Ph.D Student Department of Internal Medicine II, University Hospital Würzburg, Germany Würzburg, Bayern, Germany
Introduction: Multiple myeloma (MM) is a bone marrow (BM) plasma cell malignancy. The tumor microenvironment (TME) contains cellular components as well as the non-cellular extracellular matrix (ECM). Previous research has shown that the expression level of the genes involved in the interaction between MM cells and TME is associated with patient survival. Changes in ECM also contribute to tumor progression and outcomes in patients. In MM, the ECM bidirectionally interacts with MM cells and co-inhabitants of tumor cells or metastatic niches. The oncogenic NOTCH signal has been confirmed to alter TME through contact-dependent signaling between ligands and receptors expressed on MM or stroma cells. However, whether the deregulation of NOTCH signaling affects genes controlling MM to dysregulate ECM integrity, improving clinical prognosis, is still unknown.
Methods: Here, we applied high-throughput transcriptome profiling to analyze gene expressions that are affected by impairing the NOTCH1 (N1) or NOTCH2 (N2) pathway in different MM cell lines. N1 and N2 knockdown was achieved by transducing corresponding shRNAs in RPMI 8226 and MM.1S cells.
Results: GO analysis revealed that N1 and N2 regulate core matrisome and matrisome-associated genes, including ECM affiliated protein, regulators, and secreted factors. Gene set enrichment analysis (GSEA) further indicated that both receptors (N1 and N2) control immune system-associated and cytokine activity signatures, such as cytokine receptor binding and inflammatory response in RPMI 8226 cells or leukocyte cell-cell adhesion, toll-like receptor signaling pathway, and chemoattractant activity in MM.1S cells. Moreover, N1/N2 depletion regulates genes involved in bone remodeling and resorption e.g., RUNX2 or SPP1. The 64 matrisome genes found to be consistently up- or downregulated under N1/N2 depletion in RPMI 8226 were further evaluated for the relation of ECM gene expression to patient survival in comparison with primary samples from monoclonal gammopathy of undetermined significance (MGUS), smoldering (sMM), untreated MM patients, and BM plasma (BMPC) of healthy donors. We showed that several ECM genes with expression levels related to the overall survival of MM patients are N2-driven targets, suggesting inhibition of NOTCH signaling might improve the clinical outcome in terms of overall survival.
Conclusions: Taken together, our data show that both NOTCH receptors participate in the transcriptional control of ECM glycoproteins, ECM-affiliated proteins, ECM regulators, and secreted factors that are proven to have prognostic significance in clinical settings. Further studies are required to better understand how changes in NOTCH-driven matrisome-associated proteins promote MM growth and dissemination in the BM niche.
