The structure and function of p55PIK reveal a new regulatory subunit for phosphatidylinositol 3-kinase

Von Hippel Lindau tumor suppressor controls m6A-dependent gene expression in renal tumorigenesis

N6-Methyladenosine (m6A) is the most abundant posttranscriptional modification, and its contribution to cancer evolution has recently been appreciated. Renal cancer is the most common adult genitourinary cancer, approximately 85% of which is accounted for by the clear cell renal cell carcinoma (ccRCC) subtype characterized by VHL loss. However, it is unclear whether VHL loss in ccRCC affects m6A patterns. In this study, we demonstrate that VHL binds and promotes METTL3/METTL14 complex formation while VHL depletion suppresses m6A modification, which is distinctive from its canonical E3 ligase role. m6A RNA immunoprecipitation sequencing (RIP-Seq) coupled with RNA-Seq allows us to identify a selection of genes whose expression may be regulated by VHL-m6A signaling. Specifically, PIK3R3 is identified to be a critical gene whose mRNA stability is regulated by VHL in a m6A-dependent but HIF-independent manner. Functionally, PIK3R3 depletion promotes renal cancer cell growth and orthotopic tumor growth while its overexpression leads to decreased tumorigenesis. Mechanistically, the VHL-m6A-regulated PIK3R3 suppresses tumor growth by restraining PI3K/AKT activity. Taken together, we propose a mechanism by which VHL regulates m6A through modulation of METTL3/METTL14 complex formation, thereby promoting PIK3R3 mRNA stability and protein levels that are critical for regulating ccRCC tumorigenesis.

Sperm proteomic landscape is altered in breeding bulls with greater sperm DNA fragmentation index

Although, it is well understood that sperm DNA damage is associated with infertility, the molecular details of how damaged sperm DNA affects fertility are not fully elucidated. Since sperm proteins play an important role in fertilization and post-fertilization events, the present study aimed to identify the sperm proteomic alterations in bulls with high sperm DNA Fragmentation Index (DFI%). Semen from Holstein-Friesian crossbred breeding bulls (n = 50) was subjected to Sperm Chromatin Structure Assay. Based on DFI%, bulls were classified into either high- (HDFI; n = 6), or low-DFI (LDFI; n = 6) and their spermatozoa were subjected to high throughput proteomic analysis. Liquid chromatography and mass spectrometry analysis identified 4567 proteins in bull spermatozoa. A total of 2660 proteins were found common to both the groups, while 1193 and 714 proteins were unique to HDFI and LDFI group, respectively. A total of 265 proteins were up regulated and 262 proteins were down regulated in HDFI group. It was found that proteins involved in capacitation [heparin binding (molecular function), ERK1 and ERK2 cascade (biological process), PI3K-Akt signalling (pathway), Jak-STAT signalling (pathway)], spermatogenesis [TLR signalling (pathway), gamete generation (biological process)] and DNA repair mechanism (biological process) were significantly altered in the bulls with high DFI%.

NMDA Receptor-Arc Signaling Is Required for Memory Updating and Is Disrupted in Alzheimer's Disease

BACKGROUND

Memory deficits are central to many neuropsychiatric diseases. During acquisition of new information, memories can become vulnerable to interference, yet mechanisms that underlie interference are unknown.

METHODS

We describe a novel transduction pathway that links the NMDA receptor (NMDAR) to AKT signaling via the immediate early gene Arc and evaluate its role in memory. The signaling pathway is validated using biochemical tools and transgenic mice, and function is evaluated in assays of synaptic plasticity and behavior. The translational relevance is evaluated in human postmortem brain.

RESULTS

Arc is dynamically phosphorylated by CaMKII (calcium/calmodulin-dependent protein kinase II) and binds the NMDAR subunits NR2A/NR2B and a previously unstudied PI3K (phosphoinositide 3-kinase) adapter p55PIK (PIK3R3) in vivo in response to novelty or tetanic stimulation in acute slices. NMDAR-Arc-p55PIK recruits p110α PI3K and mTORC2 (mechanistic target of rapamycin complex 2) to activate AKT. NMDAR-Arc-p55PIK-PI3K-mTORC2-AKT assembly occurs within minutes of exploratory behavior and localizes to sparse synapses throughout hippocampal and cortical regions. Studies using conditional (Nestin-Cre) p55PIK deletion mice indicate that NMDAR-Arc-p55PIK-PI3K-mTORC2-AKT functions to inhibit GSK3 and mediates input-specific metaplasticity that protects potentiated synapses from subsequent depotentiation. p55PIK conditional knockout mice perform normally in multiple behaviors including working memory and long-term memory tasks but exhibit deficits indicative of increased vulnerability to interference in both short-term and long-term paradigms. The NMDAR-AKT transduction complex is reduced in postmortem brain of individuals with early Alzheimer's disease.

CONCLUSIONS

A novel function of Arc mediates synapse-specific NMDAR-AKT signaling and metaplasticity that contributes to memory updating and is disrupted in human cognitive disease.

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.

Discovery of a Highly Potent and Selective Dual PROTAC Degrader of CDK12 and CDK13

Selective degradation of the cyclin-dependent kinases 12 and 13 (CDK12/13) presents a novel therapeutic opportunity for triple-negative breast cancer (TNBC), but there is still a lack of dual CDK12/13 degraders. Here, we report the discovery of the first series of highly potent and selective dual CDK12/13 degraders by employing the proteolysis-targeting chimera (PROTAC) technology. The optimal compound 7f effectively degraded CDK12 and CDK13 with DC50 values of 2.2 and 2.1 nM, respectively, in MDA-MB-231 breast cancer cells. Global proteomic profiling demonstrated the target selectivity of 7f. In vitro, 7f suppressed expression of core DNA damage response (DDR) genes in a time- and dose-dependent manner. Further, 7f markedly inhibited proliferation of multiple TNBC cell lines including MFM223, with an IC50 value of 47 nM. Importantly, 7f displayed a significantly improved antiproliferative activity compared to the structurally similar inhibitor 4, suggesting the potential advantage of a CDK12/13 degrader for TNBC targeted therapy.

Identification of transcription factors and construction of a novel miRNA regulatory network in primary osteoarthritis by integrated analysis

Backgrounds

As osteoarthritis (OA) disease-modifying therapies are not available, novel therapeutic targets need to be discovered and prioritized. Here, we aim to identify miRNA signatures in patients to fully elucidate regulatory mechanism of OA pathogenesis and advance in basic understanding of the genetic etiology of OA.

Methods

Six participants (3 OA and 3 controls) were recruited and serum samples were assayed through RNA sequencing (RNA-seq). And, RNA-seq dataset was analysed to identify genes, pathways and regulatory networks dysregulated in OA. The overlapped differentially expressed microRNAs (DEMs) were further screened in combination with the microarray dataset GSE143514. The expression levels of candidate miRNAs were further validated by quantitative real-time PCR (qRT-PCR) based on the GEO dataset (GSE114007).

