AKT and cytosolic phospholipase A2α form a positive loop in prostate cancer cells

Aberrant increase in protein kinase B (AKT) phosphorylation (pAKT), due to a gain-of-function mutation of phosphatidylinositol-3-kinase (P13K) or loss-of-function mutation or deletion of phosphatase and tensin homolog (PTEN), is a common alteration in prostate cancer and associated with poor prognosis. Cytosolic phospholipase A₂α (cPLA₂α) is a lipid modifying enzyme that catalyzes the hydrolysis of arachidonic acid from membrane phospholipid. The released arachidonic acid and its metabolites contribute to survival and proliferation of prostate cancer cells. In this mini-review, we summarize the relationship between pAKT and cPLA₂α in prostate cancer cells. There was a concordant increase in pAKT and cPLA₂α levels in prostate tissue of prostate epithelial-specific PTEN-knockout mice compared to PTEN-wild type mice. Restoration of PTEN expression or inhibition of P13K action decreased cPLA₂α protein levels. pAKT had no influence on cPLA₂α expression at mRNA levels but stabilized cPLA₂α at protein levels by protecting it from degradation. Conversely, an induction of cPLA₂α expression led to an increase in pAKT levels in PTEN-mutated or deleted prostate cancer cells while silencing of cPLA₂α expression or pharmacological blocking of cPLA₂α action decreased pAKT levels. The diminishment of pAKT by either genetic silencing or pharmacological blocking of cPLA₂α was mitigated by the addition of arachidonic acid. The stimulatory effect of arachidonic acid on pAKT levels was lessened by inhibiting the production of arachidonic acid metabolites. These studies have revealed a link between an oncogenic pathway and lipid metabolism and provided potential molecular targets for treating prostate cancer

Loss of PTEN stabilizes the lipid modifying enzyme cytosolic phospholipase A₂α via AKT in prostate cancer cells

Aberrant increase in pAKT, due to a gain-of-function mutation of PI3K or lossof-function mutation or deletion of PTEN, occurs in prostate cancer and is associated with poor patient prognosis. Cytosolic phospholipase A2a (cPLA2a) is a lipid modifying enzyme by catalyzing the hydrolysis of membrane arachidonic acid. Arachidonic acid and its metabolites contribute to survival and proliferation of prostate cancer cells. We examined whether AKT plays a role in promoting cPLA2a action in prostate cancer cells. We found a concordant increase in pAKT and cPLA2a levels in prostate tissue of prostate epithelial-specific PTEN-knockout but not PTEN-wide type mice. Restoration of PTEN expression or inhibition of PI3K action decreased cPLA2a expression in PTENmutated or deleted prostate cancer cells. An increase in AKT by Myr-AKT elevated cPLA2a protein levels, which could be diminished by inhibition of AKT phosphorylation without noticeable change in total AKT levels. pAKT levels had no influence on cPLA2a at mRNA levels but reduced cPLA2a protein degradation. Anti-AKT antibody coimmunoprecipitated cPLA2a and vice versa. Hence, AKT plays a role in enhancing cPLA2a protein stability in PTEN-null prostate cancer cells, revealing a link between oncogenic pathway and lipid metabolism

Food extracts consumed in Mediterranean countries and East Asia reduce protein concentrations of androgen receptor, phospho-protein kinase B, and phospho-cytosolic phospholipase A2α in human prostate cancer cells

Active surveillance is an emerging management option for the rising number of men with low-grade, clinically localized prostate cancer. However, 30-40% of men on active surveillance will progress to high-grade disease over 5 y. With the ultimate aim of developing a food-based chemoprevention strategy to retard cancer progression in these otherwise healthy men, we have developed a blend of food extracts commonly consumed in Mediterranean countries and East Asia. The effect of the food extracts known as Blueberry Punch (BBP) on prostate cancer cell growth and key signaling pathways were examined in vitro and in vivo. BBP reduced prostate cancer cell growth in a dose-dependent manner (0.08-2.5%) at 72 h in vitro due to the reduction in cell proliferation and viability. Prostate cancer cell xenograft-bearing mice, administered 10% BBP in drinking water for 2 wk, had a 25% reduction in tumor volume compared with the control (water only). In vitro, BBP reduced protein concentrations in 3 signaling pathways necessary for the proliferation and survival of prostate cancer cells, namely androgen receptor, phospho-protein kinase B/protein kinase B, and phospho-cytosolic phospholipase A2α. The downstream effectors of these pathways, including prostate-specific antigen and glycogen synthase kinase 3β, were also reduced. Thus, this palatable food supplement is a potential candidate for testing in clinical trials and may ultimately prove effective in retarding the progression of low-grade, early-stage prostate cancer in men managed by active surveillance

