Hyaluronan and proteoglycan link protein 1 (HAPLN1) activates bortezomib-resistant NF-κB activity and increases drug resistance in multiple myeloma

Nuclear factor-kappa B (NF-kappa B) is a family of transcription factors that play a key role in cell survival and proliferation in many hematological malignancies, including multiple myeloma (MM). Bortezomib, a proteasome inhibitor used in the management of MM, can inhibit both canonical and noncanonical activation of NF-kappa B in MM cells. However, we previously reported that a significant fraction of freshly isolated MM cells harbor bortezomib-resistant NF-kappa B activity. Here, we report that hyaluronan and proteoglycan link protein 1 (HAPLN1) is produced in bone marrow stromal cells from MM patients, is detected in patients' bone marrow plasma, and can activate an atypical bortezomib-resistant NF-kappa B pathway in MM cells. We found that this pathway involves bortezomib-resistant degradation of the inhibitor of NF-kappa B (I kappa B alpha), despite efficient bortezomib-mediated inhibition of proteasome activity. Moreover, HAPLN1 can also confer bortezomib-resistant survival of MM cells. We propose that HAPLN1 is a novel pathogenic factor in MM that induces an atypical NF-kappa B activation and thereby promotes bortezomib resistance in MM cells.