Results

Serum samples were sequenced interrogating 382 miRNAs. After screening of independent samples and GEO database, the two comparison datasets shared 19 overlapped candidate micRNAs. Of these, 9 up-regulated DEMs and 10 down-regulated DEMs were detected, respectively. There were 236 target genes for up-regulated DEMs and 400 target genes for those down-regulated DEMs. For up-regulated DEMs, the top 10 hub genes were KRAS, NRAS, CDC42, GDNF, SOS1, PIK3R3, GSK3B, IRS2, GNG12, and PRKCA; for down-regulated DEMs, the top 10 hub genes were NR3C1, PPARGC1A, SUMO1, MEF2C, FOXO3, PPP1CB, MAP2K1, RARA, RHOC, CDC23, and CREB3L2. Mir-584-5p-KRAS, mir-183-5p-NRAS, mir-4435-PIK3R3, and mir-4435-SOS1 were identified as four potential regulatory pathways by integrated analysis.

Conclusions

We have integrated differential expression data to reveal putative genes and detected four potential miRNA-target gene pathways through bioinformatics analysis that represent new mediators of abnormal gene expression and promising therapeutic targets in OA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04894-2.

Role of microRNAs in etiology of azoospermia and their application as non-invasive biomarkers in diagnosis of azoospermic patients

Azoospermia is a common cause of male infertility without any sperm in the semen and consists of ∼1% of all males and ∼15% of infertile ones. Currently, no accurate non-invasive diagnostic method exists for patients with azoospermia and testis biopsy is mandatory to determine if any spermatozoa exist in the testes. Studies have clarified that the expression of some distinct microRNAs shows alterations in azoospermic patients. MicroRNAs play critical roles during spermatogenesis and their dysregulation can defect this process. Here, we review studied microRNAs involved in the pathogenesis of azoospermia and their target genes. Moreover, we will imply the utility of seminal plasma microRNAs as non-invasive diagnostic biomarkers for azoospermia. We hope such studies could help patients with azoospermia in both diagnosis and treatment, in order that they could father their own biological children.

p55PIK deficiency and its NH2-terminal derivative inhibit inflammation and emphysema in COPD mouse model

Chronic obstructive pulmonary disease (COPD) is composed of chronic airway inflammation and emphysema. Recent studies show that Class IA phosphatidylinositol 3-kinases (PI3Ks) play an important role in the regulation of inflammation and emphysema. However, there are few studies on their regulatory subunits. p55PIK is a regulatory subunit of Class IA PI3Ks, and its unique NH₂-terminal gives it special functions. p55PIK expression in the lungs of nonsmokers, smokers, and patients with COPD was examined. We established a fusion protein TAT-N15 from the NH₂-terminal effector sequence of p55PIK and TAT (the transduction domain of HIV transactivator protein) and investigated the effects of silencing p55PIK or adding TAT-N15 on cigarette smoke exposure at the cellular and animal level. p55PIK expression was increased in patients with COPD. p55PIK deficiency and TAT-N15 significantly inhibited the cigarette smoke extract-induced IL-6, IL-8, and activation of the Akt and the NF-κB pathway in BEAS-2B. p55PIK deficiency and TAT-N15 intranasal administration prevented emphysema and the lung function decline in mice exposed to smoke for 6 mo. p55PIK deficiency and TAT-N15 significantly inhibited lung inflammatory infiltration, reduced levels of IL-6 and KC in mice lung homogenate, and inhibited activation of the Akt and the NF-κB signaling in COPD mice lungs. Our studies indicate that p55PIK is involved in the pathogenesis of COPD, and its NH₂-terminal derivative TAT-N15 could be an effective drug in the treatment of COPD by inhibiting the activation of the Akt and the NF-κB pathway.

Signaling roles of phosphoinositides in the retina

The field of phosphoinositide signaling has expanded significantly in recent years. Phosphoinositides (also known as phosphatidylinositol phosphates or PIPs) are universal signaling molecules that directly interact with membrane proteins or with cytosolic proteins containing domains that directly bind phosphoinositides and are recruited to cell membranes. Through the activities of phosphoinositide kinases and phosphoinositide phosphatases, seven distinct phosphoinositide lipid molecules are formed from the parent molecule, phosphatidylinositol. PIP signals regulate a wide range of cellular functions, including cytoskeletal assembly, membrane budding and fusion, ciliogenesis, vesicular transport, and signal transduction. Given the many excellent reviews on phosphoinositide kinases, phosphoinositide phosphatases, and PIPs in general, in this review, we discuss recent studies and advances in PIP lipid signaling in the retina. We specifically focus on PIP lipids from vertebrate (e.g., bovine, rat, mouse, toad, and zebrafish) and invertebrate (e.g., Drosophila, horseshoe crab, and squid) retinas. We also discuss the importance of PIPs revealed from animal models and human diseases, and methods to study PIP levels both in vitro and in vivo. We propose that future studies should investigate the function and mechanism of activation of PIP-modifying enzymes/phosphatases and further unravel PIP regulation and function in the different cell types of the retina.

Altered microRNAs expression levels of sperm and seminal plasma in patients with infertile ejaculates compared with normozoospermic males

Approximately 15% of couples are unable to conceive after one year of unprotected intercourse. Because sperm can be accessed with ease, it is reasonable to search for non-invasive biomarkers in semen. MicroRNAs are a family of short single-stranded non-coding RNA molecules that are capable of regulating gene expression and causing mRNA degradation. We studied the most common 11 spermatogenesis-related microRNAs expression levels in sperm and seminal plasma from patients with oligozoospermic or asthenozoospermic ejaculates, and in men with normozoospermic ejaculates. Five of these miRNAs were significantly upregulated and three were downregulated in infertile males compared to men with normozoospermic ejaculates. A statistically significant negative correlation was found between the sperm concentration and several microRNA expression level (let-7a, miR-7-1-3p, miR-141, miR-200a, and miR-429, p < 0.0001) both in sperm and in seminal plasma. We also found positive correlation between sperm concentration and some miRNA expression levels (miR-15b, miR-34b, and miR-122, p < 0.001) in sperm and in seminal plasma. This is the first study to demonstrate differences between sperm and seminal plasma miRNA expression level and to identify a correlation between the sperm concentration and miRNAs expression level. Therefore, these MiRNAs could have the potential be used as non-invasive biomarkers to diagnose males with impaired sperm production.

A cell-permeable peptide inhibitor of p55PIK signaling alleviates ocular inflammation in mouse models of uveitis

PURPOSE

Previously we developed TAT-N24 as a synthetic cell-permeable peptide inhibitor of p55PIK signaling and demonstrated its anti-inflammatory effects. This study aimed to evaluate the potential of TAT-N24 as a new agent for the treatment of ocular inflammatory diseases.

