LRRN4 and UPK3B are markers of primary mesothelial cells

Our plain-English summary of LRRN4 and UPK3B are markers of primary mesothelial cells, by M. Kanamori-Katayama, A. Kaiho, Y. Ishizu, et al (PloS One, 2011).

The study

• Authors: M. Kanamori-Katayama, A. Kaiho, Y. Ishizu, Y. Okamura-Oho, O. Hino, M. Abe, T. Kishimoto, H. Sekihara, Y. Nakamura, H. Suzuki, A.R. Forrest, Y. Hayashizaki
• Journal: PloS One
• Published: 2011;6(10):e25391
• Cited by: 75 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Mesothelioma is a highly malignant tumor that is primarily caused by occupational or environmental exposure to asbestos fibers. Despite worldwide restrictions on asbestos usage, further cases are expected as diagnosis is typically 20-40 years after exposure. Once diagnosed there is a very poor prognosis with a median survival rate of 9 months. Considering this the development of early pre clinical diagnostic markers may help improve clinical outcomes.

Methodology: Microarray expression arrays on mesothelium and other tissues dissected from mice were used to identify candidate mesothelial lineage markers. Candidates were further tested by qRTPCR and in-situ hybridization across a mouse tissue panel. Two candidate biomarkers with the potential for secretion, uroplakin 3B (UPK3B), and leucine rich repeat neuronal 4 (LRRN4) and one commercialized mesothelioma marker, mesothelin (MSLN) were then chosen for validation across a panel of normal human primary cells, 16 established mesothelioma cell lines, 10 lung cancer lines, and a further set of 8 unrelated cancer cell lines.

Conclusions: Within the primary cell panel, LRRN4 was only detected in primary mesothelial cells, but MSLN and UPK3B were also detected in other cell types. MSLN was detected in bronchial epithelial cells and alveolar epithelial cells and UPK3B was detected in retinal pigment epithelial cells and urothelial cells. Testing the cell line panel, MSLN was detected in 15 of the 16 mesothelioma cells lines, whereas LRRN4 was only detected in 8 and UPK3B in 6. Interestingly MSLN levels appear to be upregulated in the mesothelioma lines compared to the primary mesothelial cells, while LRRN4 and UPK3B, are either lost or down-regulated. Despite the higher fraction of mesothelioma lines positive for MSLN, it was also detected at high levels in 2 lung cancer lines and 3 other unrelated cancer lines derived from papillotubular adenocarcinoma, signet ring carcinoma and transitional cell carcinoma.

In plain English

This laboratory study searched for genes that mark mesothelial cells. It did not study asbestos exposure. The authors compared gene activity in mesothelium dissected from 200 mice with other mouse tissues. They found 460 probes (311 gene loci) more active in at least one mesothelium source, and only 48 of these in both sources. After further tests in mouse tissues, they measured four candidate markers, LRRN4, UPK3B, NKAIN4 and mesothelin (MSLN), in 45 human RNA samples. These included primary mesothelial cells from 2 donors, 16 mesothelioma, 10 lung cancer and 8 unrelated cancer cell lines. Among normal primary cells, LRRN4 was detected only in mesothelial cells, while MSLN and UPK3B also appeared in other cell types. MSLN was detected in 15 of the 16 mesothelioma lines, LRRN4 in 8 and UPK3B in 6. MSLN was also expressed in some lung and other cancer lines. NKAIN4 failed to validate as a human mesothelial marker. Antibodies against LRRN4 and UPK3B stained one human epithelial mesothelioma sample. The authors concluded that LRRN4 appeared the most specific mesothelial lineage marker but was detected in only 8 of the 16 mesothelioma lines.

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: gene expression microarrays, qRTPCR and in-situ hybridization in mouse tissues, followed by qRTPCR in human primary cells and cancer cell lines and immunostaining of a human mesothelioma sample
• Who was studied: Mesothelial and other tissues from 7-week-old male C57BL/6 mice (mesothelial tissue prepared from 200 mice); a panel of 45 human RNAs including normal lung tissue, primary lung cells, primary mesothelial cells from 2 donors, 16 mesothelioma cell lines, 10 lung cancer cell lines and 8 unrelated cancer cell lines; one human epithelial mesothelioma autopsy sample
• Exposure: No asbestos exposure was studied. The study measured expression of candidate mesothelial marker genes. In the human panel these were MSLN, UPK3B, NKAIN4 and LRRN4.
• Main results:
  • In mice, 460 probes (corresponding to 311 loci) were over-expressed in at least one mesothelium source compared with all other tissues. Only 48 were significant for both sources.
  • In mouse in-situ hybridization, two markers not previously linked to mesothelium, Nkain4 and Lrrn4, showed mesothelial staining.
  • Among human primary cells, LRRN4 was detected only in primary mesothelial cells.
  • Among human primary cells, MSLN was also detected in bronchial and alveolar epithelial cells, and UPK3B was also detected in retinal pigment epithelial cells and urothelial cells.
  • MSLN was detected in 15 of the 16 mesothelioma cell lines. In 13 of these, expression was higher than in primary mesothelial cells.
  • LRRN4 was detected in 8 of the 16 mesothelioma cell lines and UPK3B in 6. The authors suggested these markers are down-regulated or lost in cancer.
  • MSLN was not specific to mesothelioma. It was strongly expressed in the large cell lung carcinoma line T3M-10 and moderately in the lung adenocarcinoma line PC-14, and it was also found in several other unrelated cancer lines.
  • NKAIN4 did not validate as a marker of human mesothelium or mesothelioma.
  • In immunostaining of one human epithelial mesothelioma sample, mesothelial-specific signal was seen for all three antibodies used, with a pattern similar to the MSLN positive control.
  • There appeared to be no correlation with mesothelioma subtype. The cell lines included 7 epitheloid, 8 sarcomatoid and 1 biphasic.
• The authors' conclusion: The authors concluded that LRRN4 appears to be the most specific marker of the mesothelial lineage, but it was detected in only 8 of 16 mesothelioma cell lines. They suggested it may be lost during tumor progression or adaptation to cell culture. They stated they are exploring LRRN4 ELISA-based assays for detecting mesothelioma antigens in patient body fluids.
• Limitations the authors state:
  • Loss of LRRN4 in cell lines may reflect adaptation to cell culture rather than tumor progression.
  • The pleural and pericardial mouse sample may have been contaminated with B or plasma cells.
  • It is not yet known whether the markers are expressed in other rare mesothelial populations.
  • Whether loss of LRRN4 or UPK3B relates to later stage or poorer prognosis was not examined.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Mesothelioma, Environmental Exposure, Prognosis, Median Overall Survival, Mesothelium, Biomarker, Mesothelin.

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