Alterations in CIITA constitute a common mechanism accounting for downregulation of MHC class II expression in diffuse large B-cell lymphoma (DLBCL)

Kelly A. Cycon, Lisa M. Rimsza, Shawn P. Murphy

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Abstract

Objective: Significant decreases in patient survival are associated with downregulation of major histocompatibility complex class II (MHC-II) antigen expression in diffuse large B-cell lymphoma (DLBCL). However, the molecular mechanisms responsible for decreased MHC-II expression in DLBCL are poorly defined. We therefore examined these mechanisms in established DLBCL cell lines. Materials and Methods: Human leukocyte antigen (HLA)-DR surface expression was examined by flow cytometry. Expression of the MHC-II genes and the MHC-II transcriptional activators class II transactivator (CIITA) and RFX was investigated by reverse transcriptase polymerase chain reaction. The integrity of the MHC-II genes was examined by polymerase chain reaction. Stable transfection assays were utilized to reconstitute CIITA expression. Results: Dramatic variations in the levels of cell surface HLA-DR expression were observed on the DLBCL cell lines. OCI-Ly10 cells lack HLA-DR and HLA-DQ expression due to homozygous deletions within the MHC-II locus on chromosome 6. Dyscoordinate downregulation of MHC-II β-chain expression in OCI-Ly3 cells mediates dramatic reductions of MHC-II surface expression. In SUDHL-4 and SUDHL-6 cells, expression of the MHC-II genes is coordinately reduced and quantitatively correlated with expression of the CIITA, the master regulator of MHC-II transcription. DB cells lack expression of CIITA and all of the MHC-II genes. Stable transfection of DB cells with CIITA expression vectors resulted in coordinate upregulation of MHC-II gene expression, which demonstrates the causal relationship between the lack of CIITA and MHC-II loss. Conclusions: These data demonstrate that downregulation of MHC-II expression occurs by multiple distinct mechanisms in DLBCL. However, decreases in CIITA expression appear to be the most prevalent mechanism.

Original languageEnglish (US)
Pages (from-to)184-194.e2
JournalExperimental Hematology
Volume37
Issue number2
DOIs
StatePublished - Feb 2009

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ASJC Scopus subject areas

  • Molecular Biology
  • Hematology
  • Genetics
  • Cell Biology
  • Cancer Research

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