Decrease in expression or activity of cytosolic phospholipase A2α increases cyclooxygenase-1 action : a cross-talk between key enzymes in arachidonic acid pathway in prostate cancer cells

The eicosanoid pathway is activated in many types of cancers including prostate. Eicosanoids are synthesized from intracellular arachidonic acid (AA), which is released from membrane glycerophospholipids mainly by the action of cytosolic phospholipase A2α (cPLA2α). Thus, targeting cPLA2α has been proposed as a treatment option. The aim of this study was to determine the effect of cPLA2α inhibition on cyclooxygenase (COX) expression and PGE2 production. Inhibition of cPLA2α expression by siRNA or activity by Efipladib in prostate cancer cell lines (PC3 and LNCaP) led to an increase in COX-1 protein and PGE2 levels in a dose-dependent manner from 24 to 72 h. The COX-2 response was less evident. Efipladib treatment increased COX-1 promoter transcriptional activity without changing the rate of COX-1 protein degradation. Treatment with Efipladib also led to a decrease in most LOX products (HETEs) as measured by LC/MS/MS. Replenishing 5- and 12-HETEs abolished Efipladib-induced COX-1 and PGE2 levels. Decreasing 5- and 12-HETE production, as a result of treating cells with inhibitors MK886 and Baicalein, respectively, mimicked the effect of Efipladib on COX-1 and PGE2 levels. Hence, the mechanism underlying the cPLA2α inhibition-induced COX-1 is likely due to a decrease in LOX products, which may exert a negative feedback on COX-1 gene expression in prostate cancer cells. Considering that PGE2 is a potent promoter of cancer cell proliferation and survival, understanding the mechanism coupling cPLA2α with COX-1 is of potential clinical significance

Cytosolic phospholipase A2α sustains pAKT, pERK and AR levels in PTEN-null/mutated prostate cancer cells

Constitutive phosphorylation of protein kinase B (AKT) is a common feature of cancer caused by genetic alteration in the phosphatase and tensin homolog (PTEN) gene and is associated with poor prognosis. This study determined the role of cytosolic phospholipase A2? (cPLA2?) in AKT, extracellular signal-regulated kinase (ERK) and androgen receptor (AR) signaling in PTEN-null/mutated prostate cancer cells. Doxycycline (Dox)-induced expression of cPLA2? led to an increase in pAKT, pGSK3? and cyclin D1 levels in LNCaP cells that possess a PTEN frame-shift mutation. In contrast, silencing cPLA2? expression with siRNA decreased pAKT, pGSK3? and cyclin D1 levels in both PC-3 (PTEN deletion) and LNCaP cells. Silencing of cPLA2? decreased pERK and AR protein levels. The inhibitory effect of cPLA2? siRNA on pAKT and AR protein levels was reduced by the addition of arachidonic acid (AA), whereas the stimulatory effect of AA on pAKT, pERK and AR levels was decreased by an inhibitor of 5-hydroxyeicosatetraenoic acid production. Pharmacological blockade of cPLA2? with Efipladib reduced pAKT and AR levels with a concomitant inhibition of PC-3 and LNCaP cell proliferation. These results demonstrate an important role for cPLA2? in sustaining AKT, ERK and AR signaling in PTEN-null/mutated prostate cancer cells and provide a potential molecular target for treating prostate cancer

Targeting cytosolic phospholipase A2 α in colorectal cancer cells inhibits constitutively activated protein kinase B (AKT) and cell proliferation

