Abstract B117: From Epitranscriptomic to Metabolic Switch: PCIF1-Driven m6Am Modification Rewires Macrophage Lactate Metabolism to Orchestrate the Pancreatic Cancer Immune Microenvironment

Abstract

Pancreatic cancer (PC) remains resistant to immune checkpoint inhibitors (ICIs) due to its profoundly immunosuppressive tumor microenvironment (TME), where tumor-associated macrophages (TAMs) predominantly adopt M2-like phenotypes. N6,2'-O-dimethyladenosine (m6Am) is a dynamic RNA modification at the messenger RNA (mRNA) cap structure, and phosphorylated CTD-interacting factor 1 (PCIF1, also known as CAPAM) is its sole methyltransferase. We first analyzed PCIF1 expression in PC patients from public single-cell RNA sequencing (scRNA-seq) datasets. We then generated a myeloid-specific Pcif1 knockout mouse model (Pcif1fl/fl; Lyz2Cre, termed Pcif1-MKO) and established Panc02 orthotopic and subcutaneous PC models. Tumor growth, immune infiltration, and macrophage polarization were assessed by flow cytometry, and mass cytometry (CyTOF) . m6Am sequencing (m6Am-seq) and ribosome profiling (Ribo-seq) were combined to identify PCIF1 targets. Extracellular acidification rate (ECAR) was measured by Seahorse XF analysis. We found that PCIF1 was highly expressed in PC patient CD14+/macrophage cells and correlated with poor response to PD-1 blockade. Myeloid-specific Pcif1 deletion significantly suppressed Panc02 tumor growth, increased M1 macrophage infiltration (F4/80+CD86+), and enhanced CD8+ T cell effector function. Mechanistically, PCIF1 catalyzed m6Am modification on malic enzyme 1 (ME1) mRNA, suppressing its translation efficiency. PCIF1 loss elevated ME1 protein, increased lactate production, and promoted M1 polarization. Conversely, PCIF1 overexpression reduced lactate accumulation, which relieved P60-mediated selective autophagic degradation of SOCS3, thereby suppressing M1 polarization and promoting immune escape. These findings establish a novel "RNA epigenetics–metabolism–autophagy" axis in which PCIF1/m6Am/ME1 signaling reprograms macrophage lactate metabolism to control SOCS3 stability and dictate M1/M2 polarization. Targeting PCIF1 or ME1 represents a promising strategy to reverse immunosuppression and enhance ICI efficacy in pancreatic cancer. This abstract was written with assistance from generative artificial intelligence.