Introduction: thalidomide and the IMiDs in multiple myeloma

Extraosseous IL-6 transgenic mouse plasmacytoma sometimes lacks Myc-activating chromosomal translocation

The cellular oncogene MYC and plasma cell growth, differentiation, and survival factor IL-6 play critical roles in the natural history of human plasma cell neoplasms such as multiple myeloma (MM). Myc and IL-6 also are at the center of neoplastic plasma cell transformation in BALB/c mice that carry a human IL-6 transgene and, therefore, predictably develop plasmacytomas (PCTs). We showed previously that, much like advanced MM or human myeloma cell lines (HMCLs), in which MYC is frequently deregulated in cis because of complex cytogenetic aberrations juxtaposing MYC to immunoglobulin enhancers, IL-6 transgenic PCTs commonly deregulate Myc in cis by chromosomal translocation, predominantly T(12;15)(Igh-Myc). In this article, we show that, analogous to primary MM in which MYC is mostly deregulated in trans by signaling pathways converging at the MYC promoter, IL-6 transgenic PCTs sometimes develop in the absence of Myc translocations, thus activating Myc in trans. We present cytogenetic and molecular evidence on two IL-6 transgenic PCTs that contained overexpressed Myc protein but lacked T(12;15)(Igh-Myc) and two related Myc--deregulating translocations that juxtapose Myc to immunoglobulin light-chain instead of heavy-chain enhancers: T(6;15)(Igkappa-Pvt1) and T(15;16)(Pvt1-Iglambda). We conclude that Myc translocations are not strictly required for IL-6-driven PCT development in mice. IL-6 transgenic PCTs may provide a valuable model system for elucidating both trans and cis mechanisms of Myc deregulation of great relevance for MYC deregulation in human MM.