Proteomics reveals NNMT as a master metabolic regulator of cancer-associated fibroblasts

Abstract

High grade serous carcinoma (HGSC) has a poor prognosis primarily due to its early dissemination throughout the abdominal cavity. Genomic and proteomic approaches have provided snapshots of the proteogenomics of ovarian cancer (OvCa)1,2, but a systematic examination of both the tumor and stromal compartments is critical to understanding OvCa metastasis. We developed a label-free proteomic workflow to analyze as few as 5,000 formalin-fixed, paraffin embedded cells microdissected from each compartment. The tumor proteome was stable during progression from in situ lesions to metastatic disease; however, the metastasis-associated stroma was characterized by a highly conserved proteomic signature, prominently including the methyltransferase nicotinamide N-methyltransferase (NNMT) and several proteins it regulates. Stromal NNMT expression was necessary and sufficient for functional aspects of the cancer associated fibroblast (CAF) phenotype, including the expression of CAF markers and the secretion of cytokines and oncogenic extracellular matrix. Stromal NNMT expression supported OvCa migration, proliferation, and in vivo growth and metastasis. Expression of NNMT in CAFs led to a depletion of S-adenosyl methionine (SAM) and a reduction in histone methylation associated with widespread gene expression changes in the tumor stroma. This work supports the use of ultra-low input proteomics to identify candidate drivers of disease phenotypes. NNMT is a central, metabolic regulator of CAF differentiation and cancer progression in the stroma that may be therapeutically targeted.

High stromal nicotinamide N‐methyltransferase (NNMT) indicates poor prognosis in colorectal cancer

“…Recently, NNMT was reported as a master metabolic regulator of CAFs in ovarian cancer . However, the significance of NNMT in CRC stromal compartments is unknown.…”

“…Recently, NNMT was reported as a master metabolic regulator of CAFs in ovarian cancer. 4 However, the significance of NNMT in CRC stromal compartments is unknown. In this study, we applied a genomic data-mining strategy to explore the compartments of NNMT expression in CRC.…”

“…This activity produces a methyl sink in the form of 1‐MNA, leading to depletion of SAM and reduces the overall methylation potential of cells. NNMT mediates SAM depletion and attenuating histone methylation in various cells, including cancer cells, which resulted in the extensive gene expression changes in the tumor stroma. Besides, NNMT can promote the CRC cell growth and increase the resistance of CRC cells to 5‐fluorouracil through the 1‐MNA production .…”

“…Interestingly, NNMT has been considered as a novel and sensitive serum biomarker for CRC detection, outperforming the clinical significance of carcinoembryonic antigen (CEA) . However, it was recently reported that NNMT was expressed in stroma and served as a major metabolic regulator of ovarian cancer‐associated fibroblasts (CAF) . The tumor microenvironment is critical in the development and progression of CRC, and stromal signatures in different tumor types have been described in the earlier works with possible clinical significance .…”

“…4 The tumor microenvironment is critical in the development and progression of CRC, and stromal signatures in different tumor types have been described in the earlier works with possible clinical significance. 4,16 However, the relevant markers, especially key regulators, have been scarcely reported. NNMT is also expressed in the stroma of colorectal tissue, 4 but the clinical significance of the protein is unknown.…”