Abstract
<jats:title>Abstract</jats:title> <jats:p>More than 80% of multiple myeloma (MM) patients are diagnosed with pathological bone fractures or osteolysis. Currently, no therapeutic strategies focus on restoring bone-building osteoblast cells in patients with MM osteolytic lesions. Metabolic rewiring in MM displays high glutamine dependence or “addiction”, leading to glutamine depletion from the local niche, the bone. Notably, glutamine is essential for driving commitment and differentiation into bone-building osteoblasts to meet the high anabolic demands. The mechanism by which the glutamine-dependent osteoblast progenitor cells sense and respond to glutamine depletion by MM is unexplored. In this study, we demonstrate that the polyglutamine tract of the key osteoblast-differentiation transcription factor, Runt-related transcription factor 2 (RUNX2), serves as the molecular sensor that is exquisitely sensitive to glutamine depletion and consequently inhibits osteoblast differentiation in a glutamine-deprived bone niche developed by MM. We assessed osteoblast differentiation using growth assay, gene expression analysis, and differentiation staining assays. Nascent mRNA translation was measured using a fluorescent reporter-based assay and an on-membrane assay. These systems were analyzed under glutamine depletion, rerouting, or with MM cells. Our findings demonstrate that the polyglutamine tract senses a glutamine deficit resulting from the uncharging of glutamine tRNAs, leading to the suppression of translation of nascent RUNX2 mRNA and, consequently, osteoblast differentiation. Deletion or shortening of the polyglutamine tract renders RUNX2 insensitive to glutamine depletion. Supraphysiological RUNX2 in glutamine-depleted osteoblast progenitors compromises cell fitness, suggesting an adaptive function for this sensing mechanism. Furthermore, in osteoblast progenitors, rerouting glutamine towards anabolic pathways restores nascent RUNX2 translation and osteoblast differentiation under glutamine depletion. We found that MM cells suppress osteoblast differentiation, which can be restored by rerouting glutamine in osteoblast progenitors. These findings demonstrate that the critical transcription factor RUNX2 possesses an in-built glutamine sensor, the polyglutamine tract, which enables it to adapt and make cell fate decisions in response to glutamine deficit. Rerouting glutamine in osteoblast progenitors to make glutamine available for differentiation represents a novel therapeutic strategy to restore bone formation in the MM bone niche.</jats:p> <jats:sec> <jats:title>Citation Format:</jats:title> <jats:p>Mumtaz Shirin, Natalya N. Pavlova, . Rewiring glutamine metabolism restores osteoblast differentiation in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3280.</jats:p> </jats:sec>