A p85 isoform switch enhances PI3K activation on endosomes by a MAP4- and PI3P-dependent mechanism

Phosphatidylinositol 3-kinase α (PI3Kα) is a heterodimer of p110α catalytic and p85 adaptor subunits that is activated by agonist-stimulated receptor tyrosine kinases. Although p85α recruits p110α to activated receptors on membranes, p85α loss, which occurs commonly in cancer, paradoxically promotes agonist-stimulated PI3K/Akt signaling. p110α localizes to microtubules via microtubule-associated protein 4 (MAP4), facilitating its interaction with activated receptor kinases on endosomes to initiate PI3K/Akt signaling. Here, we demonstrate that in response to agonist stimulation and p85α knockdown, the residual p110α, coupled predominantly to p85β, exhibits enhanced recruitment with receptor tyrosine kinases to endosomes. Moreover, the p110α C2 domain binds PI3-phosphate, and this interaction is also required to recruit p110α to endosomes and for PI3K/Akt signaling. Stable knockdown of p85α, which mimics the reduced p85α levels observed in cancer, enhances cell growth and tumorsphere formation, and these effects are abrogated by MAP4 or p85β knockdown, underscoring their role in the tumor-promoting activity of p85α loss.

p85α regulatory subunit isoform controls PI3-kinase and TRPC6 membrane translocation

Activation of phosphatidylinositol 3-kinase (PI3K) by lipid oxidation products, including lysophosphatidylcholine (lysoPC), increases the externalization of canonical transient receptor potential 6 (TRPC6) channels leading to a subsequent increase in intracellular calcium that contributes to cytoskeletal changes which inhibit endothelial cell (EC) migration in vitro and impair EC healing of arterial injuries in vivo. The PI3K p110α and p110δ catalytic subunit isoforms regulate lysoPC-induced TRPC6 externalization in vitro, but have many other functions. The goal of the current study is to identify the PI3K regulatory subunit isoform involved in TRPC6 externalization to potentially identify a more specific treatment regimen to improve EC migration and arterial healing, while minimizing off-target effects. Decreasing the p85α regulatory subunit isoform protein levels, but not the p85β and p55γ regulatory subunit isoforms, with small interfering RNA inhibits lysoPC-induced translocation of the PI3K catalytic subunit to the plasma membrane, dramatically decreased phosphatidylinositol (3,4,5)-trisphosphate (PIP3) production and TRPC6 externalization, and significantly improves EC migration in the presence of lysoPC. These results identify the important and specific role of p85α in controlling translocation of PI3K from the cytosol to the plasma membrane and PI3K-mediated TRPC externalization by oxidized lipids. Current PI3K inhibitors block the catalytic subunit, but our data suggest that the regulatory subunit is a novel therapeutic target to promote EC migration and healing after arterial injuries that occur with angioplasty.

PIK-24 Inhibits RSV-Induced Syncytium Formation via Direct Interaction with the p85α Subunit of PI3K

Phosphoinositide-3 kinase (PI3K) signaling regulates many cellular processes, including cell survival, differentiation, proliferation, cytoskeleton reorganization, and apoptosis. The actin cytoskeleton regulated by PI3K signaling plays an important role in plasma membrane rearrangement. Currently, it is known that respiratory syncytial virus (RSV) infection requires PI3K signaling. However, the regulatory pattern or corresponding molecular mechanism of PI3K signaling on cell-to-cell fusion during syncytium formation remains unclear. This study synthesized a novel PI3K inhibitor PIK-24 designed with PI3K as a target and used it as a molecular probe to investigate the involvement of PI3K signaling in syncytium formation during RSV infection. The results of the antiviral mechanism revealed that syncytium formation required PI3K signaling to activate RHO family GTPases Cdc42, to upregulate the inactive form of cofilin, and to increase the amount of F-actin in cells, thereby causing actin cytoskeleton reorganization and membrane fusion between adjacent cells. PIK-24 treatment significantly abolished the generation of these events by blocking the activation of PI3K signaling. Moreover, PIK-24 had an obvious binding activity with the p85α regulatory subunit of PI3K. The anti-RSV effect similar to PIK-24 was obtained after knockdown of p85α in vitro or knockout of p85α in vivo, suggesting that PIK-24 inhibited RSV infection by targeting PI3K p85α. Most importantly, PIK-24 exerted a potent anti-RSV activity, and its antiviral effect was stronger than that of the classic PI3K inhibitor LY294002, PI-103, and broad-spectrum antiviral drug ribavirin. Thus, PIK-24 has the potential to be developed into a novel anti-RSV agent targeting cellular PI3K signaling. IMPORTANCE PI3K protein has many functions and regulates various cellular processes. As an important regulatory subunit of PI3K, p85α can regulate the activity of PI3K signaling. Therefore, it serves as the key target for virus infection. Indeed, p85α-regulated PI3K signaling facilitates various intracellular plasma membrane rearrangement events by modulating the actin cytoskeleton, which may be critical for RSV-induced syncytium formation. In this study, we show that a novel PI3K inhibitor inhibits RSV-induced PI3K signaling activation and actin cytoskeleton reorganization by targeting the p85α protein, thereby inhibiting syncytium formation and exerting a potent antiviral effect. Respiratory syncytial virus (RSV) is one of the most common respiratory pathogens, causing enormous morbidity, mortality, and economic burden. Currently, no effective antiviral drugs or vaccines exist for RSV infection. This study contributes to understanding the molecular mechanism by which PI3K signaling regulates syncytium formation and provides a leading compound for anti-RSV infection drug development.

Cancer-associated mutations in the p85α N-terminal SH2 domain activate a spectrum of receptor tyrosine kinases

Phosphoinositide 3-kinase activation typically occurs following stimulation by upstream receptor tyrosine kinases (RTKs), which alleviate p110α inhibition by p85α. p85α and p110α driver mutations have been reported to activate p110α by disrupting the inhibitory interface between p85α and p110α. This study revealed that driver mutations in the p85α N-terminal SH2 domain can enhance p110α activity by inducing the activation of multiple RTKs. Furthermore, combination treatment with RTK and AKT inhibitors provides synergistic therapeutic efficacy. This previously uncharacterized oncogenic mechanism presents the exploitable vulnerability of a class of p85α mutant tumors.

