B cell activator PAX5 promotes lymphomagenesis through stimulation of B cell receptor signaling
Diana Cozma, … , Michael L. Atchison, Andrei Thomas-Tikhonenko
Diana Cozma, … , Michael L. Atchison, Andrei Thomas-Tikhonenko
Published September 4, 2007
Citation Information: J Clin Invest. 2007;117(9):2602-2610. https://doi.org/10.1172/JCI30842.
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Research Article Oncology

B cell activator PAX5 promotes lymphomagenesis through stimulation of B cell receptor signaling

Abstract

The presumed involvement of paired box gene 5 (PAX5) in B-lymphomagenesis is based largely on the discovery of Pax5-specific translocations and somatic hypermutations in non-Hodgkin lymphomas. Yet mechanistically, the contribution of Pax5 to neoplastic growth remains undeciphered. Here we used 2 Myc-induced mouse B lymphoma cell lines, Myc5-M5 and Myc5-M12, which spontaneously silence Pax5. Reconstitution of these cells with Pax5–tamoxifen receptor fusion protein (Pax5ERTAM) increased neoplastic growth in a hormone-dependent manner. Conversely, expression of dominant-negative Pax5 in murine lymphomas and Pax5 knockdown in human lymphomas negatively affected cell expansion. Expression profiling revealed that Pax5 was required to maintain mRNA levels of several crucial components of B cell receptor (BCR) signaling, including CD79a, a protein with the immunoreceptor tyrosine-based activation motif (ITAM). In contrast, expression of 2 known ITAM antagonists, CD22 and PIR-B, was suppressed. The key role of BCR/ITAM signaling in Pax5-dependent lymphomagenesis was corroborated in Syk, an ITAM-associated tyrosine kinase. Moreover, we observed consistent expression of phosphorylated BLNK, an activated BCR adaptor protein, in human B cell lymphomas. Thus, stimulation of neoplastic growth by Pax5 occurs through BCR and is sensitive to genetic and pharmacological inhibitors of this pathway.

Authors

Diana Cozma, Duonan Yu, Suchita Hodawadekar, Anna Azvolinsky, Shannon Grande, John W. Tobias, Michele H. Metzgar, Jennifer Paterson, Jan Erikson, Teresa Marafioti, John G. Monroe, Michael L. Atchison, Andrei Thomas-Tikhonenko

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Figure 1

Contribution of Pax5 to neoplastic growth.

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Contribution of Pax5 to neoplastic growth. (A) Immunoblotting demonstrat...
(A) Immunoblotting demonstrating reactivation of Pax5 in 2 independent Myc5 tumors obtained from short-term cultures (T1 and T2) and lack of such reactivation in Myc5 tumors derived from long-term cultures (M5 and M12). Myc5 cultures engineered to overexpress Pax5 (Ctrl) were used as a positive control. (B) Myc5-M5 cells transduced with the Pax5 retrovirus maintain Pax5 expression in vivo (T5–T8). Vector-transduced cells were used as a negative control (T1–T4). (C) Pax5-transduced Myc5-M5 cells form more rapidly growing tumors than vector-transduced cells. Plotted on the y axis are average slope values. Error bars denote SD. In this and subsequent tumor load experiments, no less than 7 mice were used for each treatment group. (D) Flow cytometric analysis of representative tumors from C. Control tumors (left) were positive for the myeloid marker CD11b and negative for the B cell marker CD19. Pax5-transduced tumors (right) contain both CD11b–CD19– and CD11b–CD19+ cells. (E) Staining of formalin-fixed, paraffin-embedded sections with an antibody against B cell marker CD45R. Vector-transduced control tumors did not contain CD45R+ cells. Some Pax5-transduced tumors contain islets of CD45R+ cells (blue stain). Normal spleen was used as a positive control. Original magnification, ×4 (insets, ×20).