USP5 motivates immunosuppressive microenvironment in multiple myeloma by activating STAT2-PFKFB4-mediated glycolysis

Glycolysis, a classic characteristic of cancer cells, can drive cancer progression by generating lactate, which play as a key immunosuppressive mediator. Currently, ubiquitin-specific proteases 5 (USP5) has been demonstrated to facilitate tumor cell survival in multiple myeloma (MM), whereas whether USP5 was involved in glycolysis-lactate production pathway and immunosuppressive microenvironment formation in MM remain unknown.

The gene and protein expression characteristics were assessed via qRT-PCR and western blot. MM cell survival was determined by CCK-8 and flow cytometry analysis. Glycolysis was evaluated by examining glucose uptake, lactate production and ATP level via corresponding kits. Tumor-associated macrophages polarization was tested via measurement of M1/M2-like macrophage markers using qRT-PCR and flow cytometry methods. Dual-luciferase reporter, chromatin immunoprecipitation and co-immunoprecipitation assays were conducted to verified molecular relationship. Xenograft model was used for verified cellular findings.

USP5 was abnormally overexpressed in MM patients and cell lines. Knockdown of USP5 could restrain MM cell survival and glycolysis activity, thus reducing lactate-mediated immunosuppressive M2-like macrophage polarization in vitro and in vivo, whereas overexpression of USP5 play opposite impacts. Mechanistically, USP5 could downregulate the ubiquitination modification of STAT to stabilize STAT2 protein, thus activating PFKFB4 transcription. Moreover, STAT2 could overturn the regulatory role of USP5 on MM cell survival, glycolysis and lactate-mediated immunosuppressive M2-like macrophage polarization.

These findings elucidated that USP5 served as a regulator of glycolysis-lactate to stimulate M2-like macrophage formation by regulating STAT2-PFKFB4 signaling, which supported that USP5 could be a viable therapeutic target of MM treatment.