The phosphoinositide 3-kinase regulatory subunit p85α is a key regulator of kinase signaling and is frequently mutated in cancers. In the present study, we showed that in addition to weakening the inhibitory interaction between p85α and p110α, a group of driver mutations in the p85α N-terminal SH2 domain activated EGFR, HER2, HER3, c-Met, and IGF-1R in a p110α-independent manner. Cancer cells expressing these mutations exhibited the activation of p110α and the AKT pathway. Interestingly, the activation of EGFR, HER2, and c-Met was attributed to the ability of driver mutations to inhibit HER3 ubiquitination and degradation. The resulting increase in HER3 protein levels promoted its heterodimerization with EGFR, HER2, and c-Met, as well as the allosteric activation of these dimerized partners; however, HER3 silencing abolished this transactivation. Accordingly, inhibitors of either AKT or the HER family reduced the oncogenicity of driver mutations. The combination of these inhibitors resulted in marked synergy. Taken together, our findings provide mechanistic insights and suggest therapeutic strategies targeting a class of recurrent p85α mutations.

Case Report: EBV Chronic Infection and Lymphoproliferation in Four APDS Patients: The Challenge of Proper Characterization, Therapy, and Follow-Up

Activated PI3K-kinase Delta Syndrome (APDS) is an autosomal-dominant primary immunodeficiency (PID) caused by the constitutive activation of the PI3Kδ kinase. The consequent hyperactivation of the PI3K-Akt-mTOR pathway leads to an impaired T- and B-cells differentiation and function, causing progressive lymphopenia, hypogammaglobulinemia and hyper IgM. Patients with APDS show recurrent sinopulmonary and chronic herpes virus infections, immune dysregulation manifestations, including cytopenia, arthritis, inflammatory enteropathy, and a predisposition to persistent non-neoplastic splenomegaly/lymphoproliferation and lymphoma. The recurrence of the lymphoproliferative disorder and the difficulties in the proper definition of malignancy on histological examination represents the main challenge in the clinical management of APDS patients, since a prompt and correct diagnosis is needed to avoid major complications. Targeted therapies with PI3Kδ-Akt-mTOR pathway pharmacologic inhibitors (i.e., Rapamycin, Theophylline, PI3K inhibitors) represent a good therapeutic strategy. They can also be used as bridge therapies when HSCT is required in order to control refractory symptoms. Indeed, treated patients showed a good tolerance, improved immunologic phenotype and reduced incidence/severity of immune dysregulation manifestations. Here, we describe our experience in the management of four patients, one male affected with APDS1 (P1) and the other three, a male and two females, with APDS2 (P2, P3, P4) presenting with chronic EBV replication, recurrent episodes of immune dysregulation manifestations and lymphomas. These cases highlighted the importance of a tailored and close follow-up, including serial endoscopic and lymph nodes biopsies control to detect a prompt and correct diagnosis and offer the best therapeutic strategy.

piR-001773 and piR-017184 promote prostate cancer progression by interacting with PCDH9

Prostate cancer is one of the most common malignancies and the major cause of cancer-related death in men. Increasing evidence has revealed that P-element-induced wimpy (piwi)-interacting RNAs (piRNAs) play an important role in tumor progression. Few studies have been explored the functional mechanism of piRNAs in prostate cancer progression. In the present study, we demonstrated that piR-001773 and piR-017184 were increased in prostate cancer tissues. Protocadherin 9 (PCDH9) was downregulated and acted as a tumor suppressor in prostate cancer cells. PCDH9 could bind to p85α, the regulatory subunit of PI3K. The downregulation of PCDH9 in PCa cells resulted in an increase in AKT phosphorylation and activity. PCDH9 was posttranscriptionally regulated by piR-001773 and piR-017184. The upregulation of piR-001773 and piR-017184 promoted tumor growth both in vitro and in vivo. In addition, the downregulation of piR-001773 and piR-017184 markedly inhibited tumor growth. In conclusion, these results indicated that piR-001773 and piR-017184 are oncogenic RNAs and thus might be therapeutic targets in prostate cancer.

Oleic Acid Protects Against Insulin Resistance by Regulating the Genes Related to the PI3K Signaling Pathway

BACKGROUND

The effects of different types of fatty acids on the gene expression of key players in the IRS1/PI3K signaling pathway have been poorly studied.

MATERIAL AND METHODS

We analyzed IRS1, p85α, and p110β mRNA expression and the fatty acid composition of phospholipids in visceral adipose tissue from patients with morbid obesity and from non-obese patients. Moreover, we analyzed the expression of those genes in visceral adipocytes incubated with oleic, linoleic, palmitic and dosahexaenoic acids.

RESULTS

We found a reduced IRS1 expression in patients with morbid obesity, independent of insulin resistance, and a reduced p110β expression in those with lower insulin resistance. A positive correlation was found between p85α and stearic acid, and between IRS1 and p110β with palmitic and dosahexaenoic acid. In contrast, a negative correlation was found between p85α and oleic acid, and between IRS1 and p110β with linoleic, arachidonic and adrenic acid. Incubation with palmitic acid decreased IRS1 expression. p85α was down-regulated after incubation with oleic and dosahexaenoic acid and up-regulated with palmitic acid. p110β expression was increased and decreased after incubation with oleic and palmitic acid, respectively. The ratio p85α/p110β was decreased by oleic and dosahexaenoic acid and increased by palmitic acid.

CONCLUSIONS

Our in vitro results suggest a detrimental role of palmitic acid on the expression of gene related to insulin signaling pathway, with oleic acid being the one with the higher and more beneficial effects. DHA had a slight beneficial effect. Fatty acid-induced regulation of genes related to the IRS1/PI3K pathway may be a novel mechanism by which fatty acids regulate insulin sensitivity in visceral adipocytes.

PI3K pathway defects leading to immunodeficiency and immune dysregulation

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is involved in a broad range of cellular processes, including growth, metabolism, differentiation, proliferation, motility, and survival. The PI3Kδ enzyme complex is primarily present in the immune system and comprises a catalytic (p110δ) and regulatory (p85α) subunit. Dynamic regulation of PI3Kδ activity is required to ensure normal function and differentiation of immune cells. In the last decade, discovery of germline mutations in genes involved in the PI3Kδ pathway (PIK3CD, PIK3R1, or phosphatase and tensin homolog [PTEN]) proved that both overactivation and underactivation (gain of function and loss of function, respectively) of PI3Kδ lead to impaired and dysregulated immunity. Although a small group of patients reported to underactivate PI3Kδ show predominantly humoral defects and autoimmune features, more than 200 patients have been described with overactivation of PI3Kδ, presenting with a much more complex phenotype of combined immunodeficiency and immune dysregulation. The clinical and immunologic characterization, as well as current pathophysiologic understanding and specific therapies for PI3K pathway defects leading to immunodeficiency and immune dysregulation, are reviewed here.

