Human BCL11B Is Expressed in Normal T Cells and Differentially Expressed in T-Cell Malignancies.

B-cell lymphomaleukaemia 11B (BCL11B), the human homologue of murine Bcl11b/Rit-1/CTIP2, was originally identified as a novel tumor suppressor gene in a study of gamma-radiation induced thymic lymphomas in mice. Later studies, however, showed Bcl11b to have a vital role in T cell development and survival, with BCL11B translocations involving a variety of partner genes being reported in both T-cell and myeloid leukemias. The human BCL11B gene, located at 14q32.2, encodes an 832aa Kruppel C2H2 zinc finger protein that is functionally uncharacterized but likely to act as a transcriptional regulator. Analysis of publically available normal tissue Affymetrix microarray expression data indicates an expression pattern restricted to hematopoietic cells, with high levels of BCL11B transcripts being present only in peripheral blood T cells, NK cells, thymus and tonsil.

We have used two rabbit polyclonal anti-BCL11B antibodies to study the distribution of BCL11B protein in both normal and neoplastic human cells. These reagents, raised against two distinct regions of the murine Bcl11b protein (zinc finger and C-terminus), recognized the human BCL11B protein. While neither antibody stained B-cells in tonsil, one was crossreactive with the highly homologous BCL11AXL protein by Western blotting. In normal tissues, BCL11B protein expression was confined to the nuclei of the vast majority of T cells in thymus (foetal and adult) and tonsil. High levels of BCL11B were detected in T-cell lines, including the Molt-4, CCRF-CEM and Jurkat T-cell acute lymphoblastic leukaemia (T-ALL) derived cell lines. No expression was detected in any B-cell derived (pre-B to plasma cell stage) or myeloid cell lines studied. These results are consistent with the microarray gene expression data. In T-cell malignancies, BCL11B protein was only detected in a proportion of tumors, including 5/6 T-ALLs (one being weakly stained) and 2/8 peripheral T-cell lymphomas (weak cytoplasmic staining only). Interestingly, no expression was detected in ALK-positive anaplastic large cell lymphoma lines or tumors. Further studies of a larger series of T-cell malignancies are in progress. All other tumors studied, including B-ALL, chronic lymphocytic leukaemia, diffuse large B-cell lymphoma, mantle cell lymphoma, Burkitt’s lymphoma, follicular lymphoma, myeloma and Hodgkin’s lymphoma, were unlabelled.

In conclusion, the distribution pattern of the BCL11B protein in a wide range of both normal and neoplastic tissues is described for the first time. The study of BCL11B expression is an invaluable first step towards elucidating the role of this protein in T-cell biology and the significance of its differential expression in T-cell malignancies.