JAM-A as a Prognostic Factor and New Therapeutic Target in Multiple Myeloma

Cell adhesion in the multiple myeloma (MM) microenvironment is a mechanism by which MM plasma cells escape the effects of therapy and survive. To improve clinical strategies and overcome drug resistance, approaches directed to both MMPCs and bone marrow microenvironment are under investigation. Here, we examined the cell membrane protein Junctional adhesion molecule-A (JAM-A) as a clinical biomarker and novel therapeutic target for MM. We evaluated JAM-A expression by real time PCR (RT-PCR), flow cytometry and immunofluorescence microscopy in 132 MM patients at different stages and various MM cell lines. Next, we measured the concentrations of soluble JAM-A from MM and healthy subjects sera by enzyme linked immune assay (ELISA). We investigated JAM-A functionally in vitro and in vivo by transient gene silencing (siRNA) and with blocking antibodies. Patient-derived plasma cells (MMPCs) expressed increased JAM-A expression levels when compared to control PC from healthy individuals. Elevated JAM-A expression correlated with poor prognosis (Figure 1A,B). Furthermore, soluble JAM-A was significantly increased in MM patient sera when compared to healthy subjects. Additionally, MM cell lines showed high expression of both membrane and cytoplasmic JAM-A. Consequently, inhibition of JAM-A using specific siRNA treatment resulted in diminished tumorigenic potential, including decreased colony formation, chemotaxis and migration. Importantly, treatment of luciferase+RPMI-8226 MM bearing NSG with a JAM-A blocking monoclonal antibody reduced significantly MM progression and dissemination in vivo when compared to MM bearing mice that received an non-specific isotype control antibody (Figure 1C). Conclusively, our data suggest that JAM-A can serve as a biomarker of malignancy in MM patients. Soluble plasma JAM-A could contribute to serum-based clinical stratification. Furthermore, therapeutic targeting of JAM-A appears attractive for clinical translation.