Impairment of Membrane Lipid Homeostasis by Bichalcone Analog TSWU-BR4 Attenuates Function of GRP78 in Regulation of the Oxidative Balance and Invasion of Cancer Cells

The specialized cholesterol/sphingolipid-rich membrane domains termed lipid rafts are highly dynamic in the cancer cells, which rapidly assemble effector molecules to form a sorting platform essential for oncogenic signaling transduction in response to extra- or intracellular stimuli. Density-based membrane flotation, subcellular fractionation, cell surface biotinylation, and co-immunoprecipitation analyses of bichalcone analog ((E)-1-(4-Hydroxy-3-((4-(4-((E)-3-(pyridin-3-yl)acryloyl)phenyl)piperazin-1-yl)methyl)phenyl)-3-(pyridin-3-yl)prop-2-en-1-one (TSWU-BR4)-treated cancer cells showed dissociation between GRP78 and p85α conferring the recruitment of PTEN to lipid raft membranes associated with p85α. Ectopic expression of GRP78 could overcome induction of lipid raft membrane-associated p85α–unphosphorylated PTEN complex formation and suppression of GRP78−PI3K−Akt−GTP-Rac1-mediated and GRP78-regulated PERK−Nrf2 antioxidant pathway and cancer cell invasion by TSWU-BR4. Using specific inducer, inhibitor, or short hairpin RNA for ASM demonstrated that induction of the lipid raft membrane localization and activation of ASM by TSWU-BR4 is responsible for perturbing homeostasis of cholesterol and ceramide levels in the lipid raft and ER membranes, leading to alteration of GRP78 membrane trafficking and subsequently inducing p85α–unphosphorylated PTEN complex formation, causing disruption of GRP78−PI3K−Akt−GTP-Rac1-mediated signal and ER membrane-associated GRP78-regulated oxidative stress balance, thus inhibiting cancer cell invasion. The involvement of the enrichment of ceramide to lipid raft membranes in inhibition of NF-κB-mediated MMP-2 expression was confirmed through attenuation of NF-κB activation using C2-ceramide, NF-κB specific inhibitors, ectopic expression of NF-κB p65, MMP-2 promoter-driven luciferase, and NF-κB-dependent reporter genes. In conclusion, localization of ASM in the lipid raft membranes by TSWU-BR4 is a key event for initiating formation of ceramide-enriched lipid raft membrane platforms, which causes delocalization of GRP78 from the lipid raft and ER membranes to the cytosol and formation of p85α–unphosphorylated PTEN complexes to attenuate the GRP78-regulated oxidative stress balance and GRP78−p85α−Akt−GTP-Rac1−NF-κB−MMP-2-mediated cancer cell invasion.

Specific knockout of p85α in brown adipose tissue induces resistance to high-fat diet-induced obesity and its metabolic complications in male mice

Objective

An increase in mass and/or brown adipose tissue (BAT) functionality leads to an increase in energy expenditure, which may be beneficial for the prevention and treatment of obesity. Moreover, distinct class I PI3K isoforms can participate in metabolic control as well as in systemic dysfunctions associated with obesity. In this regard, we analyzed in vivo whether the lack of p85α in BAT (BATp85αKO) could modulate the activity and insulin signaling of this tissue, thereby improving diet-induced obesity and its associated metabolic complications.

Methods

We generated BATp85αKO mice using Cre-LoxP technology, specifically deleting p85α in a conditional manner. To characterize this new mouse model, we used mice of 6 and 12 months of age. In addition, BATp85αKO mice were submitted to a high-fat diet (HFD) to challenge BAT functionality.

Results

Our results suggest that the loss of p85α in BAT improves its thermogenic functionality, high-fat diet–induced adiposity and body weight, insulin resistance, and liver steatosis. The potential mechanisms involved in the improvement of obesity include (1) increased insulin signaling and lower activation of JNK in BAT, (2) enhanced insulin receptor isoform B (IRB) expression and association with IRS-1 in BAT, (3) lower production of proinflammatory cytokines by the adipose organ, (4) increased iWAT browning, and (5) improved liver steatosis.

Conclusions

Our results provide new mechanisms involved in the resistance to obesity development, supporting the hypothesis that the gain of BAT activity induced by the lack of p85α has a direct impact on the prevention of diet-induced obesity and its associated metabolic complications.

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The lack of p85α in brown adipose tissue confers obesity resistance.

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BATp85αKO mice show improved thermogenic function, fatty liver and insulin resistance.

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High IRB levels in BAT and iWAT browning might explain the improvement of obesity.

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Increase in BAT functionality has a direct impact on the prevention of obesity.

ATM Regulated PTEN Degradation Is XIAP E3 Ubiquitin Ligase Mediated in p85α Deficient Cancer Cells and Influence Platinum Sensitivity

Ataxia-telegiectasia mutated (ATM), phosphatase and tensin homolog (PTEN), and p85α are key tumour suppressors. Whether ATM regulates PTEN expression and influence platinum sensitivity is unknown. We generated ATM knockdowns (KD) and CRISPR knock outs (KO) in glioblastoma (LN18, LN229) and ovarian cancer cells (OVCAR3, OVCAR4). Doxycycline inducible PTEN expression was generated in LN18 and LN229 cells. Transient KD of p85α, CK2, and XIAP was accomplished using siRNAs. Stable p85α knock-in was isolated in LN18 cells. Molecular biology assays included proteasome activity assays, PCR, flow cytometry analysis (cell cycle, double strand break accumulation, apoptosis), immunofluorescence, co-immunoprecipitation, clonogenic, invasion, migration, and 3D neurosphere assays. The clinicopathological significance of ATM, PTEN, p85α, and XIAP (X-linked inhibitor of apoptosis protein) was evaluated in 525 human ovarian cancers using immunohistochemistry. ATM regulated PTEN is p85α dependant. ATM also controls CK2α level which in turn phosphorylates and stabilizes PTEN. In addition, p85α physically interacts with CK2α and protects CK2α from ATM regulated degradation. ATM deficiency resulted in accumulation of XIAP/p-XIAP levels which ubiquitinated PTEN and CK2α thereby directing them to degradation. ATM depletion in the context of p85α deficiency impaired cancer cell migration and invasion reduced 3D-neurosphere formation and increased toxicity to cisplatin chemotherapy. Increased sensitivity to platinum was associated with DNA double strand breaks accumulation, cell cycle arrest, and induction of autophagy. In ovarian cancer patients, ATM, PTEN, p85α, and XIAP protein levels predicted better progression free survival after platinum therapy. We unravel a previously unknown function of ATM in the regulation of PTEN throμgh XIAP mediated proteasome degradation.

