The Antiproliferative Effect of EPA in HL60 Cells is Mediated by Alterations in Calcium Homeostasis

Abstract

Studies show that n-3 polyunsaturated fatty acids (PUFA) inhibit proliferation and induce apoptosis in cancer cells. Recent reports indicate that this effect is due to activation of the unfolded protein response (UPR). However, what causes this activation has been unclear. We examined the effects of eicosapentaenoic acid (EPA) on the human leukemia cell line HL60 and the econazole (Ec) resistant HL60 clone E2R2. Ec depletes Ca(2+) from the ER and blocks Ca(2+) influx in mammalian cells, leading to activation of the UPR and apoptosis. EPA inhibited growth of HL60 cells strongly, while E2R2 cells were much less affected. Gene expression analysis of HL60 cells revealed extensive changes in transcripts related to the ER homeostasis, Ca(2+)-homeostasis and cell cycle/apoptosis. Protein levels of phosphorylated eIF2alpha, a selective translation inhibitor and UPR hallmark, activating transcription factor 4 (ATF4) and sequestosome-1 were moderately increased, whereas the cell cycle/progression protein cyclin D1 was decreased in HL60. In contrast, EPA concentrations that strongly inhibited and caused activation of the UPR in HL60 cells had no effect on the expression level of these UPR markers in E2R2 cells. Given that the only known difference between these cells is Ec-resistance, our results strongly suggest that the inhibitory effect of EPA on HL60 cells is initially meditated through alterations of the Ca(2+)-homeostasis followed by activation of the UPR.

The unfolded protein response in the therapeutic effect of hydroxy-DHA against Alzheimer’s disease

“…This effect was proposed to take place downstream perturbations in Ca 2? homeostasis and oxidative stress, unavoidably driving cancer cells towards apoptosis [63,64]. Interestingly, DHA-mediated UPR in such cancer cell lines was characterized by a time-and dose-dependent up-regulation of eIF2a phosphorylation and CHOP expression, similarly to that shown here (Fig.…”

Tetradecylthioacetic acid inhibits proliferation of human SW620 colon cancer cells - gene expression profiling implies endoplasmic reticulum stress

“…We have previously shown that DHA induces ER stress with increased eIF2α-P, ATF4 and CHOP in the same cell line [28,62]. We also found HL-60 leukemia cells to induce ER stress upon EPA treatment [63]. …”

“…ER stress-accompanied changes in the Ca 2+ metabolism may lead to a pro-apoptotic signal via the mitochondria [66]. We have previously shown that DHA and EPA affect Ca 2+ homeostasis in cancer cells [28,63]. Apoptosis has been observed in other cancer cells treated with TTA [13,22], and it has been proposed that this effect is mediated via mitochondrial alterations, such as decrease in mitochondrial membrane potential and release of Cyt C [13].…”

“…For detection of eIF2α-P and cyclin D1, cells were harvested as elaborated in [28], and cytosolic protein extracts were prepared immediately in lysis buffer as described in [63]. Nuclear protein extracts for detection of ATF4, CHOP, TRIB3 and C/EBPβ were obtained by using Nuclear Extract Kit (Active Motif, Rixensart, Belgium) according to the manufacturer's protocol.…”

Transcriptomic Profiling of MDA-MB-231 Cells Exposed to Boswellia Serrata and 3-O-Acetyl-Β-Boswellic Acid; ER/UPR Mediated Programmed Cell Death

“…Many natural products are being reported to impact the aforementioned, including a spiked rise in Grp78, CHOP with activated ER/UPR -PCD occurring through PERK, IRE1alpha and ATF6 pathways as in the case of cryptotanshinone (32) 2-(3,4-dihydroxyphenyl)ethanol (olive oil) (58) selenium (59) methylseleninic acid, sodium selenite (33) xanthohumol (hops), docosahexaenoic acid (34,35) isochaihulactone (Nan-Chai-Hu) (36) Shikonin (Lithospermum erythrorhizon) (37) chrysin (31) curcumin (40) silibinin (41) or whole herbs such as the Chinese herbal medicine Tu Bei Mu (39). A number of drugs also mediate similar effects, such as steroids, platins, taxol, alkylating agents, or cancer chemicals which on the one hand block the growth of diverse cancers, and on the other hand elevate ER/UPR -PCD, associated with up-regulation of GRP78, CHOP and three UPRassociated pathways, PERK, IRE1alpha, and ATF6 (42-44, 46, 60).…”