Calretinin Functions in Malignant Mesothelioma Cells Cannot Be Replaced by the Closely Related Ca2+-Binding Proteins Calbindin-D28k and Parvalbumin

Our plain-English summary of Calretinin Functions in Malignant Mesothelioma Cells Cannot Be Replaced by the Closely Related Ca2+-Binding Proteins Calbindin-D28k and Parvalbumin, by J. Wörthmüller, A. Oberson, V. Salicio, et al (International Journal of Molecular Sciences, 2018).

The study

• Authors: J. Wörthmüller, A. Oberson, V. Salicio, W. Blum, B. Schwaller
• Journal: International Journal of Molecular Sciences
• Published: 2018;19(12)
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Calretinin (CR; CALB2) belonging to the family of EF-hand Ca2+-binding proteins (CaBP) is widely used as a positive marker for the identification of human malignant mesothelioma (MM) and functionally was suggested to play a critical role during carcinogenesis of this highly aggressive asbestos-associated neoplasm. Increasing evidence suggests that CR not only acts as a prototypical Ca2+ buffer protein, i.e., limiting the amplitude of Ca2+ signals but also as a Ca2+ sensor. No studies have yet investigated whether other closely related CaBPs might serve as substitutes for CR's functions(s) in MM cells. Genetically modified MM cell lines with medium (MSTO-211H and ZL5) or low (SPC111) endogenous CR expression levels were generated that overexpress either CR's closest homologue calbindin-D28k (CB) or parvalbumin (PV), the latter considered as a "pure" Ca2+ buffer protein. After lentiviral shCALB2-mediated CR downregulation, in both MSTO-211H and ZL5 cells expressing CB or PV, the CR deficiency-mediated increase in cell death was not prevented by CB or PV. With respect to proliferation and cell morphology of SPC111 cells, CB was able to substitute for CR, but not for CR's other functions to promote cell migration or invasion. In conclusion, CR has a likely unique role in MM that cannot be substituted by "similar" CaBPs.

In plain English

This was a laboratory study of human malignant mesothelioma cells grown in culture. It did not study people, animals or asbestos exposure. The authors made three mesothelioma cell lines (MSTO-211H, ZL5 and SPC111) produce extra amounts of one of two related calcium-binding proteins, calbindin-D28k or parvalbumin. They then lowered the cells' own calretinin, another calcium-binding protein, using a virus-delivered genetic tool. In unmodified MSTO-211H and ZL5 cells, lowering calretinin reduced the number of living cells by about 50%. Neither added protein prevented this loss in those two lines. Parvalbumin gave no protection in any line, but the cells held only low amounts of it. In SPC111 cells, clones carrying calbindin-D28k survived better than unmodified cells, significantly in two of three clones. Calbindin-D28k also showed a physical interaction with FAK and septin 7, two proteins that calretinin binds. In initial experiments, calbindin-D28k did not increase cell migration or invasion. The authors concluded that calretinin likely has a unique role in mesothelioma that similar proteins cannot replace.

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 (in vitro) cell-culture experiment: rescue experiments in genetically modified human mesothelioma cell lines
• Who was studied: Three human malignant mesothelioma cell lines: MSTO-211H (obtained from the American Type Cell Collection), and ZL5 and SPC111 (obtained from the University Hospital of Zurich). No human subjects.
• Exposure: No asbestos or fiber exposure was studied. The cells were genetically modified to overexpress calretinin (CR), calbindin-D28k (CB), parvalbumin (PV) or GFP-tagged calretinin. Calretinin was then reduced with a lentivirus carrying an shRNA against CALB2, with a GFP-targeting shRNA used as the control.
• Main results:
  • In unmodified (parental) MSTO-211H cells, viable cells decreased by about 50% 96 hours after calretinin downregulation. A similar decrease of about 50% was seen in parental ZL5 cells.
  • Parvalbumin expression gave no protective effect in any of the three cell lines. Parvalbumin clones had much lower concentrations of calcium-binding sites (average 5 µM) than calbindin-D28k and calretinin clones.
  • In MSTO-211H cells expressing calbindin-D28k, viability was strongly decreased after calretinin downregulation. Calbindin-D28k had no visible effect on ZL5 cell viability.
  • All three SPC111 clones expressing calbindin-D28k showed increased viability compared with SPC111 wild-type cells after calretinin downregulation. The increase was statistically significant in clones CB1 and CB2.
  • In initial experiments, calbindin-D28k did not increase migration or invasion of SPC111 cells.
  • In SPC111 cells, calbindin-D28k co-localized with FAK at focal adhesions and physically interacted with FAK and septin 7, both known calretinin targets.
• The authors' conclusion: The authors concluded that calretinin likely has a unique role in malignant mesothelioma that cannot be substituted by similar calcium-binding proteins. They added that neither calbindin-D28k nor parvalbumin seemed able to rescue the effect of calretinin loss in the cell lines with mainly epithelioid morphology.
• Limitations the authors state:
  • Parvalbumin was expressed at low levels, which prevented a direct comparison with the calbindin-D28k and calretinin clones in terms of calcium-buffering capacity.
  • The authors could not unambiguously conclude that the improved survival of SPC111 calbindin-D28k clones came specifically from calbindin-D28k's calcium-sensor function, and stated that more experiments are needed.
  • Single-cell cloning was not successful for MSTO-211H cells.

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: Calretinin, Malignant Mesothelioma, Carcinogenesis, Neoplasm.

Related studies

• Modulation of Calretinin Expression in Human Mesothelioma Cells Reveals the Implication of the FAK and Wnt Signaling Pathways in Conferring Chemoresistance towards Cisplatin — J. Wörthmüller, V. Salicio, et al. (2019)
• The calcium binding protein calretinin is a selective marker for malignant pleural mesotheliomas of the epithelial type — V. Gotzos, P. Vogt, et al. (1996)
• Regulation of calretinin in malignant mesothelioma is mediated by septin 7 binding to the CALB2 promoter — W. Blum, L. Pecze, et al. (2018)
• Overexpression or absence of calretinin in mouse primary mesothelial cells inversely affects proliferation and cell migration — W. Blum, L. Pecze, et al. (2015)
• Calretinin is essential for mesothelioma cell growth/survival in vitro: a potential new target for malignant mesothelioma therapy? — W. Blum, B. Schwaller (2013)
• LIM-domain protein AJUBA suppresses malignant mesothelioma cell proliferation via Hippo signaling cascade — I. Tanaka, H. Osada, et al. (2015)

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