METHODS

The endotoxin-induced uveitis (EIU) model was established by intravitreal injection of lipopolysaccharide (LPS) in BALB/c mice and experimental autoimmune uveitis (EAU) model was established by subcutaneous injection of a peptide spanning amino acid residues 161-180 of interphotoreceptor retinoid binding protein (IRBP161-180) with complete Freund's adjuvant (CFA) in B10.RIII mice. TAT-N24 was topically administered in EIU model and intraperitoneally administered in EAU model. The severity levels of uveitis were assessed by clinical and histopathological scores. The mRNA levels of inflammatory cytokines in iris-ciliary body (ICB) and retina were analyzed by reverse transcription quantitative polymerase chain reaction (RT-qPCR). The protein levels of inflammatory factors were determined by ELISA or Western blotting.

RESULTS

The results showed that TAT-N24 alleviated clinical signs, decreased inflammatory cell infiltration and the expression of inflammatory cytokines in both EIU and EAU models. Furthermore, protein levels of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in aqueous humor and mRNA and protein levels of NF-κB p65 in the ICB significantly decreased in EIU model. In EAU model, TAT-N24 application induced a significant decrease of IFN-gamma (IFN-γ) and interleukin-17 (IL-17) in the retina, which were secreted by Th1 and Th17 cells, respectively.

CONCLUSION

In conclusion, TAT-N24 suppressed intraocular inflammation in both EIU and EAU models, and the anti-inflammatory effects were mediated by suppressing the expression of inflammatory cytokines by PI3K/NF-κB signaling pathway. TAT-N24 could be potential candidate for the treatment of ocular inflammatory diseases.

P55PIK Regulates P53-Dependent Apoptosis in Cancer Cells by Interacting with P53 DNA-Specific Domain

Purpose

Phosphatidylinositol 3-kinase (PI3K) plays an important role in tumorigenesis by cross-talking with several signaling pathways. p55PIK is a unique regulatory subunit of PI3K and contains an extra 24-residue N-terminal domain (N24). This study aimed to explore the interaction of p55PIK with p53 and the role of p55PIK in regulating p53-dependent apoptosis in cancer cells.

Materials and Methods

The expression of p55PIK was detected in cancer cells, and the interaction of p55PIK with p53 was examined by immunoprecipitation and pull-down assay. The expression of p53-dependent apoptosis-related genes was detected by PCR.

Results

N24 domain of p55PIK interacted with DNA-specific binding domain (DBD) of p53. The increase or decrease of p55PIK expression led to the change of the expression of p53 and p53-regulated genes in cancer cells. Moreover, N24 peptide led to the change of the expression of p53-regulated genes. Moreover, a membrane-permeable N24 peptide enhanced p53-dependent apoptosis induced by methyl methanesulfonate.

Conclusion

Our results reveal a novel mechanism that regulates p53-dependent apoptosis in cancer cells via p55PIK-p53 interaction.

PIK3R3 regulates ZO-1 expression through the NF-kB pathway in inflammatory bowel disease

BACKGROUND AND AIMS

Inflammatory bowel disease (IBD) are the major risk factor for developing colitis associated cancer (CAC). Previously, we have reported that Phosphoinositide-3-kinase regulatory subunit 3 (PIK3R3) was overexpressed in colorectal cancer (CRC), but we don't know the role of PIK3R3 in IBD.

METHODS

We investigated the differential expression of PIK3R3 and ZO-1 in IBD patients by using Immunohistochemical (IHC) and Gene Expression Omnibus (GEO) database analysis. Caco-2 cells were exposed to different conditions to assess protein level changes of PIK3R3 and ZO-1. Caco-2 cell monolayers were transfected with PIK3R3/siPIK3R3 to assess transepithelial electrical resistance. Tight junction protein integrity was assessed by immunoblot and immunofluorescence. For further, intestinal permeability and tight junction protein integrity were assessed in animal study to assess the treatment role of PIK3R3 specific inhibitor TAT-N 15 (N15).

RESULTS

PIK3R3 was increased in IBD patients, and negatively controlled the expression of ZO-1. In vitro, PIK3R3 regulates ZO-1 by activating NF-kB pathway. Overexpression of PIK3R3 in Caco-2 cells decreased transepithelial electrical resistance (TEER), an opposite result was observed in siPIK3R3 cells. In animal study, inhibition of PIK3R3 by N15 contributed to amelioration of DSS-induced intestinal permeability. Mice treated with N15 exhibited less disruption of TJs in colon tissues.

CONCLUSIONS

PIK3R3 was increased in clinical IBD patients with accompanying disruption of ZO-1 expression. Inhibition of PIK3R3 attenuated DSS-induced IBD symptoms in a mouse model. These findings indicated that PIK3R3 could be a therapeutic target for IBD.

Major miRNA Involved in Insulin Secretion and Production in Beta-Cells

Insulin is implicated as a leading factor in glucose homeostasis and an important theme in diabetes mellitus (DM). Numerous proteins are involved in insulin signaling pathway and their dysregulation contributes to DM. microRNAs (miRNAs) as single-strand molecules have a critical effect on gene expression at post-transcriptional levels. Intensive investigation done by DM researchers disclosed that miRNAs have a significant role in insulin secretion by direct targeting numerous proteins engaged in insulin signaling pathway; so, their dysregulation contributes to DM. In this review, we presented some major miRNAs engaged in the insulin production and secretion.

The Opposing Roles of PIK3R1/p85α and PIK3R2/p85β in Cancer

Dysregulation of the PI3K/PTEN pathway is a frequent event in cancer, and PIK3CA and PTEN are the most commonly mutated genes after TP53. PIK3R1 is the predominant regulatory isoform of PI3K. PIK3R2 is an ubiquitous isoform that has been so far overlooked, but data from The Cancer Genome Atlas shows that increased expression of PIK3R2 is also frequent in cancer. In contrast to PIK3R1, which is a tumor-suppressor gene, PIK3R2 is an oncogene. We review here the opposing roles of PIK3R1 and PIK3R2 in cancer, the regulatory mechanisms that control PIK3R2 expression, and emerging therapeutic approaches targeting PIK3R2.

Effective angiogenesis requires regulation of phosphoinositide signaling

Phosphoinositide signaling regulates numerous downstream effectors that mediate cellular processes which influence cell cycle progression, migration, proliferation, growth, survival, metabolism and vesicular trafficking. A prominent role for phosphoinositide 3-kinase, which generates phosphatidylinositol 3,4,5-trisphosphate, a phospholipid that activates a plethora of effectors including AKT and FOXO during embryonic and postnatal angiogenesis, has been described. In addition, phosphatidylinositol 3-phosphate signaling is required for endosomal trafficking, which contributes to vascular remodeling. This review will examine the role phosphoinositide signaling plays in the endothelium and its contribution to sprouting angiogenesis.

