Phospholipase C-related catalytically inactive protein regulates phosphatidyl-inositol metabolism and modulates cancer cell migration

[Speaker] Takashi Kanematsu:1
[Co-author] Satoshi Asano:1, Yosuke Yamawaki:1, Satoru Kusaka:1
1:Department of Cellular and Molecular Pharmacology, Institute of Biomedical and Health Sciences, Hiroshima University, Japan

The cellular phosphoinositide metabolism pathway and its metabolite signaling are important for numerous cellular processes. Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and its metabolite phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] are major signaling messengers, and dysfunctions in the control of PI(4,5)P2/PI(3,4,5)P3 signaling can often cause cancer. Activated PI(3,4,5)P3 pathways induce cancer cell growth and motility, resulting in enhanced cancer cell migration and invasion. Phospholipase C-related catalytically inactive protein (PRIP) is a protein that binds Ins(1,4,5)P3 or PI(4,5)P2 through its pleckstrin homology (PH) domain. There are two isoforms of PRIP in mammals, PRIP1 and PRIP2. It was reported that PRIP gene on chromosome 2q33 is homozygously deleted in human small cell lung carcinoma. Here, we investigated whether PRIP modulates cancer cell migration and invasion, and regulates PI(4,5)P2/PI(3,4,5)P3 signaling.
Scratch assay was performed to examine a migration activity of lung cancer cells expressing or lacking PRIP. Cancer cell migration activity and metastatic ability were analyzed using MCF-7 cells or BT-549 cells, breast cancer cell lines, in which EGFP-PRIP1 or empty vector plasmids were stably overexpressed. For investigating PRIP involvement in the modulation of PI(4,5)P2/PI(3,4,5)P3 signaling, mouse embryonic fibroblasts (MEFs) obtained from Prip-KO and wild-type mice were used for chemokinesis assays with PDGF.
Lung cancer cells lacking PRIP2 and/or PRIP1 displayed enhanced cell migration activity. Consistently, overexpression of PRIP1 in MCF-7 and BT-549 cells inhibited cell migration speed. PRIP-overexpressed BT-549 cells displayed suppressed metastatic ability in a tumor xenograft model. Prip-KO MEFs migrated greater than wild-type MEFs, but the difference of the migration activity became similar levels by silencing PI3K. The PDGF-stimulated PI(3,4,5)P3 production was greater in Prip-KO MEFs than in wild-type MEFs, and lamellipodium extension was enhanced in Prip-KO MEFs.

Our findings demonstrated that PRIP can regulate cancer cell migration activity in vitro and metastasis development in vivo. The novel tumor migration suppressor activity of PRIP was preferentially correlated with PI3K-PI(3,4,5)P3 production signaling. Hence, this new molecule regulating phosphoinositide metabolism is a potential therapeutic target for protection against metastatic progression.
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