Abstract Collaboration of pro-inflammatory cytokine, interleukin 6 (IL-6), with oncogenic transcription factor, MYC, has been implicated in the natural history of human B-cell and plasma-cell neoplasms such as multiple myeloma (MM) and Waldenström's macroglobulinemia (WM). To generate a mouse model of IL-6/MYC-driven B-lineage tumors, we intercrossed strain C.H2-Ld-IL6 mice, which carry a human IL6 cDNA gene under control of the major histocompatibility complex (MHC) H2-Ld promoter, with strain C.iMycEμ and C.iMycCα mice, which harbor a gene-insertion mutation that recapitulates the chromosomal T(12;15) translocation leading to deregulated expression of MYC in mouse plasmacytoma (PCT). Double-transgenic C.IL6/iMycEμ and C.IL6/iMycCα mice develop PCT with full penetrance (100% tumor incidence), short latencies (3–6 months) and remarkable phenotypic consistency. To test the hypothesis that nuclear factor-κB (NF-κB) signaling plays a role in malignant plasma-cell transformation in these mice, we performed electrophoretic mobility shift assays (EMSA) using splenic B cells from C.IL6/iMycΔEμ mice. We found that the splenocytes contained elevated levels of NF-κB and signal transducer and activator of transcription 3 (STAT3) DNA-binding activities compared to normal splenic B cells used as control. Super-shift assays demonstrated that in addition to p50, p65 and c-Rel (indicators of canonical NF-κB pathway activation), RelB was involved. This suggested the additional activation of alternative NF-kB signaling. NF-kB, pSTAT3 and co-transcription factor, p300, were shown to be physically associated in transgenic B cells. Ongoing studies are aimed at elucidating whether NF-κB/STAT3/p300 signaling underlies up-regulation of c-myc level in the course of PCT development. Using qPCR we also found that p21 – which is usually known as a tumor suppressor and direct target of NF-κB, STAT3, p53 and MYC – exhibited increased p53-independent expression in B cells obtained from C.IL6/iMycΔEμ mice, but not from C.IL6 or iMycΔEμ mice. In contrast, the expression of Aurora kinase A, a direct upstream regulator of both NF-kB and E2F1, was strongly up-regulated in B cells from C.IL6/iMycΔEμ, C.IL6 and iMycΔEμ mice. Likewise, E2F1, a direct upstream regulator of p21, and E2F3, a direct upstream regulator of both p21 and Aurora kinase A, were upregulated. Our findings suggest that p21 is up-regulated, either directly or indirectly, through Aurora kinase A and/or NF-κB/STAT3/p300 complex. Furthermore, they indicate the usefulness of the newly developed IL-6/MYC mouse tumor model for identifying potential targets for the treatment and prevention of MM and WM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-48. doi:10.1158/1538-7445.AM2011-LB-48