PIK3R3 promotes chemotherapeutic sensitivity of colorectal cancer through PIK3R3/NF-kB/TP pathway

Phosphoinositide-3-kinase regulatory subunit 3(PIK3R3) is overexpressed in different types of human cancer. We previously reported the important role of PIK3R3 in colorectal cancer (CRC). However, the prognosis effect of PIK3R3 in CRC is still remaining unclear. In this study, we explored online clinical databases to analyze the prognosis differences between higher and lower expression of PIK3R3 in CRC patients. Interestingly, we found that better disease-free survival (DFS) were occurred in patients with higher expression of PIK3R3, but there is no significant difference in overall survival (OS). For further, we showed that PIK3R3 could enhance 5-FU induced apoptosis by regulating the expression of thymmidine phosphorylase (TP). In conclusion, PIK3R3 could be considered as a predictor of 5-FU sensitivity for personalized treatment, and a therapeutic target for colorectal cancer.

PIK3R3 regulates PPARα expression to stimulate fatty acid β-oxidation and decrease hepatosteatosis

Phosphatidylinositol 3-kinase (PI3K) signaling plays an important role in the regulation of cellular lipid metabolism and non-alcoholic fatty liver disease (NAFLD). However, little is known about the role of the regulatory subunits of PI3K in lipid metabolism and NAFLD. In this study, we characterized the functional role of PIK3R3 in fasting-induced hepatic lipid metabolism. In this study, we showed that the overexpression of PIK3R3 promoted hepatic fatty acid oxidation via PIK3R3-induced expression of PPARα, thus improving the fatty liver phenotype in high-fat diet (HFD)-induced mice. By contrast, hepatic PIK3R3 knockout in normal mice led to increased hepatic TG levels. Our study also showed that PIK3R3-induced expression of PPARα was dependent on HNF4α. The novel PIK3R3-HNF4α-PPARα signaling axis plays a significant role in hepatic lipid metabolism. As the activation of PIK3R3 decreased hepatosteatosis, PIK3R3 can be considered a promising novel target for developing NAFLD and metabolic syndrome therapies.

MicroRNA-432 targeting E2F3 and P55PIK inhibits myogenesis through PI3K/AKT/mTOR signaling pathway

Skeletal muscle is the dominant executant in locomotion and regulator in energy metabolism. Embryonic myogenesis and postnatal muscle growth are controlled by a cascade of transcription factors and epigenetic regulatory mechanisms. MicroRNAs (miRNAs), a family of non-coding RNA of 22 nucleotides in length, post-transcriptionally regulates expression of mRNA by pairing the seed sequence to 3' UTR of target mRNA. Increasing evidence has demonstrated that miRNAs are important regulators in diverse myogenic processes. The profiling of miRNA expression revealed that miR-432 is more enriched in the longissimus dorsi of 35-day-old piglets than that of adult pigs. Our gain of function study showed that miR-432 can negatively regulate both myoblast proliferation and differentiation. Mechanically, we found that miR-432 is able to down-regulate E2F transcription factor 3 (E2F3) to inactivate the expression of cell cycle and myogenic genes. We also identified that phosphatidylinositol 3-kinase regulatory subunit (P55PIK) is another target gene of miR-432 in muscle cells. downregulation of P55PIK by miR-432 leads to inhibition of P55PIK-mediated PI3K/AKT/mTOR signaling pathway during differentiation. The blocking effect of miR-432 on this pathway can be rescued by insulin treatment. Taken together, our findings identified microRNA-432 as a potent inhibitor of myogenesis which functions by targeting E2F3 and P55PIK in muscle cells.

KIT over-expression by p55PIK-PI3K leads to Imatinib-resistance in patients with gastrointestinal stromal tumors

Imatinib is the first-line drug for gastrointestinal stromal tumors (GISTs), as mutated KIT is closely associated with the occurrence of GIST. However, Imatinib resistance (IMA-resistance) occurs inevitably in most GIST patients. Although the over-expression of KIT in GIST is one of the major factors contributing to IMA-resistance, the underlying mechanism is still unclear. In this study, we demonstrate that p55PIK, an isoform of phosphoinositide 3-kinase (PI3K), increases KIT expression, leading to IMA-resistance in GISTs by activating NF-κB signaling pathway. Furthermore, down-regulation of p55PIK significantly decreases KIT expression and re-sensitizes IMA-resistance-GIST cells to Imatinib in vitro and in vivo. Interestingly, the expression of both p55PIK and KIT proteins is significantly increased in tumor samples from IMA-resistance-GIST patients, suggesting that p55PIK up-regulation may be important for IMA-resistance in the clinical setting. Altogether, our data provide evidence that p55PIK-PI3K signaling can contribute to IMA-resistance in GIST by increasing KIT expression. Moreover, p55PIK may be a novel potential drug target for treating tumors that develop IMA-resistance.

Role of the p55-gamma subunit of PI3K in ALK-induced cell migration: RNAi-based selection of cell migration regulators

Recently, unbiased functional genetic selection identified novel cell migration-regulating genes. This RNAi-based functional selection was performed using 63,996 pooled lentiviral shRNAs targeting 21,332 mouse genes. After five rounds of selection using cells with accelerated or impaired migration, shRNAs were retrieved and identified by half-hairpin barcode sequencing using cells with the selected phenotypes. This selection process led to the identification of 29 novel cell migration regulators. One of these candidates, anaplastic lymphoma kinase (ALK), was further investigated. Subsequent studies revealed that ALK promoted cell migration through the PI3K-AKT pathway via the p55γ regulatory subunit of PI3K, rather than more commonly used p85 subunit. Western blot and immunohistochemistry studies using mouse brain tissues revealed similar temporal expression patterns of ALK, phospho-p55γ, and phospho-AKT during different stages of development. These data support an important role for the p55γ subunit of PI3K in ALK-induced cell migration during brain development.

Identification of PI3K regulatory subunit p55γ as a novel inhibitor of vascular smooth muscle cell proliferation and neointimal formation

AIMS

Phosphatidylinositol 3 kinases (PI3Ks) play a pivotal role in vascular physiology and pathophysiology. We aimed to investigate the role of p55γ, a regulatory subunit of PI3Ks, in vascular smooth muscle cell (VSMC) proliferation and neointimal formation.

