Journal: The Journal of Biological Chemistry
Article Title: Inhibitory effects of β-galactoside α2,6-sialyltransferase 1 on the Hippo pathway in breast cancer cells
doi: 10.1016/j.jbc.2025.110266
Figure Lengend Snippet: Schematic diagram of the proposed molecular mechanism for negative regulation of Hippo signaling via ST6GAL1. Various upstream cell membrane receptors of the Hippo pathway have been identified, including the RTKs ( e.g. , EGFR), GPCRs ( e.g. , LPAR4), and integrins ( e.g. , integrin α5β1). The RTK, GPCR, and integrin signals transduced by growth factors (GFs, e.g. , EGF), extracellular factors ( e.g. , LPA), and the extracellular matrix (ECM, e.g. , FN) can facilitate Hippo pathway effectors ( e.g. , PI3K and FAK) association, which promote LATS1/2-mediated regulation of YAP. In the cells with ST6GAL1 expression ( left ), the cell membrane receptors, such as EGFR, LPAR4, and integrin α5β1, are modified by α2,6-sialylation, which mediate the integrin β1–EGFR/LPAR4 complex formation and in turn facilitate their responses to EGF, LPA, and FN, respectively. These signalings inactivate LATS1/2 kinases or induce the dephosphorylation of YAP, finally leading to hypophosphorylated YAP (p-YAP S127). Hypophosphorylated YAP accumulates in the nucleus, where it can bind to various transcription factors (TFs, e.g. , TEAD family) to enhance the expression of target genes ( e.g. , ANKRD1 , CTGF , and CYR61 ) expression that promote cell adhesion, spreading, proliferation, migration, and metastasis. The Hippo signaling can be inhibited by the verteporfin (VP) inhibitor, which targets YAP-TEAD activity. In the ST6GAL1 deficiency cells ( right ), the N -glycans on cell membrane receptors are without α2,6-sialylation, which exhibit weak integrin β1–EGFR/LPAR4 complex formation and delayed responses to EGF, LPA, and FN stimulation and activate the LATS1/2 kinases and phosphorylate YAP on S127. The phosphorylated YAP (p-YAP S127) is retained in the cytoplasm, inhibiting YAP/TEAD-dependent transcription. The p of the red background represents the activation of related proteins, while gray background represents the inactivation. LATS, large tumor suppressor kinase; YAP, yes-associated protein; ST6GAL1, β-galactoside α2,6-sialyltransferase 1; RTK, receptor tyrosine kinase; EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; FN, fibronectin; GPCR, G protein–coupled receptor; GT, glycosyltransferase; LPA, lysophosphatidic acid; FAK, focal adhesion kinase.
Article Snippet: The experiments were performed using the following antibodies: Rabbit antibodies against p-YAP(S127) (#13008S), p-LATS1(T1079) (#8654S), LATS1 (#3477S), p-Src(Y416) (#2101S), p-FAK(Y397) (#8556S), FAK (#3285S), EGFR (#4267S), p-EGFR(Y1068) (#3777S), and integrin β1 (#9699S) were from Cell Signaling Technology; mouse mAb against GAPDH (#sc-365062), and β-actin (#sc-47778) were from Santa Cruz Biotechnology; mouse mAb against integrin α5 (610633) was from BD Biosciences; rabbit pAbs against LPAR4 (22165-1-AP) and mouse mAb against YAP (66900-1-Ig) were obtained from Proteintech; rabbit pAb against ST3GAL4 (NBP1-69565) was obtained from Novus Biologicals; mouse mAbs against FLAG (clone M2, #F3165) and Src (clone GD11, #05-184) were from Sigma; goat pAb against ST6GAL1 (AF5924) was from R&D Systems; mouse mAb against integrin β1 (P5D2) was from Developmental Studies Hybridoma Bank.
Techniques: Membrane, Expressing, Modification, De-Phosphorylation Assay, Migration, Activity Assay, Activation Assay
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