Journal: International Journal of Molecular Sciences
Article Title: An Immune-Independent Mode of Action of Tacrolimus in Promoting Human Extravillous Trophoblast Migration Involves Intracellular Calcium Release and F-Actin Cytoskeletal Reorganization
doi: 10.3390/ijms252212090
Figure Lengend Snippet: ( A ): Schematic depicting of the inositol triphosphate receptor (IP3R), which is an intracellular Ca 2+ -release channel located on the membrane of the endoplasmic reticulum (ER), and which belongs to the same family of the ryanodine receptors (RyRs). The conserved and widely abundant immunophilin FKBP12, which is a primary receptor for the immunosuppressant actions of TAC (FK506), has been demonstrated to physiologically interact with the inositol 1,4,5-trisphosphate receptor (IP3R) via a leucyl-prolyl dipeptide epitope that structurally resembles TAC (FK506). Here, we are postulating that TAC binding to FKBP12, likely through its structural mimicry to dipeptide epitopes on the FKBP12, sequesters this immunophilin from the IP3R, thus structurally destabilizing the channel conducive to a spiked release of [Ca 2+ ]i from ER stores (arrow). Abbreviations: TAC (FK506): tacrolimus; IP3R: inositol triphosphate receptor; ER: endoplasmic reticulum. ( B ): Schematic depicting of the inositol triphosphate receptor (IP3R) [Ca 2+ ]i-release pathway in trophoblast cells. The illustration depicts a potential mechanism through which TAC may influence [Ca 2+ ]i-release along the IP3R pathway and its putative intracellular signal transduction pathways involved in F-actin cytoskeletal reorganization in trophoblast cells. [Ca 2+ ]i-release in trophoblasts is normally a function of the G-protein-coupled receptor (GPCR)-mediated activation of phospholipase C (PLC) and the membrane-bound PI3K (which produces inositol triphosphate (IP3)). IP3 is a ligand for the intracellular IP3R channel of the internal Ca 2+ stores of the endoplasmic reticulum (ER). It is postulated that TAC influences [Ca 2+ ]i-release via its binding to the immunophilin FKBP12, plausibly resulting in the destabilization of the ER’s IP3R [Ca 2+ ]i-release channels. The observation that TAC was unable to release [Ca 2+ ]i in trophoblast cells in the presence of the IP3R inhibitor 2-APB suggests a major role for this RYR channel in the presently proposed mode of action of TAC. This notion is also supported by the ability of TAC to release [Ca 2+ ]i in the presence of the PI3K inhibitor Wortmannin, and the PLC inhibitor U73122. Moreover, PLC activation can also lead to the production of diacylglycerol (DAG), which in turn activates protein kinase C (PKC), contributing to F-actin polymerization through the phosphorylation of a large library of intermediate targets of Ca 2+ binding proteins. Based on data obtained in the present study, it is presently unclear if TAC-induced [Ca 2+ ]i-release can influence the activation of a multitude of Ca 2+ -binding proteins involved in the F-actin polymerization through the PKC signaling pathway. Abbreviations: TAC (FK506): tacrolimus; GPCR: G-coupled protein receptor; PLC: phospholipase C; IP3: inositol (1,4,5)3-phosphate; IP3R: inositol triphosphate receptor; PI3K: phosphatidylinositol 3-kinase; PKC: protein kinase C.
Article Snippet: Tacrolimus (TAC, FK506) (10 ng/mL) (Cat# B415260, Toronto Research Chemicals, Toronto, ON, Canada) was dissolved in dimethyl sulfoxide (DMSO) HybriMax TM (Cat# D2650, Millipore Sigma) and administered to each culture according to an established protocol [ ].
Techniques: Membrane, Binding Assay, Transduction, Activation Assay, Phospho-proteomics