METHODS AND RESULTS

We identified p55γ as an important factor that suppresses VSMC proliferation and injury-evoked neointimal formation. Western blot and mRNA analyses showed that p55γ expression declined in balloon-injured rat carotid arteries and in response to PDGF-BB and serum treatment in cultured VSMCs. Overexpression of p55γ inhibited, whereas short hairpin RNA knockdown of p55γ promoted PDGF-BB- and serum-induced VSMC proliferation. Importantly, in vivo adenoviral gene transfer of p55γ into carotid arteries attenuated, while knockdown of p55γ enhanced balloon injury-induced neointimal formation. Furthermore, p55γ sequentially up-regulated p53 and p21, resulting in cell-cycle arrest in S phase; small-interfering RNA knockdown of either p53 or p21 blocked p55γ-induced VSMC growth arrest. Mechanistically, p55γ interacted with and stabilized p53 protein by blocking mouse double minute 2 homologue-mediated p53 ubiquitination and degradation, subsequently activating its target gene p21. Concurrently, p55γ up-regulated Bcl-xl expression, resulting in non-apoptotic growth arrest effect.

CONCLUSION

These findings mark p55γ as a novel upstream regulator of the p53-p21 signalling pathway that negatively regulates VSMC proliferation, suggesting that malfunction of p55γ may trigger vascular proliferative disorders.

BMP2-induced chemotaxis requires PI3K p55γ/p110α-dependent phosphatidylinositol (3,4,5)-triphosphate production and LL5β recruitment at the cytocortex

Background

BMP-induced chemotaxis of mesenchymal progenitors is fundamental for vertebrate development, disease and tissue repair. BMP2 induces Smad and non-Smad signalling. Whereas signal transduction via Smads lead to transcriptional responses, non-Smad signalling induces both, transcriptional and immediate/early non-transcriptional responses. However, the molecular mechanisms by which BMP2 facilitates planar cell polarity, cortical actin rearrangements, lamellipodia formation and chemotaxis of mesenchymal progenitors are poorly understood. Our aim was to uncover the molecular mechanism by which BMP2 facilitates chemotaxis via the BMP2-dependent activation of PI3K and spatiotemporal control of PIP3 production important for actin rearrangements at the mesenchymal cell cytocortex.

Results

We unveiled the molecular mechanism by which BMP2 induces non-Smad signalling by PI3K and the role of the second messenger PIP3 in BMP2-induced planar cell polarity, cortical actin reorganisation and lamellipodia formation. By using protein interaction studies, we identified the class Ia PI3K regulatory subunit p55γ to act as a specific and non-redundant binding partner for BMP receptor type II (BMPRII) in concert with the catalytic subunit p110α. We mapped the PI3K interaction to a region within the BMPRII kinase. Either BMP2 stimulation or increasing amounts of BMPRI facilitated p55γ association with BMPRII, but BMPRII kinase activity was not required for the interaction. We visualised BMP2-dependent PIP3 production via PI3K p55γ/p110α and were able to localise PIP3 to the leading edge of intact cells during the process of BMP2-induced planar cell polarity and actin dependent lamellipodia formation. Using mass spectrometry, we found the highly PIP3-sensitive PH-domain protein LL5β to act as a novel BMP2 effector in orchestrating cortical actin rearrangements. By use of live cell imaging we found that knock-down of p55γ or LL5β or pharmacological inhibition of PI3K impaired BMP2-induced migratory responses.

Conclusions

Our results provide evidence for an important contribution of the BMP2-PI3K (p55γ/p110α)- PIP3-LL5β signalling axis in mesenchymal progenitor cell chemotaxis. We demonstrate molecular insights into BMP2-induced PI3K signalling on the level of actin reorganisation at the leading edge cytocortex. These findings are important to better understand BMP2–induced cytoskeletal reorganisation and chemotaxis of mesenchymal progenitors in different physiological or pathophysiological contexts.

PIK3R3 induces epithelial-to-mesenchymal transition and promotes metastasis in colorectal cancer

Class IA PI3K plays an essential role in the invasion and metastasis of cancer. However, the mechanisms and specific functions of PI3K isoforms in tumor invasion and metastasis are not fully understood. We evaluated the role of PIK3R3, a PI3K regulatory subunit encoded by the PIK3R3 gene, in colorectal cancer invasion and metastasis. Clinical specimens and cell lines data show that the expression level of PIK3R3 is associated with colorectal cancer metastasis. Overexpression of PIK3R3 increases tumor migration and invasion in vitro and promotes metastasis of colorectal cancers in vivo. Furthermore, we investigated that the overexpression of PIK3R3 depends on SNAI2, inducing significant epithelial-to-mesenchymal transition (EMT). Downregulation of PIK3R3 reverses this process, which possibly contributes to the enhanced invasive and metastasizing abilities of colorectal cancer cells. In this study, we found that PIK3R3 plays an important role in colorectal cancer metastasis and might be a potential and specific target for therapies against metastatic colorectal cancer.

Altered p53 regulation of miR-148b and p55PIK contributes to tumor progression in colorectal cancer

MicroRNAs are a class of small non-coding RNAs that regulate the expressions of many genes. Previously, we found that the expression of p55PIK, an isoform of phosphatidylinosotol 3-kinase that has important roles in the regulation of cell cycle, is increased significantly in several types of cancer and contributes to the tumor growth. However, the mechanism for this increased p55PIK expression is not well understood. In this study, we show that miR-148b binds specifically to the 3'-untranslated region of p55PIK and significantly suppresses p55PIK expression. MiR-148b overexpression abolished p55PIK stimulation of cell proliferation and cell cycle progression in colorectal cancer (CRC) cell lines and decreased tumor growth in vivo. Furthermore, we demonstrated that p53 directly activates the transcription of miR-148b by binding to its promoter. In CRC cell lines and tissues, p53 expression was associated with miR-148b expression, and both were negatively associated with p55PIK expression. Our study shows that the p53/miR-148b/p55PIK axis has an important role in cell proliferation and tumor growth, and may represent a novel therapeutic target for treating cancers containing p53 mutations or losses.

PLEKHG2/FLJ00018, a Rho family-specific guanine nucleotide exchange factor, is tyrosine phosphorylated via the EphB2/cSrc signaling pathway

PLEKHG2/FLJ00018, a Rho family-specific guanine nucleotide exchange factor (RhoGEF), is activated by heterotrimeric GTP-binding protein (G protein) Gβγ subunits, and in turn activates the small G protein Rac and Cdc42, which have been shown to mediate signaling pathways leading to actin cytoskeletal reorganization. In the present study, we show that co-expression of the constitutively active mutant of cSrc, a non-receptor tyrosine kinase, and PLEKHG2 induced the tyrosine phosphorylation of PLEKHG2 in HEK293 cells. Through deletion and base substitution mutagenesis we have identified Tyr489 of PLEKHG2 as the site phosphorylated by cSrc. Furthermore, using a high-throughput src homology 2 (SH2) domain binding assay, the SH2 domain of ABL1 and the PI 3-kinse regulator subunit (PIK3R3) were identified as candidates for the binding partner of tyrosine-phosphorylated PLEKHG2. The interaction between PLEKHG2 and the full-length of PIK3R3, but not ABL1, occurs in a tyrosine-phosphorylation-dependent manner. Furthermore, PLEKHG2 is tyrosine phosphorylated at Tyr489 by ephrinB2 receptor signaling via cSrc. Investigation of the physiological function of tyrosine phosphorylation at Tyr489 in PLEKHG2 remains a subject for future studies.