A constitutive activation of protein kinase B (AKT) in a hyper-phosphorylated status at Ser473 is one of the hallmarks of anti-EGFR therapy-resistant colorectal cancer (CRC). The aim of this study was to examine the role of cytosolic phospholipase A2a (cPLA2a) on AKT phosphorylation at Ser473 and cell proliferation in CRC cells with mutation in phosphoinositide 3-kinase (PI3K). AKT phosphorylation at Ser473 was resistant to EGF stimulation in CRC cell lines of DLD-1 (PIK3CAE545K mutation) and HT-29 (PIK3CAP499T mutation). Over-expression of cPLA2a by stable transfection increased basal and EGF-stimulated AKT phosphorylation and proliferation in DLD- 1 cells. In contrast, silencing of cPLA2a with siRNA or inhibition with Efipladib decreased basal and EGF-stimulated AKT phosphorylation and proliferation in HT-29. Treating animals transplanted with DLD-1 with Efipladib (10 mg/kg, i.p. daily) over 14 days reduced xenograft growth by > 90% with a concomitant decrease in AKT phosphorylation. In human CRC tissue, cPLA2a expression and phosphorylation were increased in 63% (77/120) compared with adjacent normal mucosa determined by immunohistochemistry. We conclude that cPLA2a is required for sustaining AKT phosphorylation at Ser473 and cell proliferation in CRC cells with PI3K mutation, and may serve as a potential therapeutic target for treatment of CRC resistant to anti-EGFR therapy

The histone chaperone complex FACT promotes proliferative switch of G0 cancer cells

Cancer cell repopulation through cell cycle re‐entry by quiescent (G0) cell is thought to be an important mechanism behind treatment failure and cancer recurrence. Facilitates Chromatin Transcription (FACT) is involved in DNA repair, replication and transcription by eviction of histones or loosening their contact with DNA. While FACT expression is known to be high in a range of cancers, the biological significance of the aberrant increase is not clear. We found that in prostate and lung cancer cells FACT mRNA and protein levels were low at G0 compared to the proliferating state but replenished upon cell cycle re‐entry. Silencing of FACT with Dox‐inducible shRNA hindered cell cycle re‐entry by G0cancer cells, which could be rescued by ectopic expression of FACT. An increase in SKP2, c‐MYC and PIRH2 and a decrease in p27 protein levels seen upon cell cycle re‐entry were prevented or diminished when FACT was silenced. Further, using mVenus‐p27K− infected cancer cells to measure p27 degradation capacity, we confirm that inhibition of FACT at release from quiescence suppressed the p27 degradation capacity resulting in an increased mVenus‐p27K− signal. In conclusion, FACT plays an important role in promoting the transition from G0 to the proliferative state and can be a potential therapeutic target to prevent prostate and lung cancer from progression and recurrence

Food Extracts Consumed in Mediterranean Countries and East Asia Reduce Protein Concentrations of Androgen Receptor, Phospho-Protein Kinase B, and Phospho-Cytosolic Phospholipase A2α in Human Prostate Cancer Cells

Active surveillance is an emerging management option for the rising number of men with low-grade, clinically localized prostate cancer. However, 30-40% of men on active surveillance will progress to high-grade disease over 5 y. With the ultimate aim of developing a food-based chemoprevention strategy to retard cancer progression in these otherwise healthy men, we have developed a blend of food extracts commonly consumed in Mediterranean countries and East Asia. The effect of the food extracts known as Blueberry Punch (BBP) on prostate cancer cell growth and key signaling pathways were examined in vitro and in vivo. BBP reduced prostate cancer cell growth in a dose-dependent manner (0.08-2.5%) at 72 h in vitro due to the reduction in cell proliferation and viability. Prostate cancer cell xenograft-bearing mice, administered 10% BBP in drinking water for 2 wk, had a 25% reduction in tumor volume compared with the control (water only). In vitro, BBP reduced protein concentrations in 3 signaling pathways necessary for the proliferation and survival of prostate cancer cells, namely androgen receptor, phospho-protein kinase B/protein kinase B, and phospho-cytosolic phospholipase A2α. The downstream effectors of these pathways, including prostate-specific antigen and glycogen synthase kinase 3β, were also reduced. Thus, this palatable food supplement is a potential candidate for testing in clinical trials and may ultimately prove effective in retarding the progression of low-grade, early-stage prostate cancer in men managed by active surveillance