Bortezomib (Velcade/PS341), a proteasome inhibitor used in the treatment of multiple myeloma (MM), can inhibit activation of nuclear factor-κB (NF-κB), a family of transcription factors often deregulated and constitutively activated in primary MM cells. NF-κB can be activated via several distinct mechanisms, including the proteasome inhibitor–resistant (PIR) pathway. It remains unknown what fraction of primary MM cells harbor constitutive NF-κB activity maintained by proteasome-dependent mechanisms. Here, we report an unexpected finding that constitutive NF-κB activity in 10 of 14 primary MM samples analyzed is refractory to inhibition by bortezomib. Moreover, when MM cells were cocultured with MM patient-derived bone marrow stromal cells (BMSC), microenvironment components critical for MM growth and survival, further increases in NF-κB activity were observed that were also refractory to bortezomib. Similarly, MM-BMSCs caused PIR NF-κB activation in the RPMI8226 MM cell line, leading to increased NF-κB–dependent transcription and resistance to bortezomib-induced apoptosis. Our findings show that primary MM cells frequently harbor PIR NF-κB activity that is further enhanced by the presence of patient-derived BMSCs. They also suggest that this activity is likely relevant to the drug resistance development in some patients. Further elucidation of the mechanism of PIR NF-κB regulation could lead to the identification of novel diagnostic biomarkers and/or therapeutic targets for MM treatment. (Mol Cancer Res 2008;6(8):1356–64)

Colorectal cancer originates within immunologically complex microenvironments. To date, the benefits of immunotherapy have been modest, except in neoantigen-laden mismatch repair–deficient tumors. Approaches to enhance tumor-infiltrating lymphocytes in the tumor bed may substantially augment clinical immunotherapy responses. In this article, we report that proteolysis of the tolerogenic matrix proteoglycan versican (VCAN) strongly correlated with CD8⁺ T cell infiltration in colorectal cancer, regardless of mismatch repair status. Tumors displaying active VCAN proteolysis and low total VCAN were associated with robust (10-fold) CD8⁺ T cell infiltration. Tumor-intrinsic WNT pathway activation was associated with CD8⁺ T cell exclusion and VCAN accumulation. In addition to regulating VCAN levels at the tumor site, VCAN proteolysis results in the generation of bioactive fragments with novel functions (VCAN-derived matrikines). Versikine, a VCAN-derived matrikine, enhanced the generation of CD103⁺CD11c^hiMHCII^hi conventional dendritic cells (cDCs) from Flt3L-mobilized primary bone marrow–derived progenitors, suggesting that VCAN proteolysis may promote differentiation of tumor-seeding DC precursors toward IRF8- and BATF3-expressing cDCs. Intratumoral BATF3-dependent DCs are critical determinants for T cell antitumor immunity, effector T cell trafficking to the tumor site, and response to immunotherapies. Our findings provide a rationale for testing VCAN proteolysis as a predictive and/or prognostic immune biomarker and VCAN-derived matrikines as novel immunotherapy agents.