Methods to measure the enzymatic activity of PI3Ks

Phosphoinositide-3-kinase (PI3K) signaling has been implicated in a panoply of cellular responses including survival, proliferation, protein synthesis, migration, and vesicular trafficking. In addition, alterations in the enzymatic activity of PI3Ks have been involved in the pathogenesis of multiple diseases, ranging from cancer to chronic inflammation. The emerging interest in PI3K as a pharmacological target has prompted the development of several molecules with inhibitory activity. In this context, the quantification of the second messenger generated by PI3Ks, phosphoinositide-3-phosphate, offers an opportunity to directly test variations in the lipid kinase activity of PI3K in physiological as well as pathological conditions. Here, we will describe common methods to measure the lipid kinase activity of PI3K in vitro and new techniques to follow the production of phosphoinositide-3-phosphate in vivo. These methods are relevant to study the alterations of the PI3K systems at the interface between signaling and oncometabolism.

Changes in phosphatidylinositol 3-kinase 55 kDa gamma expression and subcellular localization may be caspase 6 dependent in paraquat-induced SH-SY5Y apoptosis

The neurotoxin paraquat (PQ) causes apoptosis of dopaminergic neurons in mammalian cell culture and animal models, mimicking an important pathological feature of Parkinson's disease (PD). The phosphoinositide 3-kinase (PI3K)/Akt pathway is critical for several major survival signals in central nervous system neurons. Phosphatidylinositol 3-kinase 55 kDa gamma (p55PIK) is a regulatory subunit of PI3Ks with important roles in cell proliferation, antiapoptosis, and cell cycle progression. However, p55PIK involvement in mechanisms regarding progression and maintenance of neurodegenerative diseases is largely undetermined. We used PQ-induced apoptosis in human dopaminergic SH-SY5Y cells to investigate the association between p55PIK expression levels, subcellular location, and apoptosis. p55PIK expression was reduced in SH-SY5Y cells and p55PIK messenger RNA and protein expression levels were decreased after PQ treatment. Apoptosis induced by PQ was associated with caspase activation and decreased p55PIK expression. Restoration of p55PIK expression was observed after coincubation with a caspase inhibitor. Overexpressed full-length p55PIK in SH-SY5Y and human embryonic kidney 293 cells showed specific distribution in the nucleus and was cleaved in vitro by recombinant caspase 6 (C6), but not C3 and C7. A p55PIK construct lacking 24 N-terminal amino acids (N24) was tested for the presence of a potential C6-recognizable sequence and was found to express its proteins outside the nucleus. The results suggest that p55PIK may be involved in PQ-induced apoptosis signal transduction and that N24 is crucial for p55PIK subcellular localization. Thus, p55PIK could be a substrate of activated C6 during apoptosis, leading to loss of original biological functions and redistribution to disturb cell cycle progression.

Regulated expression of CXCR4 constitutive active mutants revealed the up-modulated chemotaxis and up-regulation of genes crucial for CXCR4 mediated homing and engraftment of hematopoietic stem/progenitor cells

SDF-1/CXCR4 axis plays a principle role in the homing and engraftment of hematopoietic stem/progenitor cells (HSPCs), a process that defines cells ability to reach and seed recipient bone marrow niche following their intravenous infusion. However, the proper functioning of CXCR4 downstream signaling depends upon consistent optimal expression of both SDF-1 ligand and its receptor CXCR4, which in turn is variable and regulated by several factors. The constitutive active mutants of CXCR4 (N119A and N119S) being able to induce autonomous downstream signaling, overcome the limitation of ligand-receptor interaction for induction of CXCR4 signaling. Therefore, we intended to explore their potential in Chemotaxis; a key cellular process which crucially regulates cells homing to bone marrow. In present study, Tet-on inducible gene expression vector system was used for doxycycline inducible regulated transgene expression of CXCR4 active mutants in hematopoietic stem progenitor cell line K-562. Both of these mutants revealed significantly enhanced Chemotaxis to SDF-1 gradient as compared to wild type. Furthermore, gene expression profiling of these genetically engineered cells as assessed by microarray analysis revealed the up-regulation of group of genes that are known to play a crucial role in CXCR4 mediated cells homing and engraftment. Hence, this study suggest the potential prospects of CXCR4 active mutants in research and development aimed to improve the efficiency of cells in the mechanism of homing and engraftment process.

p55PIK transcriptionally activated by MZF1 promotes colorectal cancer cell proliferation

p55PIK, regulatory subunit of class IA phosphatidylinositol 3-kinase (PI3K), plays a crucial role in cell cycle progression by interaction with tumor repressor retinoblastoma (Rb) protein. A recent study showed that Rb protein can localize to the mitochondria in proliferative cells. Aberrant p55PIK expression may contribute to mitochondrial dysfunction in cancer progression. To reveal the mechanisms of p55PIK transcriptional regulation, the p55PIK promoter characteristics were analyzed. The data show that myeloid zinc finger 1, MZF1, is necessary for p55PIK gene transcription activation. ChIP (Chromatin immuno-precipitation) assay shows that MZF1 binds to the cis-element "TGGGGA" in p55PIK promoter. In MZF1 overexpressed cells, the promoter activity, expression of p55PIK, and cell proliferation rate were observed to be significantly enhanced. Whereas in MZF1-silenced cells, the promoter activity and expression of p55PIK and cell proliferation level was statistically decreased. In CRC tissues, MZF1 and p55PIK mRNA expression were increased (P = 0.046, P = 0.047, resp.). A strong positive correlation (Rs = 0.94) between MZF1 and p55PIK mRNA expression was observed. Taken together, we concluded that p55PIK is transcriptionally activated by MZF1, resulting in increased proliferation of colorectal cancer cells.

Genetic and bioinformatic analyses of the expression and function of PI3K regulatory subunit PIK3R3 in an Asian patient gastric cancer library

Background

While there is strong evidence for phosphatidylinositol 3-kinase (PI3K) involvement in cancer development, there is limited information about the role of PI3K regulatory subunits. PIK3R3, the gene that encodes the PI3K regulatory subunit p55γ, is over-expressed in glioblastoma and ovarian cancers, but its expression in gastric cancer (GC) is not known. We thus used genetic and bioinformatic approaches to examine PIK3R3 expression and function in GC, the second leading cause of cancer mortality world-wide and highly prevalent among Asians.

