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3277 The c-MAF/SLP76 Axis Modulates Immune Evasion and Drives Malignancy in Multiple Myeloma Via Epigenetic Reprogramming

Program: Oral and Poster Abstracts
Session: 651. Multiple Myeloma and Plasma Cell Dyscrasias: Basic and Translational: Poster II
Hematology Disease Topics & Pathways:
Research, Fundamental Science
Sunday, December 8, 2024, 6:00 PM-8:00 PM

Zhenfeng Dai1*, Yunlu Jia2*, Jianbiao Zhou3*, Wee-Joo Chng, FRCP, FRCPath, PhD3 and Zhen Cai1*

1Bone Marrow Transplantation Center, Department of Hematology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
2Department of Medical Oncology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
3National University Cancer Institute of Singapore, Singapore, Singapore

Dysregulation of lineage-affiliated transcription factor expression represents a pivotal oncogenic mechanism, with c-MAF overexpression observed in approximately 50% of multiple myeloma (MM) cases, particularly associated with the adverse t(14;16) translocation subtype and poor prognosis. Despite c-MAF's known roles in immune regulation, its specific contribution to MM immune evasion remains unclear. This study aimed to elucidate the mechanisms underlying c-MAF-mediated immune dysregulation in MM and its therapeutic implications. Here, we found that persistent activation of c-MAF in MM is associated with T cell exhaustion in the bone marrow microenvironment. Specifically, co-culture experiments revealed that c-MAF activation in MM induced the expression of exhaustion markers PD-1, LAG-3, and TIGIT in T cells. To identify c-MAF-mediated downstream effectors modulating MM immune responses, we conducted a comparative transcriptome analysis between c-MAF-activated and c-MAF-normal MM cell lines, focusing on c-MAF-dependent transcriptional signatures. Based on correlation analysis with c-MAF expression levels in the transcriptome data of MM patients from the GEO database, we narrowed down the sets of c-MAF downstream genes and c-MAF-induced genes to 13 candidates (ITGB7, AHNAK, CCND2, SLP76, SLC37A4, TXNIP, TUBB, EI24, PRKCSH and NR2C2) and screened these to identify SLP76. SLP76 is a linker protein predominantly expressed in hematopoietic cells and plays a critical role in T cell receptor signaling pathways. Knockdown of SLP76 inhibits the expression of T cell exhaustion markers PD1, LAG3, and TIGIT, significantly enhances T cell killing capacity, inhibits cell proliferation, and induces apoptosis. Notably, in c-MAF-overexpressing cell lines, knockdown of SLP76 and c-MAF both induce degradation of PDL1, accompanied by suppression of the MAPK signaling pathway, including phosphorylated ERK and p38. The use of ERK or p38 inhibitors (STE-MEK1 or SB 202190) enhances the suppression of PDL1 by SLP76 knockdown. Given MAPK's role in PDL1 transcriptional upregulation, combined inhibition of SLP76 and MAPK signaling potentiated PDL1 suppression, suggesting a potential clinical translational direction for the combination of PDL1 immunotherapy and MAPK-targeted therapy in MM. Furthermore, clinical data suggest that SLP76 selectively promotes malignancy in c-MAF-activated multiple myeloma, strongly indicating the pathological significance of the c-MAF/SLP76 axis. Using multi-omics approaches including transcriptomic analysis, ChIP-seq and ATAC-seq to explore the upstream mechanisms of c-MAF regulation of SLP76, we found that persistent activation of c-MAF induces super-enhancer formation at the SLP76 gene locus. Direct binding of c-MAF to this super-enhancer region was observed in c-MAF-activated MM cell lines, accompanied by c-MAF-dependent accumulation of the active enhancer marker H3K27ac, BRD4 and MED1. Knockdown of c-MAF reduced H3K27ac deposition, indicating that c-MAF-mediated super-enhancer remodeling establishes the c-MAF-SLP76-PDL1 axis to modulate immune responses and drive MM malignancy. In summary, we demonstrate that c-MAF plays a non-canonical role in epigenetics, which is related to the regulation of cellular immune status, and suggest that immunotherapy combined with MAPK-targeted therapy represents a novel therapeutic direction for t(14;16) multiple myeloma.

Disclosures: Chng: Sanofi: Research Funding; GSK: Research Funding; Amgen: Honoraria; Janssen: Honoraria; BMS: Honoraria.

*signifies non-member of ASH