Abstract
Binding of plasminogen type II (Pg 2) to dipeptidyl peptidase IV (DPP IV) on the surface of the highly invasive 1-LN human prostate tumor cell line induces an intracellular Ca2+ ([Ca2+]i) signaling cascade accompanied by a rise in intracellular pH (pHi). In endothelial cells, Pg 2 regulates intracellular pH via Na+/H+ exchange (NHE) antiporters; however, this mechanism has not been demonstrated in any other cell type including prostate cancer cells. Because the Pg 2 receptor DPP IV is associated with NHE3 in kidney cell plasma membranes, we investigated a similar association in 1-LN human prostate cancer cells and a mechanistic explanation for changes in [Ca2+]i or pHi induced by Pg 2 in these cells. Our results suggest that the signaling cascade initiated by Pg 2 and its receptor proceeds via activation of phospholipase C, which promotes formation of inositol 3,4,5-trisphosphate, an inducer of Ca2+ release from endoplasmic reticulum stores. Furthermore, our results suggest that Pg 2 may regulate pHi via an association with NHE3 linked to DPP IV in these cells. These associations suggest that Pg has the potential to simultaneously regulate calcium signaling pathways and Na+/H+ exchanges necessary for tumor cell proliferation and invasiveness.
Highlights
On the surface of human prostate tumor 1-LN cells [7], producing a rapid increase in [Ca2ϩ]i associated with expression of metalloproteinase-9, which in an in vitro model enhances the invasiveness of these cells [7]
Because IP3 is responsible for the release of calcium from calcium stores in the endoplasmic reticulum, we studied the effect of Pg 2 receptor activation on IP3 generation
We assessed the effect of inhibitors of phospholipase C (PLC), which hydrolyzes PIP2 into IP3 and diacylglycerol, on the rise of [Ca2ϩ]i induced by Pg 2 on 1-LN cells
Summary
Plasminogen; DPP IV, dipeptidyl peptidase IV; NHE, Naϩ/Hϩ exchange antiporter; IP3, inositol 3,4,5trisphosphate; PLC, phospholipase C; Val275–Val290, the NHE3 peptide sequence NH2-V275TRFTKHVRIIEPGFV290; HBSS, Hanks’ balanced salt solution; CELISA, cellular enzyme-linked immunosorbent assay; PBS, phosphate-buffered saline; BAPTA-AM, 1,2-bis (2-amino-5-fluorophenoxy)ethane-N,N,NЈ,NЈ-tetraacetic acid tetrakis (acetoxymethyl) ester; 6-AHA, 6-aminohexanoic acid. On the surface of human prostate tumor 1-LN cells [7], producing a rapid increase in [Ca2ϩ]i associated with expression of metalloproteinase-9, which in an in vitro model enhances the invasiveness of these cells [7]. Using this model, we recently demonstrated that a Pg fragment containing kringles 1–3 (angiostatin) is able to inhibit the Ca2ϩsignaling cascade induced by Pg via competition for binding to DPP IV [8]. These associations have the potential to regulate simultaneously calcium signaling pathways and Naϩ/Hϩ exchanges necessary for tumor cell invasiveness
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