Methods

Primary GC and matched non-neoplastic mucosa tissue specimens from a unique Asian patient gastric cancer library were comprehensively profiled with platforms that measured genome-wide mRNA expression, DNA copy number variation, and DNA methylation status. Function of PIK3R3 was predicted by IPA pathway analysis of co-regulated genes with PIK3R3, and further investigated by siRNA knockdown studies. Cell proliferation was estimated by crystal violet dye elution and BrdU incorporation assay. Cell cycle distribution was analysed by FACS.

Results

PIK3R3 was significantly up-regulated in GC specimens (n = 126, p < 0.05), and 9.5 to 15% tumors showed more than 2 fold increase compare to the paired mucosa tissues. IPA pathway analysis showed that PIK3R3 promoted cellular growth and proliferation. Knockdown of PIK3R3 decreased the growth of GC cells, induced G0/G1 cell cycle arrest, decreased retinoblastoma protein (Rb) phosphorylation, cyclin D1, and PCNA expression.

Conclusion

Using a combination of genetic, bioinformatic, and molecular biological approaches, we showed that PIK3R3 was up-regulated in GC and promoted cell cycle progression and proliferation; and thus may be a potential new therapeutic target for GC.

p85β regulatory subunit of class IA PI3 kinase negatively regulates mast cell growth, maturation, and leukemogenesis

We show that loss of p85α inhibits the growth and maturation of mast cells, whereas loss of p85β enhances this process. Whereas restoring the expression of p85α in P85α(-/-) cells restores these functions, overexpression of p85β has the opposite effect. Consistently, overexpression of p85β in WT mast cells represses KIT-induced proliferation and IL-3-mediated maturation by inhibiting the expression of Microphthalmia transcription factor. Because p85α and p85β differ in their N-terminal sequences, chimeric proteins consisting of amino or carboxy-terminal of p85α and/or p85β do not rescue the growth defects of p85α(-/-) cells, suggesting cooperation between these domains for normal mast cell function. Loss of p85β impaired ligand induced KIT receptor internalization and its overexpression enhanced this process, partly because of increased binding of c-Cbl to p85β relative to p85α. In vivo, loss of p85β resulted in increased mast cells, and bone marrow transplantation of cells overexpressing p85β resulted in significant reduction in some tissue mast cells. Overexpression of p85β suppressed the growth of oncogenic KIT-expressing cells in vitro and prolonged the survival of leukemic mice in vivo. Thus, p85α and p85β differentially regulate SCF and oncogenic KIT-induced signals in myeloid lineage-derived mast cells.

Differential roles for the p101 and p84 regulatory subunits of PI3Kγ in tumor growth and metastasis

Phosphoinositide 3-kinase γ (PI3Kγ) consists of a catalytic subunit p110γ, which forms mutually exclusive dimers with one of the regulatory subunits called p101 and p84/p87(PIKAP). Recently, PI3Kγ emerged as being a potential oncogene because overexpression of the catalytic subunit p110γ or the regulatory subunit p101 leads to oncogenic cellular transformation and malignancy. However, the contribution of the individual subunits to tumor growth and metastasis and the mechanisms involved are not understood. We therefore individually knocked down the PI3Kγ subunits (p84, p101 and p110γ) in MDA-MB-231 cells, which reduced in vitro migration of the cell lines. Knockdown of p110γ or p101 inhibited apoptosis, Akt phosphorylation and lung colonization in SCID mice. Similarly, the knockdown of p110γ and p101 in murine epithelial carcinoma 4T1.2 cells inhibited primary tumor growth and spontaneous metastasis, as well as lung colonization. In contrast, knockdown of p84 in MDA-MB-231 cells enhanced Akt phosphorylation and lung colonization. These findings are the first to implicate differential functions of the two PI3Kγ regulatory subunits in the process of oncogenesis, and indicate that loss of p101 is sufficient to reduce in vivo tumor growth and metastasis to the same extent as that of p110γ.

Biased binding of class IA phosphatidyl inositol 3-kinase subunits to inducible costimulator (CD278)

To better understand T lymphocyte costimulation by inducible costimulator (ICOS; H4; CD278), we analyzed proteins binding to ICOS peptides phosphorylated at the Y(191)MFM motif. Phosphorylated ICOS binds class IA phosphatidyl inositol 3-kinase (PI3-K) p85α, p50-55α and p85β regulatory subunits and p110α, p110δ and p110β catalytic subunits. Intriguingly, T cells expressed high levels of both p110α or p110δ catalytic subunits, yet ICOS peptides, cell surface ICOS or PI3-kinase class IA regulatory subunits preferentially coprecipitated p110α catalytic subunits. Silencing p110α or p110δ partially inhibited Akt/PKB activation induced by anti-CD3 plus anti-ICOS antibodies. However, silencing p110α enhanced and silencing p110δ inhibited Erk activation. Both p110α- and p110δ-specific inhibitors blocked cytokine secretion induced by TCR/CD3 activation with or without ICOS costimulus, but only p110α inhibitors blocked ICOS-induced cell elongation. Thus, p110α and p110δ are essential to optimal T cell activation, but their abundance and activity differentially tune up distinct ICOS signaling pathways.

Phosphoinositide 3-kinase signaling in retinal rod photoreceptors

PURPOSE

Phosphoinositide 3-kinase (PI3K) consists of a p110 catalytic protein and a p85α regulatory protein, required for the stabilization and localization of p110-PI3K activity. The biological significance of PI3K was investigated in vertebrate rod photoreceptors by deleting its regulatory p85α protein and examining its role in photoreceptor structure, function, and protein trafficking.

METHODS

Mice that expressed Cre recombinase in rods were bred to mice with a floxed p85α (pik3r1) regulatory subunit of PI3K to generate a conditional deletion of pik3r1 in rods. Functional and structural changes were determined by ERG and morphometric analysis, respectively. PI3K activity was measured in retinal homogenates immunoprecipitated with an anti-PY antibody. Akt activation was determined by Western blot analysis with a pAkt antibody.

RESULTS

Light-induced stress increased PI3K activity in retinal immunoprecipitates and phosphorylation of Akt. There was no effect of pik3r1 deletion on retinal structure. However, twin flash electroretinography revealed a slight delay in recovery kinetics in pik3r1 knockout (KO) mice compared with wild-type controls. The movement of arrestin in the pik3r1 KO mice was slower than that in the wild-type mouse retinas at 5 minutes of exposure to light. At 10 minutes of exposure, the ROS localization of arrestin was almost identical between the wild-type and pik3r1 KO mice.

CONCLUSIONS

The results provide the first direct evidence that rods use PI3K-generated phosphoinositides for photoreceptor function. The lack of phenotype in pik3r1 KO rod photoreceptors suggests a redundant role in controlling PIP(3) synthesis.

