The Role of Elevated HMGCS1-Ketogenesis in Multiple Myeloma Niche
2Research institute, Meir Medical Center, Israel
3Hematology Unit, Meir Medical Center, Israel
4Autoimmunity Laboratory, Meir Medical Center, Israel
5Orthopedics Department, Meir Medical Center, Israel
6Bioinformatics Unit, G.S.W. Faculty of Life Sciences, Tel Aviv University, Israel
7Sackler faculty of Medicine, Tel Aviv University, Israel
Background- Previously, we showed that multiple myeloma (MM) patients` mesenchymal stem cells (MM-MSCs) promote translation initiation (TI) dependent MM progression whereas healthy donors (ND-MSCs) do not. Proteomics demonstrated significant elevation ↑83FC in MM-MSCs` 3-Hydroxy-3-Methylglutaryl-CoA-Synthase-1 (HMGCS1) compared to ND-MSCs. HMGCS1 participates in the mevalonate pathway (MVA), transcription of pluripotency genes and production of ketone bodies (KB), including β-hydroxybutyrate (BHB). We aimed to characterize MM-MSCs` HMGCS1 significance to MM.
Methods- MM/ND-MSCs` HMGCS1 cytosolic/nuclear compartmentalization and HMGCR expression were assessed as prerequisites to transcription and MVA activation, respectively (immunoblotting). Secreted BHB was measured (colorimetric kit). Phenotype of BHB (Sigma) treated MM cells was assessed: ATP production (Seahorse), cell-count (trypan-blue), viability (PrestoBlue), migration (transwell), invasion (zymogram) and MAPKs/TI factors` expression (immunoblotting).
Results- HMGCS1 absence in nuclei and no detectable HMGCR rule-out transcriptional and MVA roles. However, we observed increased BHB secretion from MM-MSCs (↑260%; p<0.01). BHB supplementation increased MM cells` mitochondrial ATP production (↑32%; p<0.01), proliferation (↑60%; p=0.07), viability (↑50%; p<0.01) but had no effect on migration and invasion. Increased p-JNK and p-P38 (↑45-55%; p<0.05), p-eIF4GI TI factor (↑36%; p<0.05) but no change in p-ERK and p-eIF4E were registered.
Conclusions- MM-MSCs increased KB secretion may promote adjacent MM cells` energy production and proliferation coupled with critical redesign of cellular cap-independent TI (p-eIF4GI) and stress response (pJNK/pP38). These novel observations are consistent with KB`s role as an alternative energy source and signaling moieties in cancer. Additional conclusive experiments are ongoing. Positive results will prove the critical role of MM-niche ketogenesis and present novel anti-myeloma targets.