Downregulation of miR-144 by triptolide enhanced p85α-PTEN complex formation causing S phase arrest of human nasopharyngeal carcinoma cells

Selective pharmacologic targeting of cell cycle regulators is a potent anti-cancer therapeutic strategy. Here, we show that caspase-3-mediated p21 cleavage involves p53 independent of triptolide (TPL)-induced S phase arrest in human type 1 nasopharyngeal carcinoma (NPC) cells. Coimmunoprecipitation studies demonstrated that TPL causes S phase cell cycle arrest by suppressing the formation of cyclin A-phosphor (p)-cyclin-dependent kinas 2 (CDK2) (Thr 39) complexes. Ectopic expression of constitutively active protein kinase B1 (Akt1) blocks the induction of S phase arrest and the suppression of cyclin A expression and CDK2 Thr 39 phosphorylation by TPL. Expression of the phosphomimetic mutant CDK2 (T39E) rescues the cells from TPL-induced S phase arrest, whereas phosphorylation-deficient CDK2 (T39A) expression regulates cell growth with significant S phase arrest and enhances TPL-triggered S phase arrest. Treatment with TPL induces an increase in the formation of complexes between unphosphorylated phosphatase and tensin homolog deleted from chromosome 10 (PTEN) and p85α in the plasma membrane. Decreased microRNA (miR)-144 expression and increased PTEN expression after TPL treatment were demonstrated, and TPL-enhanced p85α-PTEN complexes and inhibitory effects on Akt (Ser 473) phosphorylation and S phase arrest were suppressed by ectopic PTEN short hairpin RNA or miR-144 expression. Knockdown of endogenous miR-144 by miR-144 Trap upregulated PTEN expression and accordingly enhanced p85α-PTEN complex formation and S phase arrest. Collectively, the effect of TPL on S phase arrest in human NPC cells is likely to enhance the p85α-PTEN interaction in the plasma membrane by suppressing miR-144 expression, resulting in the attenuation of cyclin A-p-CDK2 (Thr 39) complex formation via Akt inactivation.

Citrate-Induced p85α⁻PTEN Complex Formation Causes G2/M Phase Arrest in Human Pharyngeal Squamous Carcinoma Cell Lines

Citrate is a key intermediate of the tricarboxylic acid cycle and acts as an allosteric signal to regulate the production of cellular ATP. An elevated cytosolic citrate concentration inhibits growth in several types of human cancer cells; however, the underlying mechanism by which citrate induces the growth arrest of cancer cells remains unclear. The results of this study showed that treatment of human pharyngeal squamous carcinoma (PSC) cells with a growth-suppressive concentration of citrate caused cell cycle arrest at the G₂/M phase. A coimmunoprecipitation study demonstrated that citrate-induced cell cycle arrest in the G₂/M phase was associated with stabilizing the formation of cyclin B1-phospho (p)-cyclin-dependent kinase 1 (CDK1) (Thr 161) complexes. The citrate-induced increased levels of cyclin B1 and G₂/M phase arrest were suppressed by the caspase-3 inhibitor Ac-DEVD-CMK and caspase-3 cleavage of mutant p21 (D112N). Ectopic expression of the constitutively active form of protein kinase B (Akt1) could overcome the induction of p21 cleavage, cyclin B1-p-CDK1 (Thr 161) complexes, and G₂/M phase arrest by citrate. p85α-phosphatase and tensin homolog deleted from chromosome 10 (PTEN) complex-mediated inactivation of Akt was required for citrate-induced G₂/M phase cell cycle arrest because PTEN short hairpin RNA or a PTEN inhibitor (SF1670) blocked the suppression of Akt Ser 473 phosphorylation and the induction of cyclin B1-p-CDK1 (Thr 161) complexes and G₂/M phase arrest by citrate. In conclusion, citrate induces G₂/M phase arrest in PSC cells by inducing the formation of p85α-PTEN complexes to attenuate Akt-mediated signaling, thereby causing the formation of cyclin B1-p-CDK1 (Thr 161) complexes.

Insight into the PTEN - p85α interaction and lipid binding properties of the p85α BH domain

The phosphatidylinositol 3-kinase (PI3K) pathway plays a key role in regulating cell growth and cell survival and is frequently deregulated in cancer cells. p85α regulates the p110α lipid kinase, and also stabilizes and stimulates PTEN, the lipid phosphatase that downregulates this pathway. In this report, we determined that the p85α BH domain binds several phosphorylated phosphoinositide lipids, an interaction that could help localize p85α to membranes rich in these lipids. We also identified key residues responsible for mediating PTEN – p85α complex formation. Based on these experimental results, a docking model for the PTEN – p85α BH domain complex was developed that is consistent with the known binding interactions for both PTEN and p85α. This model involves extensive side-chain and peptide backbone contacts between both the PASE and C2 domains of PTEN with the p85α BH domains. The p85α BH domain residues shown to be important for PTEN binding were p85α residues E212, Q221, K225, R228 and H234. We also verified experimentally the importance of PTEN-E91 in mediating the interaction with the p85α BH domain. These results shed new light on the mechanism of PTEN regulation by p85α.

MicroRNA-29 enhances autophagy and cleanses exogenous mutant αB-crystallin in retinal pigment epithelial cells

Retinal pigment epithelial cells (RPEs), a pigmented cell layer in the outer retina, are constantly exposed to photo-oxidative stress. Autophagy relieves the stress by removing oxidative protein adducts, protein aggregates, and damaged mitochondria. We previously found that miR-29 is downregulated in choroid/RPE tissue in a model of exudative age-related macular degeneration (AMD), suggesting that miR-29 deficiency may contribute to autophagy inhibition and AMD progression. Here we wanted to test whether overexpression of miR-29 in RPEs could enhance autophagy, thereby facilitating removal of drusen components. Indeed, overexpression of miR-29 in the RPEs increased autophagy, assessed by decreased protein levels of p62, increased lipid form of microtubule-associated protein light chain (LC3-II), and elevated autophagy flux. Furthermore, overexpression of miR-29 mitigated the formation of mutant αB-crystallin (R120G) protein aggregates. In probing the mechanism, we demonstrated that miR-29 post-transcriptionally repressed LAMPTOR1/p18 via targeting its 3'-UTRs of messenger RNA. MiR-29 overexpression and knockdown of LAMPTOR1/p18 led to limited mTORC1 recruitment to lysosomes and inhibition of mTORC1 activity. Altogether, miR-29 enhances autophagy which aids in removal of protein aggregates. These findings reveal a novel role of miR-29, which has the potential of being a therapeutic strategy for rescuing RPE degeneration in ocular disorders.

