Identification of centerin: a novel human germinal center B cell-restricted serpin

Abstract

For naive B cells to mature in response to antigen triggering and become either plasma cells or memory B cells, a complex array of events takes place within germinal centers (GC) of secondary lymphoid organs. With the long‐term objective of defining and characterizing molecules that control the generation of GC, we have subtracted RNA messages derived from highly purified B cells at the follicular mantle stage of differentiation from GC B cells. Using this approach, we have identified a novel molecule, centerin, belonging to the family of serine‐protease inhibitors or serpins. Transcription of centerin is highly restricted to GC B cells and their malignant counterparts, Burkitt's lymphoma lines. The putative centerin protein shares the highest sequence identity with thyroxine‐binding globulin and possesses arginine / serine at its P1 / P1′ active site, suggesting that it interacts with a trypsin‐like protease(s). In addition, several other sequence features of centerin also indicate that it serves as a bonafide protease inhibitor. Finally, we demonstrate differentially up‐regulated transcription of this novel gene by resting, naive B cells stimulated in vitro via CD40 signaling, while Staphylococcus aureus Cowan strain‐mediated B cell activation fails to generate this reponse. Because CD40 signaling is required for naive B cells to enter the GC reaction and for GC B cells to survive, it is likely that centerin plays a role in the development and / or sustaining of GC.

Gcet1 (centerin), a highly restricted marker for a subset of germinal center-derived lymphomas

“…[1][2][3] The gene encoding Gcet1 is located on chromosome 14q32 and has been identified independently by 2 groups each using a different approach. First, mRNA was subtracted from highly purified GC B cells and demonstrated to be highly restricted to GC B cells and a selection of Burkitt lymphoma (BL) cell lines.…”

“…GCET1 was also demonstrated to be induced when naive B cells were stimulated in vitro via CD40 signaling, whereas Staphylococcus aureus Cowan strain activation failed to do so. 1 The second approach was based on the results from cDNA microarray analysis. A group of genes was identified as being highly expressed in normal GC B cells and GC B cell-derived malignancies, but not in resting or activated peripheral blood B cells.…”

“…[1][2][3] The gene is located on chromosome 14q32 and has 4 splicing isoforms, of which the longest (GCET1A) is 1787 bp in length and encodes a 435-amino acid protein. The Gcet1 primary amino acid sequence is homologous with the noninhibitory carrier protein TBG, with which it shares a 50% amino acid identity.…”

“…Northern blot studies revealed a restricted transcription to lymph node samples, the Burkitt-derived cell line Raji and HL-60 promyelocytic lines, and its absence from other normal tissues (including bone marrow, thymus, and spleen) and cancer cell lines. 1 We found no expression of Gcet1 in HL-60 and KG1 cell lines, which is consistent with the lack of expression of the gene in cells of myeloid lineage and with the findings of the TMA study of normal tissues, in which Gcet1 expression was limited to GC B cells.…”

Erratum: Comprehensive gene expression profiling and immunohistochemical studies support application of immunophenotypic algorithm for molecular subtype classification in diffuse large B-cell lymphoma: a report from the International DLBCL Rituximab-CHOP Consortium Program Study

“…39 In this scenario, GCET1 stains positive in rapidly dividing B-cells (i.e., Ki-67 + centroblasts) in the dark zone of the GC. Its expression is enhanced when B-cells are stimulated by CD40 signaling, 40 and it is then likely to identify centroblasts that have been rescued from cell death and are prompted to proliferate and undergo somatic hypermutation and class-switch recombination. 17,28,41 Foxp1 is an essential transcriptional regulator of B-cell development that influences B-cell development at very early stages, 42 and its mRNA expression is also typically elevated in ABC-DLBCL.…”