PAF1/HIF1α axis rewires the glycolytic metabolism to fuel aggressiveness of pancreatic cancer.

BACKGROUND: PAF1/PD2 deregulation contributes to tumorigenesis, drug resistance, and cancer stem cell maintenance in Pancreatic Cancer (PC). Recent studies demonstrate that metabolic reprogramming plays a role in PC progression, but the mechanism is poorly understood. Here, we focused on examining the role of PAF1/PD2 in the metabolic rewiring of PC. METHODS: Cell lines were transfected with shRNAs to knockdown PAF1/PD2. Metabolic genes regulated by PAF1/PD2 were identified by qPCR/western blot, and metabolic assays were performed. Immunoprecipitations/ChIP were performed to identify PAF1/PD2 protein partners and confirm PAF1/HIF1α sub-complex binding to LDHA. RESULTS: PAF1 and LDHA showed progressively increased expression in human pancreatic tumor sections. Aerobic glycolysis genes were downregulated in PAF1-depleted PC cells. Metabolic assays indicated a decreased lactate production and glucose uptake in knockdown cells. Furthermore, PAF1/PD2 depletion showed a reduced glycolytic rate and increased oxidative phosphorylation by ECAR and OCR analysis. Interestingly, we identified that HIF1α interacts and co-localizes with PAF1, specifically in PC cells. We also observed that the PAF1/PD2-HIF1α complex binds to the LDHA promoter to regulate its expression, reprogramming the metabolism to utilize the aerobic glycolysis pathway preferentially. CONCLUSION: Overall, the results indicate that PAF1/PD2 rewires PC metabolism by interacting with HIF1α to regulate the expression of LDHA.

Cancer-Associated Fibroblast Induces Acinar-to-Ductal Cell Transdifferentiation and Pancreatic Cancer Initiation Via LAMA5/ITGA4 Axis.

BACKGROUND & AIMS: Pancreatic ductal adenocarcinoma (PDAC) is characterized by desmoplastic stroma surrounding most tumors. Activated stromal fibroblasts, namely cancer-associated fibroblasts (CAFs), play a major role in PDAC progression. We analyzed whether CAFs influence acinar cells and impact PDAC initiation, that is, acinar-to-ductal metaplasia (ADM). ADM connection with PDAC pathophysiology is indicated, but not yet established. We hypothesized that CAF secretome might play a significant role in ADM in PDAC initiation. METHODS: Mouse and human acinar cell organoids, acinar cells cocultured with CAFs and exposed to CAF-conditioned media, acinar cell explants, and CAF cocultures were examined by means of quantitative reverse transcription polymerase chain reaction, RNA sequencing, immunoblotting, and confocal microscopy. Data from liquid chromatography with tandem mass spectrometry analysis of CAF-conditioned medium and RNA sequencing data of acinar cells post-conditioned medium exposure were integrated using bioinformatics tools to identify the molecular mechanism for CAF-induced ADM. Using confocal microscopy, immunoblotting, and quantitative reverse transcription polymerase chain reaction analysis, we validated the depletion of a key signaling axis in the cell line, acinar explant coculture, and mouse cancer-associated fibroblasts (mCAFs). RESULTS: A close association of acino-ductal markers (Ulex europaeus agglutinin 1, amylase, cytokeratin-19) and mCAFs (α-smooth muscle actin) in LSL-KrasG12D/+; LSL-Trp53R172H/+; Pdx1Cre (KPC) and LSL-KrasG12D/+; Pdx1Cre (KC) autochthonous progression tumor tissue was observed. Caerulein treatment-induced mCAFs increased cytokeratin-19 and decreased amylase in wild-type and KC pancreas. Likewise, acinar-mCAF cocultures revealed the induction of ductal transdifferentiation in cell line, acinar-organoid, and explant coculture formats in WT and KC mice pancreas. Proteomic and transcriptomic data integration revealed a novel laminin α5/integrinα4/stat3 axis responsible for CAF-mediated acinar-to-ductal cell transdifferentiation. CONCLUSIONS: Results collectively suggest the first evidence for CAF-influenced acino-ductal phenotypic switchover, thus highlighting the tumor microenvironment role in pancreatic carcinogenesis inception.

Spt5 interacts genetically with Myc and is limiting for brain tumor growth in Drosophila.