Role of p85α in neutrophil extra- and intracellular reactive oxygen species generation

Drug resistance is a growing problem that necessitates new strategies to combat pathogens. Neutrophil phagocytosis and production of intracellular ROS, in particular, has been shown to cooperate with antibiotics in the killing of microbes. This study tested the hypothesis that p85α, the regulatory subunit of PI3K, regulates production of intracellular ROS. Genetic knockout of p85α in mice caused decreased expression of catalytic subunits p110α, p110β, and p110δ, but did not change expression levels of the NADPH oxidase complex subunits p67^phox, p47^phox, and p40^phox. When p85α, p55α, and p50α (all encoded by Pik3r1) were deleted, there was an increase in intracellular ROS with no change in phagocytosis in response to both Fcγ receptor and complement receptor stimulation. Furthermore, the increased intracellular ROS correlated with significantly improved neutrophil killing of both methicillin-susceptible and methicillin-resistant S. aureus. Our findings suggest inhibition of p85α as novel approach to improving the clearance of resistant pathogens.

Anti-inflammatory effects of curcumin are associated with down regulating microRNA-155 in LPS-treated macrophages and mice

CONTEXT

The natural polyphenolic compound curcumin has been proved to modulate innate immune responses and possess anti-inflammatory properties. Nevertheless, the mechanism remains poorly understood, particularly regarding curcumin-regulated miRNAs under inflammatory response.

OBJECTIVE

This study investigates the role of miRNA-155 in the effects of curcumin on inflammatory response in cell and a mouse model.

MATERIALS AND METHODS

The anti-inflammatory activity of curcumin (5, 10 and 15 μM, 2 h) in lipopolysaccharide (LPS, 200 ng/mL)-induced cells were measured by quantitative PCR. The animals were treated orally by 20 mg/kg curcumin for 3 days before an LPS intraperitoneal injection (10 mg/kg, 16 h). MicroRNA (miRNA) expression and the underlying molecular mechanisms were assessed using transfection technique and western blotting.

RESULTS AND DISCUSSION

Curcumin efficiently inhibited LPS-induced cytokines (TNF-α, IL-6) and microRNA-155 (miR-155) expression (p < 0.05) without affecting the normally growth of Raw264.7 and THP-1 cells (IC₅₀ 21.8 and 22.3 μM at 48 h, respectively). Moreover, the levels of cytokines were suppressed by curcumin in miR-155 mimics transfected cells (p < 0.05). A blockade of PI3K/AKT signalling pathways resulted in a decreased level of miR-155 (p < 0.05). Curcumin effectively protected mice from sepsis as evidenced by decreasing histological damage, reducing AST (352.0 vs 279.3 U/L), BUN (14.8 vs 10.8 mmol/L) levels and the proportion of macrophages in spleen (31.1% vs 13.5%). MicroRNA-155 level and cytokines were also reduced in curcumin-treated mice (p < 0.05).

CONCLUSIONS

Curcumin's ability to suppress LPS-induced inflammatory response may be due to the inhibition of miR-155.

Insulin resistance and diabetes caused by genetic or diet-induced KBTBD2 deficiency in mice

We describe a metabolic disorder characterized by lipodystrophy, hepatic steatosis, insulin resistance, severe diabetes, and growth retardation observed in mice carrying N-ethyl-N-nitrosourea (ENU)-induced mutations. The disorder was ascribed to a mutation of kelch repeat and BTB (POZ) domain containing 2 (Kbtbd2) and was mimicked by a CRISPR/Cas9-targeted null allele of the same gene. Kbtbd2 encodes a BTB-Kelch family substrate recognition subunit of the Cullin-3-based E3 ubiquitin ligase. KBTBD2 targeted p85α, the regulatory subunit of the phosphoinositol-3-kinase (PI3K) heterodimer, causing p85α ubiquitination and proteasome-mediated degradation. In the absence of KBTBD2, p85α accumulated to 30-fold greater levels than in wild-type adipocytes, and excessive p110-free p85α blocked the binding of p85α-p110 heterodimers to IRS1, interrupting the insulin signal. Both transplantation of wild-type adipose tissue and homozygous germ line inactivation of the p85α-encoding gene Pik3r1 rescued diabetes and hepatic steatosis phenotypes of Kbtbd2^-/- mice. Kbtbd2 was down-regulated in diet-induced obese insulin-resistant mice in a leptin-dependent manner. KBTBD2 is an essential regulator of the insulin-signaling pathway, modulating insulin sensitivity by limiting p85α abundance.

p85α promotes nucleolin transcription and subsequently enhances EGFR mRNA stability and EGF-induced malignant cellular transformation

p85α is a regulatory subunit of phosphatidylinositol 3-kinase (PI3K) that is a key lipid enzyme for generating phosphatidylinositol 3, 4, 5-trisphosphate, and subsequently activates signaling that ultimately regulates cell cycle progression, cell growth, cytoskeletal changes, and cell migration. In addition to form a complex with the p110 catalytic subunit, p85α also exists as a monomeric form due to that there is a greater abundance of p85α than p110 in many cell types. Our previous studies have demonstrated that monomeric p85α exerts a pro-apoptotic role in UV response through induction of TNF-α gene expression in PI3K-independent manner. In current studies, we identified a novel biological function of p85α as a positive regulator of epidermal growth factor receptor (EGFR) expression and cell malignant transformation via nucleolin-dependent mechanism. Our results showed that p85α was crucial for EGFR and nucleolin expression and subsequently resulted in an increase of malignant cellular transformation by using both specific knockdown and deletion of p85α in its normal expressed cells. Mechanistic studies revealed that p85α upregulated EGFR protein expression mainly through stabilizing its mRNA, whereas nucleolin (NCL) was able to bind to egfr mRNA and increase its mRNA stability. Consistently, overexpression of NCL in p85α-/- cells restored EGFR mRNA stabilization, protein expression and cell malignant transformation. Moreover, we discovered that p85α upregulated NCL gene transcription via enhancing C-Jun activation. Collectively, our studies demonstrate a novel function of p85α as a positive regulator of EGFR mRNA stability and cell malignant transformation, providing a significant insight into the understanding of biomedical nature of p85α protein in mammalian cells and further supporting that p85α might be a potential target for cancer prevention and therapy.

