Syndecan-1-Dependent Suppression of PDK1/Akt/Bad Signaling by Docosahexaenoic Acid Induces Apoptosis in Prostate Cancer

Abstract

Evidence indicates that diets enriched in n-3 polyunsaturated fatty acids (n-3 PUFAs) reduce the risk of prostate cancer, but biochemical mechanisms are unclear. Syndecan-1 (SDC-1), a transmembrane heparan sulfate proteoglycan, supports the integrity of the epithelial compartment. In tumor cells of epithelial lineage, SDC-1 is generally downregulated. This may result in perturbation of homeostasis and lead to progression of malignancy. Our studies have shown that the n-3 PUFA species, docosahexaenoic acid (DHA), increases SDC-1 expression in prostate tissues of Pten knockout (Pten(P-/-)) mice/cells and human prostate cancer cells. We have now determined that DHA-mediated up-regulation of SDC-1 induces apoptosis. Bovine serum albumin-bound DHA and exogenous human recombinant SDC-1 ecotodomain were delivered to PC3 and LNCaP cells in the presence or absence of SDC-1 small interfering (si)RNA. In the presence of control siRNA, both DHA and SDC-1 ectodomain induced apoptosis, whereas SDC-1 silencing blocked DHA-induced but not SDC-1 ectodomain-induced apoptosis. Downstream effectors of SDC-1 signaling linked to n-3 PUFA-induced apoptosis involved the 3'-phosphoinositide-dependent kinase 1 (PDK1)/Akt/Bad integrating network. A diet enriched in n-3 PUFA decreased phosphorylation of PDK1, Akt (T308), and Bad in prostates of Pten(P-/-) mice. Similar results were observed in human prostate cancer cells in response to DHA and SDC-1 ectodomain. The effect of DHA on PDK1/Akt/Bad signaling was abrogated by SDC-1 siRNA. These findings define a mechanism by which SDC-1-dependent suppression of phosphorylation of PDK1/Akt/Bad mediates n-3 PUFA-induced apoptosis in prostate cancer.

Docosahexaenoic Acid Induces Cell Death through Downregulation of Hedgehog Signaling via Surt6 Activation in Human EGFR Mutant Non-Small Cell Lung Cancer

“…Several studies have suggested that DHA exerts anticancer effects by inducing apoptotic cell death, and several signaling pathways have been reported to be involved in this process [30,31]. In the present study, we report for the first time that DHA-induced apoptosis in human EGFR mutant NSCLC is associated with the ability of DHA to trigger SIRT6 activation, which results in downregulation of Hh signaling ( Figure 6).…”

Docosahexaenoic acid inhibits the phosphorylation of STAT3 and the growth and invasion of renal cancer cells

“…Propidium-iodide (PI)-stained nuclear fractions were obtained and cell cycle data were acquired with a flow cytometer using CellQuest ™ software, version 5.2.1 (BD Biosciences, Franklin Lakes, NJ, USA), following the manufacturer's protocol. Percentages of apoptotic cells were also determined with a fluorescein isothiocyanate-conjugated Annexin V/PI double-staining assay, using an Annexin V Apoptosis Detection kit (Santa Cruz Biotechnology, Inc., Dallas, TX, USA), as described previously (21).…”

“…Cells were seeded at 0.3x10 6 in a 6 well flat bottom plate (IWAKI, Co., Ltd., Hong Kong, China) with MEM (1X) with 10% FBS and RPMI 1640 (1X) with 10% FBS for Caki-1 and 786-O cells, respectively. A wound was then made by scraping the middle of the cell monolayer with a P200 pipette tip, as previously described (21). After floating cells were removed following an extensive wash with 1 ml ice-cold phosphate-buffered saline, fresh complete MEM and RPMI medium supplemented with DHA was added to each type of cell, as previously detailed.…”

“…Cell invasion was evaluated using a Matrigel-coated Transwell system in 24-well plates including a membrane with 8-µm pores (BD Biosciences), as described previously (21). Briefly, 2x10 5 cells suspended in 500 µl serum-free medium (MEM and RPMI, as previously detailed) were added to the insert and 750 µl serum-free medium with the indicated concentration of DHA (0, 25, 50 and 100 µM) was added to the bottom of the well.…”

“…Cells at a density of 2x10 6 were treated with 0 (control), 50 and 100 µM DHA for 6 h, then lysed in radioimmunoprecipitation assay buffer composed of 10 mM tris-HCl (Nacalai Tesque, Inc., Kyoto, Japan), 150 mM NaCl (Kanto Chemical, Co., Inc., Tokyo, Japan), 1% Triton X-100 (MP Biomedicals LLC, Santa Ana, CA, USA), 5 µM ethylenediaminetetra acetic acid (Nacalai Tesque, Inc.), 1%sodium deoxycholate (Difco; BD Biosciences, San Jose, CA, USA), 0.1% sodium dodecyl sulfate, 1.2% aprotinin, 5 µM leupeptin, 4 µM antipain, 1 mM phenylmethylsulfonyl fluoride and 0.1 mM Na 3 VO 4 (all; Sigma Aldrich; Merck KGaA, Darmstadt, Germany) according to a previously described method (21). Samples were centrifuged at 16,000 x g for 20 min at 4˚C.…”