The transcription factor SPT5 physically interacts with MYC oncoproteins and is essential for efficient transcriptional activation of MYC targets in cultured cells. Here, we use Drosophila to address the relevance of this interaction in a living organism. Spt5 displays moderate synergy with Myc in fast proliferating young imaginal disc cells. During later development, Spt5-knockdown has no detectable consequences on its own, but strongly enhances eye defects caused by Myc overexpression. Similarly, Spt5-knockdown in larval type 2 neuroblasts has only mild effects on brain development and survival of control flies, but dramatically shrinks the volumes of experimentally induced neuroblast tumors and significantly extends the lifespan of tumor-bearing animals. This beneficial effect is still observed when Spt5 is knocked down systemically and after tumor initiation, highlighting SPT5 as a potential drug target in human oncology.

Metabolic Rewiring and Stemness: A Critical Attribute of Pancreatic Cancer Progression.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive diseases with a poor 5-year survival rate. PDAC cells rely on various metabolic pathways to fuel their unlimited proliferation and metastasis. Reprogramming glucose, fatty acid, amino acid, and nucleic acid metabolisms contributes to PDAC cell growth. Cancer stem cells are the primary cell types that play a critical role in the progression and aggressiveness of PDAC. Emerging studies indicate that the cancer stem cells in PDAC tumors are heterogeneous and show specific metabolic dependencies. In addition, understanding specific metabolic signatures and factors that regulate these metabolic alterations in the cancer stem cells of PDAC paves the way for developing novel therapeutic strategies targeting CSCs. In this review, we discuss the current understanding of PDAC metabolism by specifically exploring the metabolic dependencies of cancer stem cells. We also review the current knowledge of targeting these metabolic factors that regulate CSC maintenance and PDAC progression.

Elevated PAF1-RAD52 axis confers chemoresistance to human cancers.

Cisplatin- and gemcitabine-based chemotherapeutics represent a mainstay of cancer therapy for most solid tumors; however, resistance limits their curative potential. Here, we identify RNA polymerase II-associated factor 1 (PAF1) as a common driver of cisplatin and gemcitabine resistance in human cancers (ovarian, lung, and pancreas). Mechanistically, cisplatin- and gemcitabine-resistant cells show enhanced DNA repair, which is inhibited by PAF1 silencing. We demonstrate an increased interaction of PAF1 with RAD52 in resistant cells. Targeting the PAF1 and RAD52 axis combined with cisplatin or gemcitabine strongly diminishes the survival potential of resistant cells. Overall, this study shows clinical evidence that the expression of PAF1 contributes to chemotherapy resistance and worse clinical outcome for lethal cancers.

PAF1 cooperates with YAP1 in metaplastic ducts to promote pancreatic cancer.

Acinar-to-ductal metaplasia (ADM) is a precursor lesion of pancreatic ductal adenocarcinoma (PDAC); however, the regulators of the ADM-mediated PDAC development and its targeting are poorly understood. RNA polymerase II-associated factor 1 (PAF1) maintains cancer stem cells leading to the aggressiveness of PDAC. In this study, we investigated whether PAF1 is required for the YAP1-mediated PDAC development and whether CA3 and verteporfin, small molecule inhibitors of YAP1/TEAD transcriptional activity, diminish pancreatic cancer (PC) cell growth by targeting the PAF1/YAP1 axis. Here, we demonstrated that PAF1 co-expresses and interacts with YAP1 specifically in metaplastic ducts of mouse cerulein- or KrasG12D-induced ADM and human PDAC but not in the normal pancreas. PAF1 knockdown (KD) reduced SOX9 in PC cells, and the PC cells showed elevated PAF1/YAP1 complex recruitment to the promoter of SOX9. The PAF1 KD reduced the 8xTEAD and SOX9 promoter-luciferase reporter activities in the mouse KC (KrasG12D; Pdx-1 Cre) cells and human PC cells, indicating that the PAF1 is required for the YAP1-mediated development of ADM and PC. Moreover, treatment with CA3 or verteporfin reduced the expressions of PAF1, YAP1, TEAD4, and SOX9 and decreased colony formation and stemness in KC and PC cells. CA3 treatment also reduced the viability and proliferation of PC cells and diminished the duct-like structures in KC acinar explants. CA3 or verteporfin treatment decreased the recruitment of the PAF1/YAP1 complex to the SOX9 promoter in PC cells and reduced the 8xTEAD and SOX9 promoter-luciferase reporter activities in KC and PC cells. Overall, PAF1 cooperates with YAP1 during ADM and PC development, and verteporfin and CA3 inhibit ADM and PC cell growth by targeting the PAF1/YAP1/SOX9 axis in vitro and ex vivo models. This study identified a regulatory axis of PDAC initiation and its targeting, paving the way for developing targeted therapeutic strategies for pancreatic cancer patients.