Suppression of phospho-p85α-GTP-Rac1 lipid raft interaction by bichalcone analog attenuates cancer cell invasion

The p85α subunit of phosphatidylinositol 3-kinase (PI3K) acts as a key regulator of cell proliferation and motility, which mediates signals that confer chemoresistance to many human cancer cells. Using small interfering RNAs against matrix metalloproteinase-2 (MMP-2) and the MMP-2 promoter-driven luciferase assay, we showed that the new synthetic bichalcone analog TSWU-CD4 inhibits the invasion of human cancer cells by down-regulating MMP-2 expression. Treatment with TSWU-CD4 inhibited MMP-2 expression and cell invasion, which were restored by ectopic wild type (wt) p85α or a constitutively active form of MAPK kinase 3 (CA MKK3), CA MKK6, or CA p38α mitogen-activated protein kinase (MAPK). The attenuated formation of lipid raft-associated phospho (p)-p85α-GTP-Rac1 complexes, protein kinase B (Akt) Ser 473 phosphorylation, and cell invasion by TSWU-CD4 was reversed by overexpression of wt p85α or the p85α Brc-homology (BH) domain. The ectopic expression of CA Rac1^L61 (but not wt Rac1) could overcome the suppression of Ser 473 phosphorylation, lipid raft association of Akt, the interaction between GTP-bound Rac1 and p85α in lipid rafts, and cell invasion by TSWU-CD4. The involvement of Akt activity in the functions of NF-κB-mediated MMP-2 was further confirmed through the attenuation of Akt phosphorylation signaling using the Akt-specific inhibitor MK-2206 and ectopic expression of NF-κB p65. Collectively, the inhibitory effect of TSWU-CD4 on cancer cell invasion was likely to suppress the p-p85α-GTP-Rac1 interaction in lipid rafts by targeting the p85α BH domain, which resulted in the suppression of MMP-2 expression via the PI3K-Akt-mediated ERK-MKK3/MKK6-p38 MAPK-NF-κB signaling pathway. © 2016 Wiley Periodicals, Inc.

CHM-1 Suppresses Formation of Cell Surface-associated GRP78-p85α Complexes, Inhibiting PI3K-AKT Signaling and Inducing Apoptosis of Human Nasopharyngeal Carcinoma Cells

The endoplasmic reticulum chaperone glucose-regulated protein 78 (GRP78) is selectively expressed on the surface of cancer cells, and contributes to the survival of cancer cells by forming complexes with p85α and promoting phosphatidylinositol 3-kinase-protein kinase B (PI3K-AKT) signaling. Hereιin we report that 2'-fluoro-6,7-methylenedioxy-2-phenyl-4-quinolone (CHM-1) induces apoptosis of human nasopharyngeal carcinoma (NPC) cells, as characterized by morphological changes, DNA fragmentation, caspase-3 activation, and cleavage of poly (ADP-ribose) polymerase. Using cell surface biotinylation, flow cytometric analysis, co-immunoprecipitation, and ectopic expression of GRP78, we demonstrated that the attenuation of the cell surface localization and complex formation with p85α of GRP78 by CHM-1 was involved in the inhibition of PI3K-AKT signaling and the induction of apoptosis. CHM-1 treatment induced phosphorylation on Thr 69 of B cell lymphoma 2 and inhibited phosphorylation of Ser 136 on Bcl-2-associated death promoter, that were reversed by overexpression of GRP78. We further observed that loss of mitochondrial membrane potential and increase in reactive oxygen species content, release of mitochondrial cytochrome c, caspase-9 activation, and apoptotic cell death induced by CHM-1, were suppressed by treatment with cyclosporine A, and by the overexpression of constitutively active AKT1 or GRP78. These results indicate that CHM-1 induces NPC cell apoptosis by suppressing the formation of the cell surface-associated GRP78-PI3K-AKT signaling complex, likely through inhibition of the formation of cell surface-associated GRP78-p85α complexes.

The PI3K regulatory subunit gene PIK3R1 is under direct control of androgens and repressed in prostate cancer cells

Androgen receptor (AR) signalling and the PI3K pathway mediate survival signals in prostate cancer, and have been shown to regulate each other by reciprocal negative feedback, such that inhibition of one activates the other. Understanding the reciprocal regulation of these pathways is important for disease management as tumour cells can adapt and survive when either single pathway is inhibited pharmacologically. We recently carried out genome-wide exon-specific profiling of prostate cancer cells to identify novel androgen-regulated transcriptional events. Here we interrogated this dataset for novel androgen-regulated genes associated with the PI3K pathway. We find that the PI3K regulatory subunits PIK3R1 (p85α) and PIK3R3 (p55γ) are direct targets of the AR which are rapidly repressed by androgens in LNCaP cells. Further characterisation revealed that the PIK3CA p110α catalytic subunit is also indirectly regulated by androgens at the protein level. We show that PIK3R1 mRNA is significantly under-expressed in prostate cancer (PCa) tissue, and provide data to suggest a context-dependent regulatory mechanism whereby repression of the p85α protein by the AR results in destabilisation of the PI3K p110α catalytic subunit and downstream PI3K pathway inhibition that functionally affects the properties of prostate cancer cells.

AICAR enhances insulin signaling via downregulation of miR-29

As an activator of AMPK, the effect of AICAR on insulin signaling has not been investigated extensively. PI3K-Akt is a critical node involved in the insulin signaling pathway. We observed that concomitant with the activation of AMPK by AICAR, the protein level of PI3K p85α and the insulin-induced phosphorylation of Akt were enhanced in mouse primary hepatocytes. Previously, we identified a group of AMPK-regulated miRNAs in hepatocytes. It is not clear whether miRNAs are related to the regulation of insulin signaling by AMPK. Here, we confirmed the negative regulation of miR-29 family members by AICAR treatment in mouse primary hepatocytes. Our results indicated that p85α is a direct target of miR-29 and is negatively regulated by miR-29b in hepatocytes. In agreement with the findings in vitro, we found that the expression of miR-29 and the protein levels of p85α were inversely correlated in the liver of fasted mice. Overexpression of miR-29b reduced the insulin-induced phosphorylation of Akt in hepatocytes, suggesting that miR-29 could serve as a negative regulator of insulin signaling. Furthermore, we found that overexpression of miR-29 could attenuate the effect of AICAR on p85α expression. Taken together, our results indicated that activation of AMPK may enhance insulin signaling via downregulation of miR-29.

p85α is a microRNA target and affects chemosensitivity in pancreatic cancer

BACKGROUND

We previously identified a correlation between increased expression of the phosphoinositide 3-kinase (PI3K) regulatory subunit p85α and improved survival in human pancreatic ductal adenocarcinoma (PDAC). The purpose of this study was to investigate the impact of changes in p85α expression on response to chemotherapy and the regulation of p85α by microRNA-21 (miR-21).

