PRMT1 Sustains De Novo Fatty Acid Synthesis by Methylating PHGDH to Drive Chemoresistance in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) chemoresistance hampers the ability to effectively treat patients. Identification of mechanisms driving chemoresistance can lead to strategies to improve treatment. Here, we revealed that protein arginine methyltransferase-1 (PRMT1) simultaneously methylates D-3-phosphoglycerate dehydrogenase (PHGDH), a critical enzyme in serine synthesis, and the glycolytic enzymes PFKFB3 and PKM2 in TNBC cells. 13C metabolic flux analyses showed that PRMT1-dependent methylation of these three enzymes diverts glucose toward intermediates in the serine-synthesizing and serine/glycine cleavage pathways, thereby accelerating the production of methyl donors in TNBC cells. Mechanistically, PRMT1-dependent methylation of PHGDH at R54 or R20 activated its enzymatic activity by stabilizing 3-phosphoglycerate binding and suppressing polyubiquitination. PRMT1-mediated PHGDH methylation drove chemoresistance independently of glutathione synthesis. Rather, activation of the serine synthesis pathway supplied α-ketoglutarate and citrate to increase palmitate levels through activation of fatty acid synthase (FASN). Increased palmitate induced protein S-palmitoylation of PHGDH and FASN to further enhance fatty acid synthesis in a PRMT1-dependent manner. Loss of PRMT1 or pharmacologic inhibition of FASN or protein S-palmitoyltransferase reversed chemoresistance in TNBC. Furthermore, IHC coupled with imaging MS in clinical TNBC specimens substantiated that PRMT1-mediated methylation of PHGDH, PFKFB3, and PKM2 correlates with chemoresistance and that metabolites required for methylation and fatty acid synthesis are enriched in TNBC. Together, these results suggest that enhanced de novo fatty acid synthesis mediated by coordinated protein arginine methylation and protein S-palmitoylation is a therapeutic target for overcoming chemoresistance in TNBC. SIGNIFICANCE: PRMT1 promotes chemoresistance in TNBC by methylating metabolic enzymes PFKFB3, PKM2, and PHGDH to augment de novo fatty acid synthesis, indicating that targeting this axis is a potential treatment strategy.

Exposure to brefeldin A induces unusual expression of hybrid- and complex-type free N-glycans in HepG2 cells.

This study determined the effect of brefeldin A (BFA) on the free N-glycomic profile of HepG2 cells to better understand the effect of blocking intracellular vesicle formation and transport of proteins from the endoplasmic reticulum to the Golgi apparatus. A series of exoglycosidase- and endoglycosidase-assisted analyses clarified the complex nature of altered glycomic profiles. A key feature of BFA-mediated alterations in Gn2-type glycans was the expression of unusual hybrid-, monoantennary- and complex-type free N-glycans (FNGs). BFA-mediated alterations in Gn1-type glycans were characterized by the expression of unusual hybrid- and monoantennary-FNGs, without significant expression of complex-type FNGs. A time course analysis revealed that sialylated hybrid- and complex-type Gn2-type FNGs were generated later than asialo-Gn2-type FNGs, and the expression profiles of Gn2-type FNGs and N-glycans were found to be similar, suggesting that the metabolic flux of FNGs is the same as that of protein-bound N-glycans. Subcellular glycomic analysis revealed that almost all FNGs were detected in the cytoplasmic extracts. Our data suggest that hybrid-, monoantennary- and complex-type Gn2-type FNGs were cleaved from glycoproteins in the cytosol by cytosolic PNGase, and subsequently digested by cytosolic endo-ß-N-acetylglucosaminidase (ENGase) to generate Gn1-type FNGs. The substrate specificity of ENGase explains the limited expression of complex Gn1 type FNGs.

A rare case of eosinophilic gastritis induced by nivolumab therapy for metastatic melanoma.

Cancer immunotherapy using immune checkpoint inhibitors can cause immune reactions at various sites as a side effect called immune-related adverse events (irAEs). The gastrointestinal tract is susceptible to irAEs, however, the degree and presentation vary considerably from case to case. A 76-year-old woman was diagnosed with anal mucosal melanoma. She underwent radical surgery and received postoperative adjuvant therapy. However, because new metastases were also found in bilateral inguinal lymph nodes, immunotherapy with nivolumab was performed. Approximately 10 months after the initiation of nivolumab administration, she presented with epigastric discomfort and nausea, and her laboratory data showed severe eosinophilia (1938/mm3). Computed tomography demonstrated a diffuse thickening of the gastric wall. Esophagogastroduodenoscopy and endoscopic ultrasonography showed mucosal thickening due to edema, and histologic examination revealed severe invasion of eosinophils in the lamina propria. Subsequently, she was diagnosed with eosinophilic gastritis due to irAEs induced by nivolumab. Oral administration of prednisolone rapidly normalized her endoscopic and histologic findings, dramatically reducing her symptoms. This is a very rare and important case report of nivolumab-induced severe eosinophilic gastritis. Although gastric lesions as IrAEs is rare, it is necessary to differentiate eosinophilic gastritis if unexplained nausea occurred during the administration of immune checkpoint inhibitors.

Vitamin D Activates Various Gene Expressions, Including Lipid Metabolism, in C2C12 Cells.

Vitamin D is a fat-soluble molecule, well known for its role in regulating calcium homeostasis in bone. It has become increasingly clear that it also has important effects in many other organs, including the skeletal muscle. In order to gain insight into the role of vitamin D in the skeletal muscle, we performed microarray analysis using C2C12 myoblasts treated with 1,25-dihydroxyvitamin D (1,25(OH)2D), active form of vitamin D. We found multiple genes upregulated by 1,25(OH)2D. Some of them, i.e., vitamin D receptor (Vdr), diacylglycerol O-acyltransferase (Dgat1 and Dgat2, the rate limiting steps of triacylglycerol acylation), and vascular endothelial growth factor A (Vegfa), were previously reported to be upregulated by 1,25(OH)2D in C2C12 cells. RT-qPCR analysis confirmed increased mRNA levels of Rarres2, Dio2, Tgm2, Lpl, Mdfi, Igfbp3, Dgat1, Crabp2, Gadd45a, Vagfa, Dgat2, C3, Ldhb, Cebpa, Igfbp5, Mrc2, Vdr. Thus, many genes, including lipid metabolism genes as well as genes related to muscle functions, appear to be upregulated by 1,25(OH)2D in muscle cells.

A case of idiopathic portal hypertension accompanying multiple hepatic nodular regenerative hyperplasia in a patient with systemic sclerosis.

Idiopathic portal hypertension (IPH) is one of the background diseases causing nodular regenerative hyperplasia (NRH). Furthermore, IPH patients accompanied with autoimmune diseases, such as systemic lupus erythematosus (SLE) and systemic sclerosis (SSc), are more likely to form NRH in the liver. A 76-year-old woman had been aware of the Raynaud's phenomenon and scleroderma for the past 30 years. In this case, she presented with abdominal fullness, and her imaging analysis revealed ascites and multiple liver nodules. On Gd-EOB-DTPA enhanced magnetic resonance imaging (EOB-MRI), donut-like uptake was observed in the nodules in the hepatobiliary phase. Liver biopsy of a nodule demonstrated that it was composed of hyperplastic hepatocytes without fibrous septa, and dilated sinusoids were observed beside the nodule. Conversely, background liver showed that peripheral portal veins appeared stenotic with dense fibrosis in the portal area. The final diagnosis was that multiple NRH of the liver developed in SSc patient accompanying IPH. This case suggests that NRH may be unexpectedly diagnosed in patients with autoimmune diseases accompanying IPH.