Upregulated expression and function of the α4β1 integrin in multiple myeloma cells resistant to bortezomib

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The interaction of multiple myeloma (MM) cells with the bone marrow (BM) microenvironment promotes MM cell retention, survival and resistance to different anti‐MM agents, including proteasome inhibitors (PIs) such as bortezomib (BTZ). The α4β1 integrin is a main adhesion receptor mediating MM cell‐stroma interactions and MM cell survival, and its expression and function are downregulated by BTZ, leading to inhibition of cell adhesion‐mediated drug resistance (CAM‐DR) and MM cell apoptosis. Whether decreased α4β1 expression and activity is maintained or recovered upon development of resistance to BTZ represents an important question, as a potential rescue of α4β1 function could boost MM cell survival and disease progression. Using BTZ‐resistant MM cells, we found that they not only rescue their α4β1 expression, but its levels were higher than in parental cells. Increased α4β1 expression in resistant cells correlated with enhanced α4β1‐mediated cell lodging in the BM, and with disease progression. BTZ‐resistant MM cells displayed enhanced NF‐κB pathway activation relative to parental counterparts, which contributed to upregulated α4 expression and to α4β1‐dependent MM cell adhesion. These data emphasize the upregulation of α4β1 expression and function as a key event during resistance to BTZ in MM, which might indirectly contribute to stabilize this resistance, as stronger MM cell attachment to BM stroma will regain CAM‐DR and MM cell growth and survival. Finally, we found a strong correlation between high ITGB1 (integrin β1) expression in MM and poor progression‐free survival (PFS) and overall survival (OS) during treatment of MM patients with BTZ and IMIDs, and combination of high ITGB1 levels and presence of the high‐risk genetic factor amp1q causes low PFS and OS. These results unravel a novel prognostic value for ITGB1 in myeloma.
This work was supported by grants SAF2014-53059-R and SAF2017-85146-R from the Ministerio de Ciencia, Innovación y Universidades (MCIU) to JT; SAF2017-89672-R from MCIU to FM; by the Research Institute Hospital 12 de Octubre (i+12) and grants from Instituto de Salud Carlos III (ISCIII) and CIBERONC to JML; by grants from ISCIII PI16/02024,PI17/00701 and PI19/01352, TRASCAN (EPICA and Immunocell), Fundació La Marató de TV3, the Accelerator award CRUK/AIRC/AECC joint funder-partnership, CIBERONC(CB16/12/00489) and co-financed with FEDER funds MINECO Explora (RTHALMY),Gobierno de Navarra, Departamento de Salud 40/2016 and Departamento de Industria (Proyecto Estrategico, Reto Genomica, DIANA) and Fundación Ramón Areces (PREMAMM) to FP and XA The study was also supported by the Multiple Myeloma Research Foundation Networks of excellence, the International Myeloma Foundation (Brian van Novis), and the Qatar National Research Fund award 7-916-3-237.