MATERIALS AND METHODS

PDAC tumor cells overexpressing p85α were generated by viral transduction, and the effect of p85α overexpression on sensitivity to gemcitabine was tested by MTT assay. Primary human PDAC tumors were stained for p85α and miR-21 via immunohistochemistry and in situ hybridization, respectively. Additionally, PDAC cells were treated with miR-21 mimic, and changes in p85α and phospho-AKT were assessed by Western blot. Finally, a luciferase reporter assay system was used to test direct regulation of p85α by miR-21.

RESULTS

Higher p85α expression resulted in increased sensitivity to gemcitabine (P < 0.01), which correlated with decreased PI3K-AKT activation. Human tumors demonstrated an inverse correlation between miR-21 and p85α expression levels (r = -0.353, P < 0.001). In vitro, overexpression of miR-21 resulted in decreased levels of p85α and increased phosphorylation of AKT. Luciferase reporter assays confirmed the direct regulation of p85α by miR-21 (P < 0.01).

CONCLUSIONS

Our results demonstrate that p85α expression is a determinant of chemosensitivity in PDAC. Additionally, we provide novel evidence that miR-21 can influence PI3K-AKT signaling via its direct regulation of p85α. These data provide insight into potential mechanisms for the known relationship between increased p85α expression and improved survival in PDAC.

MicroRNA-486-5p, which is downregulated in hepatocellular carcinoma, suppresses tumor growth by targeting PIK3R1

Deregulated microRNAs and their roles in carcinogenesis and cancer progression have attracted much attention. In previous studies conducted in our laboratory, the Illumina Solexa massively parallel signature sequencing of miRNomes in nontumor and hepatocellular carcinoma (HCC) tissues revealed that miR-486-5p was significantly downregulated in HCC, but its role in HCC development remains unknown. In this study, miR-486-5p levels in HCC tissues and matched control tissues, and in seven HCC cell lines (QGY-7701, QGY-7703, QGY-7404, SMMC-7721, Huh7, HepG2, and PCL/PRF/5) and human normal liver cells (HL-7702), were tested by real-time quantitative RT-PCR. We found that the level of miR-486-5p was significantly decreased in HCC tissue and in all seven HCC cell lines. Overexpression of miR-486-5p markedly suppressed HCC cell proliferation, migration and invasion in vitro, and inhibited HCC growth in vivo. Mechanistically, miR-486-5p was confirmed to directly target PIK3R1 expression, thereby suppressing phosphatidylinositol 3-kinase-AKT pathway activation, by dual luciferase reporter assay and real-time quantitative RT-PCR and western blot analysis. In addition, PIK3R1 knockdown mimicked the effects of miR-486-5p overexpression by inhibiting HCC growth, migration, and invasion. Furthermore, correlation analysis, Kaplan-Meier estimates and Cox proportional hazard models showed an inverse correlation between miR-486-5p and PIK3R1, as well as a shorter time to recurrence after HCC resection, in patients with lower miR-486-5p expression. Hence, we conclude that miR-486-5p, which is frequently downregulated in HCC, inhibits HCC progression by targeting PIK3R1 and phosphatidylinositol 3-kinase-AKT activation.

A novel caveolin-1/p85α/Rab5/Tiam1/Rac1 signaling axis in tumor cell migration and invasion

The small GTPase Rab5 has been frequently studied in the context of intracellular trafficking, but evidence obtained more recently has implicated Rab5 as a critical regulator of cell adhesion, migration and invasion in both normal and tumor cells. These recent findings showing that Rab5 promotes Rac1 activation and focal adhesion dynamics have highlighted the question as to what the upstream regulators of Rab5 activity might be and how these are connected to cell migration. The efforts to shed light on this issue identified in metastatic cancer cells a novel Caveolin‑1/p85α/Rab5/Tiam1/Rac1 signaling axis relevant to cancer cell migration and invasion. In this addendum, we highlight aspects concerning Rab5 regulation in this context.

Rab5 is required in metastatic cancer cells for Caveolin-1-enhanced Rac1 activation, migration and invasion

Rab5 is a small GTPase that regulates early endosome trafficking and other cellular processes, including cell adhesion and migration. Specifically, Rab5 promotes Rac1 activation and cancer cell migration, but little is known about the upstream regulators of Rab5. We have previously shown that the scaffolding protein Caveolin-1 (CAV1) promotes Rac1 activation and migration of cancer cells. Here, we hypothesized that CAV1 stimulates Rab5 activation, leading to increased Rac1 activity and cell migration. Expression of CAV1 in B16-F10 mouse melanoma and HT-29(US) human colon adenocarcinoma cells increased the GTP loading of Rab5, whereas shRNA-mediated targeting of endogenous CAV1 in MDA-MB-231 breast cancer cells decreased Rab5-GTP levels. Accordingly, shRNA-mediated downregulation of Rab5 decreased CAV1-mediated Rac1 activation, cell migration and invasion in B16-F10 and HT-29(US) cells. Expression of CAV1 was accompanied by increased recruitment of Tiam1, a Rac1 guanine nucleotide exchange factor (GEF), to Rab5-positive early endosomes. Using the inhibitor NSC23766, Tiam1 was shown to be required for Rac1 activation and cell migration induced by CAV1 and Rab5. Mechanistically, we provide evidence implicating p85α (also known as PIK3R1), a Rab5 GTPase-activating protein (GAP), in CAV1-dependent effects, by showing that CAV1 recruits p85α, precluding p85α-mediated Rab5 inactivation and increasing cell migration. In summary, these studies identify a novel CAV1-Rab5-Rac1 signaling axis, whereby CAV1 prevents Rab5 inactivation, leading to increased Rac1 activity and enhanced tumor cell migration and invasion.

