Autophagy facilitates the release of immunogenic signals following chemotherapy in 3D models of mesothelioma

Our plain-English summary of Autophagy facilitates the release of immunogenic signals following chemotherapy in 3D models of mesothelioma, by C. Follo, Y. Cheng, W.G. Richards, et al (Molecular Carcinogenesis, 2019).

The study

• Authors: C. Follo, Y. Cheng, W.G. Richards, R. Bueno, V.C. Broaddus
• Journal: Molecular Carcinogenesis
• Published: 2019;58(10):1754-1769
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We have previously shown that nearly half of mesothelioma patients have tumors with low autophagy and that these patients have a significantly worse outcome than those with high autophagy. We hypothesized that autophagy may be beneficial by facilitating immunogenic cell death (ICD) of tumor cells following chemotherapy. An important hallmark of ICD is that death of tumor cells is preceded or accompanied by the release of damage-associated molecular pattern molecules (DAMPs), which then can stimulate an antitumor immune response. Therefore, we measured how autophagy affected the release of three major DAMPs: high mobility group box 1 (HMGB1), ATP, and calreticulin following chemotherapy. We found that autophagy in three-dimensional (3D) models with low autophagy at baseline could be upregulated with the cell-permeant Tat-BECN1 peptide and confirmed that autophagy in 3D models with high autophagy at baseline could be inhibited with MRT 68921 or ATG7 RNAi, as we have previously shown. In in vitro 3D spheroids, we found that, when autophagy was high or upregulated, DAMPs were released following chemotherapy; however, when autophagy was low or inhibited, DAMPs release was significantly impaired. Similarly, in ex vivo tumors, when autophagy was high or upregulated, HMGB1 was released following chemotherapy but, when autophagy was low, HMGB1 release was not seen. We conclude that autophagy can be upregulated in at least some tumors with low autophagy and that upregulation of autophagy can restore the release of DAMPs following chemotherapy. Autophagy may be necessary for ICD in this tumor.

© 2019 Wiley Periodicals, Inc.

In plain English

This was a laboratory study of malignant pleural mesothelioma tumor cells grown as three-dimensional clusters. It did not study asbestos exposure. The authors used spheroids made from two mesothelioma cell lines, REN (low autophagy, a cell recycling process) and M28 (high autophagy), and tumor fragments from five patients who had not had chemotherapy before surgery. They raised autophagy with a peptide called Tat-BECN1, lowered it with MRT 68921 or ATG7 RNAi, and treated the cells with carboplatin plus pemetrexed. They measured cell death and the release of three 'danger signals' (HMGB1, ATP and calreticulin) that can alert the immune system. In low-autophagy spheroids, the signals appeared only when Tat-BECN1 was given with chemotherapy, and cell death increased. In high-autophagy spheroids, blocking autophagy reduced signal release. In the tumor fragments, Tat-BECN1 raised autophagy in all five. In the two low-autophagy tumors, HMGB1 was released after chemotherapy only with Tat-BECN1. The authors concluded that autophagy facilitates signal release and cell death after chemotherapy in these models. They noted that they did not show that the signals trigger an immune response.

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 of 3D models of mesothelioma: in vitro multicellular spheroids made from cell lines, and ex vivo tumor fragment spheroids made from resected patient tumors
• Who was studied: Two human mesothelioma cell lines (REN with low baseline autophagy, M28 with high baseline autophagy). Tumor tissue from five patients with malignant pleural mesothelioma who had surgery at Brigham and Women's Hospital in Boston without preoperative chemotherapy: three biphasic, one epithelioid, one epithelioid myxoid. Study dates are not given.
• Exposure: Chemotherapy with carboplatin (200 µM) plus pemetrexed (10 µM) for 16 or 24 hours. Autophagy was raised with the peptide Tat-BECN1 (10 µM) and lowered with MRT 68921 (1 µM) or ATG7 RNAi. No asbestos or fiber exposure was studied.
• Main results:
  • In REN spheroids (low baseline autophagy), Tat-BECN1 significantly increased autophagic flux. In M28 spheroids (high baseline autophagy), it did not increase autophagy further.
  • In low-autophagy spheroids, Tat-BECN1 significantly increased apoptosis (cell death) after chemotherapy. In high-autophagy spheroids, it did not increase apoptosis further. Apoptosis was seen at 24 hours of chemotherapy, not at 16 hours.
  • In low-autophagy spheroids, none of the three danger signals was evident at baseline, after chemotherapy alone, or after Tat-BECN1 alone. When Tat-BECN1 was given with chemotherapy, HMGB1 and ATP were released and calreticulin appeared on the surface of 12% of the cells.
  • In high-autophagy spheroids, all three signals were released after chemotherapy alone. Blocking autophagy with MRT 68921 significantly decreased HMGB1 and ATP release, and calreticulin was no longer detectable. With ATG7 RNAi, no HMGB1 release was seen.
  • In the five ex vivo tumor fragment spheroids (two with very low baseline autophagy, three with high), Tat-BECN1 significantly increased autophagy in all of them. ATG13 positivity was greater than 10% in every one afterwards.
  • In the two low-autophagy ex vivo tumors (TFS #1 and #2), chemotherapy alone did not increase apoptosis or cause HMGB1 release; with Tat-BECN1, both apoptosis and HMGB1 release after chemotherapy increased. In the three high-autophagy tumors (TFS #3 to 5), HMGB1 was released after chemotherapy alone and increased further with Tat-BECN1.
  • Release of the danger signals was seen after 16 hours of chemotherapy, before apoptosis was detected. The authors interpreted this as release before cell death.
• The authors' conclusion: The authors concluded that autophagy facilitates the release of danger signals (DAMPs) and cell death after chemotherapy in mesothelioma 3D models, and that low baseline autophagy could be upregulated to enhance immunogenic cell death.
• Limitations the authors state:
  • The study did not show that the release of the danger signals can stimulate an immune response.
  • Only one autophagy inducer (Tat-BECN1) was found to work in their system.
  • In the ex vivo tumors, only HMGB1 could be studied, because of technical difficulties measuring ATP and calreticulin.
  • The mechanism by which autophagy affects danger-signal release and cell death is unknown.

Topics

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

Medical terms in this study, explained in our Lexicon: Chemotherapy, Mesothelioma, High Mobility Group Box 1 (HMGB1).

Related studies

• Autophagy in 3D In Vitro and Ex Vivo Cancer Models — C. Follo, D. Barbone, et al. (2019)
• Asbestos induces mesothelial cell transformation via HMGB1-driven autophagy — J. Xue, S. Patergnani, et al. (2020)
• Inhibition of autophagy initiation potentiates chemosensitivity in mesothelioma — C. Follo, Y. Cheng, et al. (2018)
• Berberine induces mitochondrial‑mediated apoptosis and protective autophagy in human malignant pleural mesothelioma NCI‑H2452 cells — Z. Yao, Y. Wan, et al. (2018)
• Cisplatin and resveratrol induce apoptosis and autophagy following oxidative stress in malignant mesothelioma cells — Y.J. Lee, G.J. Lee, et al. (2016)
• Curcumin induces autophagy in ACC-MESO-1 cells — Y. Yamauchi, Y. Izumi, et al. (2012)

Browse more research in Molecular Carcinogenesis, or return to medical research.