CREB-induced inflammation is important for malignant mesothelioma growth

Our plain-English summary of CREB-induced inflammation is important for malignant mesothelioma growth, by C.M. Westbom, A. Shukla, M.B. MacPherson, et al (The American Journal of Pathology, 2014).

The study

• Authors: C.M. Westbom, A. Shukla, M.B. MacPherson, E.C. Yasewicz, J.M. Miller, S.L. Beuschel, C. Steele, H.I. Pass, P.M. Vacek, A. Shukla
• Journal: The American Journal of Pathology
• Published: 2014;184(10):2816-27
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is an aggressive tumor with no treatment regimen. Previously we have demonstrated that cyclic AMP response element binding protein (CREB) is constitutively activated in MM tumor cells and tissues and plays an important role in MM pathogenesis. To understand the role of CREB in MM tumor growth, we generated CREB-inhibited MM cell lines and performed in vitro and in vivo experiments. In vitro experiments demonstrated that CREB inhibition results in significant attenuation of proliferation and drug resistance of MM cells. CREB-silenced MM cells were then injected into severe combined immunodeficiency mice, and tumor growth in s.c. and i.p. models of MM was followed. We observed significant inhibition in MM tumor growth in both s.c. and i.p. models and the presence of a chemotherapeutic drug, doxorubicin, further inhibited MM tumor growth in the i.p. model. Peritoneal lavage fluids from CREB-inhibited tumor-bearing mice showed a significantly reduced total cell number, differential cell counts, and pro-inflammatory cytokines and chemokines (IL-6, IL-8, regulated on activation normal T cell expressed and secreted, monocyte chemotactic protein-1, and vascular endothelial growth factor). In vitro studies showed that asbestos-induced inflammasome/inflammation activation in mesothelial cells was CREB dependent, further supporting the role of CREB in inflammation-induced MM pathogenesis. In conclusion, our data demonstrate the involvement of CREB in the regulation of MM pathogenesis by regulation of inflammation.

Copyright © 2014 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.

In plain English

This was a laboratory study using human malignant mesothelioma (MM) cell lines and mice, not people. The authors studied CREB, a protein that switches genes on. They made two MM cell lines (HMESO and H2373) with CREB turned down. In dishes, these cells grew more slowly and were more sensitive to the chemotherapy drug doxorubicin. The authors injected HMESO cells under the skin or into the abdomen of immune-deficient (SCID) mice, 5 or 6 per group. The CREB-silenced cells formed significantly smaller tumors. Under the skin, median tumor volumes were 0.62172 in controls and 0.00052 in the CREB-silenced group (units not stated). Doxorubicin further reduced abdominal tumors. Abdominal fluid from mice with CREB-silenced tumors had fewer immune cells and lower levels of several inflammatory signals. In human mesothelial cells exposed to crocidolite asbestos, blocking CREB activation with a drug significantly reduced asbestos-induced inflammasome activation and the release of IL-1b and IL-18. The authors concluded that CREB-regulated inflammation may play a determining role in MM development and progression.

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: cell culture experiments plus mouse xenograft experiments (human MM cells injected into immune-deficient mice)
• Who was studied: Human MM cell lines (CREB-silenced HMESO and H2373; five MM lines in kinase-inhibitor tests), human peritoneal mesothelial LP9/TERT-1 cells, and 6-week-old Fox Chase SCID mice, 5 or 6 per group
• Exposure: CREB silencing or overexpression in MM cells. Crocidolite asbestos (NIEHS reference sample) added to mesothelial cells at a concentration printed as 5 mg/cm2. In the abdominal mouse model, doxorubicin was given at 0.5 mg/kg three times a week for 2 weeks.
• Main results:
  • In both MM cell lines, CREB silencing inhibited proliferation and increased sensitivity to doxorubicin in culture
  • Under-the-skin mouse model, after 45 days of growth: median tumor volumes were 0.62172 in the control (shCon) group and 0.00052 in the CREB-silenced (shCREB) group
  • CREB-silenced MM cells significantly reduced tumor growth in both the abdominal (i.p.) and under-the-skin (s.c.) mouse models
  • In the abdominal model, doxorubicin treatment further reduced tumor weights and volumes
  • CREB overexpression had no inhibitory effect on tumor weights and volumes in the abdominal model
  • In abdominal fluid, CREB inhibition alone and combined with doxorubicin decreased total immune cell numbers
  • CREB silencing reduced many human pro-inflammatory cytokines, chemokines and growth factors in abdominal fluid, including IL-6, IL-8, IP-10, MCP-1, MIP-1b, RANTES and VEGF
  • Doxorubicin treatment alone significantly increased levels of IL-6, IL-8, IP-10, MIP-1b and RANTES
  • In human mesothelial cells, blocking CREB activation with the inhibitor H89 significantly inhibited asbestos-induced NLRP3 inflammasome priming and activation
  • Secretion of IL-1b and IL-18 after asbestos exposure was also significantly reduced by CREB inhibition
  • No single kinase inhibitor blocked CREB activation in all five MM cell lines tested
  • CREB silencing lowered tumor-related genes in HMESO cells. The largest listed fold decrease was 23.16, for PAK7.
• The authors' conclusion: The authors concluded that CREB regulates MM tumor growth through many genes, and that CREB-regulated inflammation may play a determining role in MM development and progression
• Limitations the authors state:
  • Differences between the cell-death (TUNEL) staining and other stains may reflect staining done on different sections from different areas of the same tumor
  • IL-18 could not be measured in abdominal fluid because it was not part of the cytokine panel
  • Abdominal tumors grew attached to the mesentery, so individual tumors could not be counted

Topics

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

Medical terms in this study, explained in our Lexicon: Inflammation, Malignant Mesothelioma, Doxorubicin, Cytokine, Mesothelial Cells.

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