p85α mediates NFAT3-dependent VEGF induction in the cellular UVB response

Exposure to solar ultraviolet B (UVB) radiation is known to induce several pathological reactions in the skin. In these processes, upregulation of VEGF expression has been demonstrated to be important in angiogenesis-associated photodamage and even skin cancers. However, the signaling events that are responsible for VEGF induction under UVB exposure have not been fully defined. Here, we demonstrate that the regulatory subunit of the phosphoinositide 3-kinase (PI3K), p85α, plays a role in mediating UVB-induced VEGF expression in mouse embryonic fibroblasts (MEFs) and mouse epithermal cells, the effect of which is unrelated to the PI3K activity. The transcriptional factor NFAT3 functions as a downstream target of p85α to mediate the induction of VEGF expression in the UVB response. Although lacking NFAT3-binding ability, p85α is required for the recruitment of NFAT3 to the NFAT-response element within the vegf promoter. Furthermore, by identifying the adjacent NFAT- and AP-1-binding sites within the vegf promoter, we also found an induced interaction between NFAT3 and one of the AP-1 components, c-Fos, after UVB irradiation. Without the aid of c-Fos, NFAT3 lost its vegf-promoter-binding ability. Taken together, our results reveal a novel PI3K-independent role for p85α in controlling VEGF induction during the cellular UVB response by regulating NFAT3 activity. Targeting p85α might be helpful for preventing UVB-induced angiogenesis and the associated photodamage.

Suppressing the formation of lipid raft-associated Rac1/PI3K/Akt signaling complexes by curcumin inhibits SDF-1α-induced invasion of human esophageal carcinoma cells

Stromal cell-derived factor-1α (SDF-1α) is a ligand for C-X-C chemokine receptor type 4 (CXCR4), which contributes to the metastasis of cancer cells by promoting cell migration. Here, we show that the SDF-1α/CXCR4 axis can significantly increase invasion of esophageal carcinoma (EC) cells. We accomplished this by examining the effects of CXCR4 knockdown as well as treatment with a CXCR4-neutralizing antibody and the CXCR4-specific inhibitor AMD3100. Curcumin suppressed SDF-1α-induced cell invasion and matrix metalloproteinase-2 (MMP-2) promoter activity, cell surface localization of CXCR4 at lipid rafts, and lipid raft-associated ras-related C3 botulinum toxin substrate 1 (Rac1)/phosphatidylinositol 3-kinase (PI3K) p85α/Akt signaling. Curcumin inhibited SDF-1α-induced cell invasion by suppressing the Rac1-PI3K signaling complex at lipid rafts but did not abrogate lipid raft formation. We further demonstrate that the attenuation of lipid raft-associated Rac1 activity by curcumin was critical for the inhibition of SDF-1α-induced PI3K/Akt/NF-κB activation, cell surface localization of CXCR4 at lipid rafts, MMP-2 promoter activity, and cell invasion. Collectively, our results indicate that curcumin inhibits SDF-1α-induced EC cell invasion by suppressing the formation of the lipid raft-associated Rac1-PI3K-Akt signaling complex, the localization of CXCR4 with lipid rafts at the cell surface, and MMP-2 promoter activity, likely through the inhibition of Rac1 activity.

PIK3R1 (p85α) is somatically mutated at high frequency in primary endometrial cancer

Phosphoinositide 3-kinase (PI3K) is an important therapeutic target. Mutations in PIK3CA, which encodes p110α, the catalytic subunit of PI3K, occur in endometrioid endometrial cancers (EEC) and nonendometrioid endometrial cancers (NEEC). The goal of this study was to determine whether PIK3R1, which encodes p85α, the inhibitory subunit of PI3K, is mutated in endometrial carcinoma. We carried out exonic sequencing of PIK3R1 from 42 EECs and 66 NEECs. The pattern of PIK3R1 mutations was compared with the patterns of PIK3CA, PTEN, and KRAS mutations. The biochemical effect of seven PIK3R1 mutations was examined by stable expression in U2OS cells, followed by coimmunoprecipitation analysis of p110α, and Western blotting of phospho-AKT(Ser473) (p-AKT(Ser473)). We found that PIK3R1 was somatically mutated in 43% of EECs and 12% of NEECs. The majority of mutations (93.3%) were localized to the p85α-nSH2 and -iSH2 domains. Several mutations were recurrent. PIK3R1 mutations were significantly (P = 0.0015) more frequent in PIK3CA-wild type EECs (70%) than in PIK3CA mutant EECs (18%). Introduction of wild-type p85α into U2OS cells reduced the level of p-AKT(Ser473) compared with the vector control. Five p85α mutants, p85αdelH450-E451, p85αdelK459, p85αdelY463-L466, p85αdelR574-T576, and the p85αN564D positive control, were shown to bind p110α and led to increased levels of p-AKT(Ser473). The p85αR348X and p85αK511VfsX2 mutants did not bind p110α and showed no appreciable change in p-AKT(Ser473) levels. In conclusion, our study has revealed a new mode of PI3K alteration in primary endometrial tumors and warrants future studies to determine whether PIK3R1 mutations correlate with clinical outcome to targeted therapies directed against the PI3K pathway in EEC and NEEC.

PI3K/Akt activation is critical for early hepatic regeneration after partial hepatectomy

Hepatic resection is associated with rapid proliferation and regeneration of the remnant liver. Phosphatidylinositol 3-kinase (PI3K), composed of a p85alpha regulatory and a p110alpha catalytic subunit, participates in multiple cellular processes, including cell growth and survival; however, the role of PI3K in liver regeneration has not been clearly delineated. In this study, we used the potent PI3K inhibitor wortmannin and small interfering RNA (siRNA) targeting the p85alpha and p110alpha subunits to determine whether total or selective PI3K inhibition would abrogate the proliferative response of the liver after partial hepatectomy in mice. Hepatic resection is associated with an induction in PI3K activity; total PI3K blockade with wortmannin and selective inhibition of p85alpha or p110alpha with siRNA resulted in a significant decrease in hepatocyte proliferation, especially at the earliest time points. Fewer macrophages and Kupffer cells were present in the regenerating liver of mice treated with wortmannin or siRNA to p85alpha or p110alpha, as reflected by a paucity of F4/80-positive cells. Additionally, PI3K inhibition led to an aberrant architecture in the regenerating hepatocytes characterized by vacuolization, lipid deposition, and glycogen accumulation; these changes were not noted in the sham livers. Our data demonstrate that PI3K/Akt pathway activation plays a critical role in the early regenerative response of the liver after resection; inhibition of this pathway markedly abrogates the normal hepatic regenerative response, most likely by inhibiting macrophage infiltration and cytokine elaboration and thus hepatocyte priming for replication.