Search

Fas ligation via the ligand FasL activates the caspase-8/caspase-3-dependent extrinsic death pathway. In so-called type II cells, an additional mechanism involving tBid-mediated caspase-9 activation is required to efficiently trigger cell death. Other pathways linking FasL-Fas interaction to activation of the intrinsic cell death pathway remain unknown. However, ATP release and subsequent activation of purinergic P2X(7) receptors (P2X(7)Rs) favors cell death in some cells. Here, we evaluated the possibility that ATP release downstream of caspase-8 via pannexin1 hemichannels (Panx1 HCs) and subsequent activation of P2X(7)Rs participate in FasL-stimulated cell death. Indeed, upon FasL stimulation, ATP was released from Jurkat cells in a time- and caspase-8-dependent manner. Fas and Panx1 HCs colocalized and inhibition of the latter, but not connexin hemichannels, reduced FasL-induced ATP release. Extracellular apyrase, which hydrolyzes ATP, reduced FasL-induced death. Also, oxidized-ATP or Brilliant Blue G, two P2X(7)R blockers, reduced FasL-induced caspase-9 activation and cell death. These results represent the first evidence indicating that the two death receptors, Fas and P2X(7)R connect functionally via caspase-8 and Panx1 HC-mediated ATP release to promote caspase-9/caspase-3-dependent cell death in lymphoid cells. Thus, a hitherto unsuspected route was uncovered connecting the extrinsic to the intrinsic pathway to amplify death signals emanating from the Fas receptor in type II cells., (Copyright © 2012 Wiley Periodicals, Inc.)

Tissue factor (TF) serving as the receptor for coagulation factor VII (FVII) initiates the extrinsic coagulation pathway. We previously demonstrated that progesterone increases TF, coagulation and invasion in breast cancer cell lines. Herein, we investigated if tissue factor pathway inhibitor (TFPI) could down-regulate progesterone-increased TF activity in these cells. Classically, TFPI redistributes TF-FVII-FX-TFPI in an inactive quaternary complex to membrane associated lipid raft regions. Herein, we demonstrate that TF increased by progesterone is localized to the heavy membrane fraction, despite progesterone-increased coagulation originating almost exclusively from lipid raft domains, where TF levels are extremely low. The progesterone increase in coagulation is not a rapid effect, but is progesterone receptor (PR) dependent and requires protein synthesis. Although a partial relocalization of TF occurs, TFPI does not require the redistribution to lipid rafts to inhibit coagulation or invasion. Inhibition by TFPI and anti-TF antibodies in lipid raft membrane fractions confirmed the dependence on TF for progesterone-mediated coagulation. Through the use of pathway inhibitors, we further demonstrate that the TF up-regulated by progesterone is not coupled to the progesterone increase in TF-mediated coagulation. However, the progesterone up-regulated TF protein may be involved in progesterone-mediated breast cancer cell invasion, which TFPI also inhibits., (Copyright © 2011 Wiley-Liss, Inc.)

Altered expression of some members of the TRP ion channel superfamily has been associated with the development of pathologies like cancer. In particular, TRPM4 levels are reportedly elevated in diffuse large B-cell non-Hodgkin lymphoma, prostate, and cervical cancer. However, whether such changes in TRPM4 expression may be relevant to genesis or progression of cancer remains unknown. Here we show that reducing TRPM4 expression decreases proliferation of HeLa cells, a cervical cancer-derived cell line. In this cell line, constitutive TRPM4 silencing promoted GSK-3β-dependent degradation of β-catenin and reduced β-catenin/Tcf/Lef-dependent transcription. Conversely, overexpression of TRPM4 in T-REx 293 cells (a HEK293-derived cell line) increased cell proliferation and β-catenin levels. Our results identify TRPM4 as an important, unanticipated regulator of the β-catenin pathway, where aberrant signaling is frequently associated with cancer.