcl-1 and increased markers of apoptosis.
  • In A549 cells, after pemetrexed more Noxa and less Usp9x were bound to Mcl-1.
  • Pemetrexed also raised the related protein Puma. Blocking Puma and Noxa together did not reduce apoptosis more than blocking either one alone.
• The authors' conclusion: The authors concluded that the Noxa–Usp9x–Mcl-1 axis may contribute to pemetrexed-induced apoptosis in human lung cancer cells, and that pemetrexed acts through multiple cell-death pathways.
• Limitations the authors state:
  • The authors stated that the mechanism by which pemetrexed lowers Usp9x is unclear and that the relationship among Noxa, Mcl-1 and Usp9x needs further exploration.
  • The authors stated that whether blocking extrinsic and intrinsic cell-death pathways at the same time can stop pemetrexed-induced apoptosis requires further investigation.

Topics

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

Medical terms in this study, explained in our Lexicon: Pemetrexed (Alimta), Apoptosis, Lung Cancer, Cisplatin, First-line Therapy, Pleural Mesothelioma.

Related studies

• Death receptor 5 and cellular FLICE-inhibitory protein regulate pemetrexed-induced apoptosis in human lung cancer cells — L. Su, G. Liu, et al. (2011)
• Molecular mechanism implicated in Pemetrexed-induced apoptosis in human melanoma cells — A. Buqué, J.S.H. Muhialdin, et al. (2012)
• Enhanced apoptosis by pemetrexed and simvastatin in malignant mesothelioma and lung cancer cells by reactive oxygen species-dependent mitochondrial dysfunction and Bim induction — K.E. Hwang, Y.S. Kim, et al. (2014)
• Vorinostat eliminates multicellular resistance of mesothelioma 3D spheroids via restoration of Noxa expression — D. Barbone, P. Cheung, et al. (2012)
• BAK and NOXA are critical determinants of mitochondrial apoptosis induced by bortezomib in mesothelioma — S. Busacca, A.D. Chacko, et al. (2013)
• Downregulation of Bcl-xL and Mcl-1 is sufficient to induce cell death in mesothelioma cells highly refractory to conventional chemotherapy — E. Varin, C. Denoyelle, et al. (2010)

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