Fig. 4: EMT-TFs and relative pathways in PDAC invasion kinetics.

EMT plasticity is maintained by continuous interchangeability between the epithelial phenotype, p-EMT, and c-EMT. PDAC cells lose EPCAM (EPCAM^—) when initiating the EMT program, at which point the cancer cells transform into EMT-PDAC cells. In PDAC cells, the EMT program is usually activated by EMT-TFs (single or multiple expression). In addition, the EMT program can also be activated by the downstream pathways of EMT-TFs, including Fascin, which is regulated by Slug; the Snail/HDAC1/HDAC2 complex, which is formed by Snail; ITGA3, regulated by the binding of ZEB1 to YAP1/TEAD. For EMT-TFs, the upstream signals are activated by glutamine depletion, hypoxia, inflammation (IL-22), circRTN4 and ZIP4. Glutamine depletion activate Slug by triggering MEK/ERK and p-eIF2α/ATF4; hypoxia is able to upregulate Twist; IL-22 activate Twist and ZEB1 by inducing the JAK/STAT3 pathway; ZIP4 promotes ZEB1 binding to YAP1/TEAD to form the upstream activator of ITGA3 via two routes, one is activating ZEB1 and the other is indirectly activating YAP1 by inhibiting miR-373, the inhibitor of LATS2; circRTN4 activates EMT-TFs (Slug, Twist, ZEB1, Snail) by stabilizing RAB11FIP1. In EMT-PDAC cells, the initiation of EMT program activates BMP2 signaling, which specifically upregulate Grem1 through upregulation of SMAD1/5/9 under the involvement of SMAD4. Grem1 promoted EMT-PDAC cell invasion by upregulating downstream Slug and Snail expression, meanwhile, it inhibites BMP signaling in neighboring PDAC cells to maintain their epithelial phenotype via paracrine. Direct contact between EMT-PDAC cells and myofibroblasts results in the reorganization of the plasma membrane protein ATP1A1 at the tumor-mesenchymal interface, which activates the NF-κB signaling by triggering Ca²⁺ oscillations in myofibroblasts, NF-κB signal stimulates the secretion of activin A by INHBA. Activin A upregulates Snail and ZEB1 in adjacent EMT-PDAC cells via paracrine secretion. Activin A itself also promotes activin A production and myofibroblast fibrosis (αSMA upregulation) by stimulating ACTA2 via an autocrine pattern. ACTA2 actin alpha 2, ATF4, activating transcription factor 4, ATP1A1 ATPase Na⁺/K⁺ transporting subunit alpha 1, BMP2, bone morphogenetic protein, c-EMT complete EMT, EMT epithelial-mesenchymal transition, EPCAM epithelial cell adhesion molecule, EMT-TFs EMT-related transcription factors, HDAC histone deacetylase, IL interleukin, INHBA inhibin subunit beta A, ITGA3 integrin α3, JAK janus kinase, LATS2 large tumor suppressor kinase 2, MAPK mitogen-activated protein kinase, MEK MAPK kinase, PDAC pancreatic ductal adenocarcinomas, p-EMT partial EMT, NF-κB nuclear factor kappa B, Slug snail family transcriptional repressor 2, Snail snail family transcriptional repressor 1, PDAC pancreatic ductal adenocarcinomas, p-eIF2α phosphorylated eukaryotic initiation factor 2α, PSC pancreatic stellate cell, RAB11FIP1 RAB11 family interacting protein 1, STAT3, signal transducer and activator of transcription 3, TFEB transcription factor EB, Twist twist family BHLH transcription factor 1, YAP1 yes-associated protein 1, Zeb zinc finger E-Box binding homeobox, ZIP4 solute carrier family 39 member 4.