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MEF2B is a member of the BCL6 gene transcriptional complex and induces its expression in diffuse large B-cell lymphoma of the germinal center B-cell-like type

Laboratory Investigation (2018) | Download Citation

Abstract

Myocyte enhancer-binding factor 2B (MEF2B) has been implicated as a transcriptional regulator for BCL6. However, details about the interaction between MEF2B and BCL6 during expression, as well as the relationship of MEF2B to the expression of other germinal center (GC) markers, have not yet been fully explained. Using germinal center B-cell-like diffuse large B-cell lymphoma (GC-DLBCL) and activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) cell lines, we analyzed the expression of MEF2B and its associations with BCL6, CD10, and ERK. Furthermore, small interfering RNA (siRNA) was used to study the possible effects of MEF2B knockdown on these proteins and cell growth. Analysis of the BCL6 transcriptional complex was performed using electrophoretic mobility shift assay. The correlation between MEF2B expression and the genetic type of DLBCL was assessed using immunohistochemistry on 111 patient samples, and via in silico analysis of publicly available microarray (Gene Expression Omnibus (GEO)) datasets. Our results indicate that the expression of MEF2B protein is important for the growth of GC-DLBCL cells, as evidenced by MEF2B knockdown inhibition of cell growth and the subsequent suppression of BCL6, CD10, and ERK phosphorylation. Analysis of BCL6 transcription factors in nuclear extracts of MEF2-expressing DLBCL cells showed involvement of MEF2B with AP-2α and BCL6 proteins in the formation of the BCL6 gene transcriptional complex. Indeed, differential expression of MEF2B in the GC-DLBCL is statistically significant compared to the ABC-DLBCL in the GEO datasets, as well as in tissue microarray, as indicated via immunohistochemistry (Visco–Young algorithm). Our findings indicate that MEF2B is an essential component of the BCL6 gene transcriptional complex for the regulation of DLBCL growth via the promotion of BCL6 expression. Beyond its regulatory role in DLBCL growth, MEF2B expression correlated positively with BCL6 and CD10 expression, and was preferentially expressed in the GBC-DLBCL group.

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Acknowledgements

This work was supported by grants from the German Research Foundation (HA 5081/3-1) and German Cancer Research Foundation (10-2202-Ha1) to M Hassan. We would like to thank Dr. Carols Cordon-Cardo at the Icahn School of Medicine at Mount Sinai for his support to this study. We would like to thank Dr. Francisco Vega at the University of Miami and Dr. Katia Basso at the Columbia University for providing some of the reagents, nuclear extracts, and MEF2B vectors required for this study. We would also like to thank Ms. Barbara Bishop, Ms. Denise Kelley, and Ms. Melissa Peak at Special Procedures Lab at the University of Louisville for performing the IHC stains.

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Affiliations

  1. Department of Pathology, Icahn School of Medicine at Mount Sinai, New York, NY, USA

    • Siraj M. El Jamal
    • , Julie Teruya-Feldstein
    •  & Adolfo Firpo-Betancourt
  2. Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA

    • Zakaria Grada
  3. Department of Medicine, University of Miami, Miami, FL, USA

    • Mohamed H. El Dinali
  4. Department of Surgery, Tulane University School of Medicine, New Orleans, LA, USA

    • He Zhou
    • , Helmi S. Khadra
    • , Jessica Friedman
    • , Hosam Shalaby
    •  & Mohamed Hassan
  5. Clinic of Dermatology, University Hospital of Aachen, Aachen, Germany

    • Sofie-Yasmin Hassan
    •  & Mosaad Megahed
  6. Department of Pathology, University of Tennessee Health Science Center and Le Bonheur Children’s Hospital, Memphis, TN, USA

    • Ali G. Saad
  7. Department of Pathology, University of Louisville, Louisville, KY, USA

    • Bradley Gibson
    •  & Mostafa Fraig
  8. Department of Pathology, University of Mississippi Medical Center, Jackson, MS, USA

    • Xinchun Zhou
  9. Department of Pediatrics, SUNY Downstate School of Medicine, Brooklyn, NY, USA

    • Hend A. Abulsayen
  10. Department of Pathology, Tulane University School of Medicine, New Orleans, LA, USA

    • Abida Kadi
  11. The Cancer and Blood Diseases Institute, Cincinnatti Children Hospital, Cincinnatti, OH, USA

    • Myesa Emberesh
  12. INSERM UMR 1121, University of Strasbourg, 67000, Strasbourg, France

    • Youssef Haikel
    •  & Mohamed Hassan
  13. Department of Operative Dentistry and Endodontics, Dental Faculty, University of Strasbourg, 67000, Strasbourg, France

    • Youssef Haikel

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The authors declare that they have no conflict of interest.

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Correspondence to Siraj M. El Jamal.

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DOI

https://doi.org/10.1038/s41374-018-0152-2