Regulatory subunits of class IA PI3K

All class I PI3K enzymes are obligate heterodimers, consisting of a catalytic subunit tightly bound to a regulatory subunit. The regulatory subunit influences the subcellular location, binding partners, and activity of the catalytic subunit. Regulatory subunits also possess adaptor functions in cellular signaling, which are largely independent of their role in regulating PI3K activity. This chapter reviews the structure and function of PI3K regulatory subunits, focusing on the class IA subgroup.

PI 3-kinase regulatory subunits as regulators of the unfolded protein response

The endoplasmic reticulum (ER) consists of an interconnected, membranous network that is the major site for the synthesis and folding of integral membrane and secretory proteins. Within the ER lumen, protein folding is facilitated by molecular chaperones and a variety of enzymes that ensure that polypeptides obtain their appropriate, tertiary conformation (Dobson, C. M. (2004). Principles of protein folding, misfolding and aggregation. Semin. Cell Dev. Biol. 15, 3-16; Ni, M., and Lee, A. S. (2007). ER chaperones in mammalian development and human diseases. FEBS Lett. 581, 3641-3651.). Physiological conditions that increase protein synthesis or stimuli that disturb the processes by which proteins obtain their native conformation, create an imbalance between the protein-folding demand and capacity of the ER. This results in the accumulation of unfolded or improperly folded proteins in the ER lumen and a state of ER stress. The cellular response, referred to as the unfolded protein response (UPR), results in activation of three linked signal transduction pathways: PKR-like kinase (PERK), inositol requiring 1 α (IRE1α), and activating transcription factor 6α (ATF6α) (Ron, D., and Walter, P. (2007). Signal integration in the endoplasmic reticulum unfolded protein response. Nat. Rev. Mol. Cell. Biol. 8, 519-529; Schroder, M., and Kaufman, R. (2005). ER stress and the unfolded protein response. Mutat. Res./Fundam. Mol. Mech. Mutagen. 569, 29-63.). Collectively, the combined actions of these signaling cascades serve to reduce ER stress through attenuation of translation to reduce protein synthesis and through activation of transcriptional programs that ultimately serve to increase ER protein-folding capacity. Recently, we and Park et al. have characterized a novel function for the p85α and p85β subunits as modulators of the UPR by virtue of their ability to facilitate the nuclear entry of XBP-1s following induction of ER stress (Park, S. W., Zhou, Y., Lee, J., Lu, A., Sun, C., Chung, J., Ueki, K., and Ozcan, U. (2010). Regulatory subunits of PI3K, p85alpha and p85 beta, interact with XBP1 and increase its nuclear translocation. Nat. Med. 16, 429-437; Winnay, J. N., Boucher, J., Mori, M. A., Ueki, K., and Kahn, C. R. (2010). A regulatory subunit of phosphoinositide 3-kinase increases the nuclear accumulation of X-box-binding protein-1 to modulate the unfolded protein response. Nat. Med. 16, 438-445.). This chapter describes the recently elucidated role for the regulatory subunits of PI 3-kinase as modulators of the UPR and provides methods to measure UPR pathway activation.

Phosphoinositide 3-kinase signaling in the vertebrate retina

The phosphoinositide (PI) cycle, discovered over 50 years ago by Mabel and Lowell Hokin, describes a series of biochemical reactions that occur on the inner leaflet of the plasma membrane of cells in response to receptor activation by extracellular stimuli. Studies from our laboratory have shown that the retina and rod outer segments (ROSs) have active PI metabolism. Biochemical studies revealed that the ROSs contain the enzymes necessary for phosphorylation of phosphoinositides. We showed that light stimulates various components of the PI cycle in the vertebrate ROS, including diacylglycerol kinase, PI synthetase, phosphatidylinositol phosphate kinase, phospholipase C, and phosphoinositide 3-kinase (PI3K). This article describes recent studies on the PI3K-generated PI lipid second messengers in the control and regulation of PI-binding proteins in the vertebrate retina.

A novel interaction between fibroblast growth factor receptor 3 and the p85 subunit of phosphoinositide 3-kinase: activation-dependent regulation of ERK by p85 in multiple myeloma cells

Ectopic activation of fibroblast growth factor receptor 3 (FGFR3) is associated with several cancers, including multiple myeloma (MM). FGFR3 inhibition in these cells inhibits proliferation and induces apoptosis, validating FGFR3 signaling as a therapeutic target in t(4;14) MM cases. We have identified the PI3K regulatory subunit, p85alpha, as a novel interactor of FGFR3 by yeast two-hybrid, and confirmed an interaction with both p85alpha and p85beta in mammalian cells. The interaction of FGFR3 with p85 is dependent upon receptor activation. In contrast to the Gab1-mediated association of FGFRs with p85, the FGFR3-p85 interaction we observed requires FGFR3 Y760, previously identified as a PLCgamma binding site. The interaction of p85 with FGFR3 does not require PLCgamma, suggesting the p85 interaction is direct and independent of PLCgamma binding. FGFR3 and p85 proteins also interact in MM cell lines which consistently express p85alpha and p85beta, but not p50 or p55 subunits. siRNA knockdown of p85beta in MM cells caused an increased ERK response to FGF2. These data suggest that an endogenous negative regulatory role for the p85-FGFR3 interaction on the Ras/ERK/MAPK pathway may exist in response to FGFR3 activity and identifies a novel therapeutic target for MM.

Lower phosphoinositide 3-kinase (PI 3-kinase) activity and differential expression levels of selective catalytic and regulatory PI 3-kinase subunit isoforms in prefrontal cortex and hippocampus of suicide subjects

Phosphoinositide 3 (PI 3)-kinase is one of the key signaling enzymes that participates in a myriad of physiological functions in brain and is utilized by neurotrophins to mediate neuronal plasticity, cell survival, and inhibition of apoptosis for several neuronal subtypes. Our recent demonstration that expression of neurotrophic factors and activation of the receptor tyrosine kinase B are significantly altered in postmortem brain of suicide subjects led us to examine whether suicide brain is associated with alterations in PI 3-kinase signaling. In prefrontal cortex (PFC), hippocampus, and cerebellum of suicide (n=28) and nonpsychiatric control (n=21) subjects we examined catalytic activation of PI 3-kinase, and mRNA and protein levels of regulatory (p85alpha, p85beta) and catalytic (p110alpha, p110beta) subunits of PI 3-kinase. It was observed that the catalytic activity of PI 3-kinase was significantly reduced in PFC and hippocampus of suicide subjects compared with nonpsychiatric control subjects. Competitive PCR analysis revealed significantly reduced mRNA expression of p85beta and p110alpha and increased expression of p85alpha subunit isoforms in PFC and hippocampus of suicide subjects. Alterations in these catalytic and regulatory subunits were accompanied by changes in their respective protein levels. These changes were not present in cerebellum of suicide subjects. Also, these changes were present in all suicide subjects irrespective of psychiatric diagnosis. Our findings of reduced activation and altered expression of specific PI 3-kinase regulatory and catalytic subunit isoforms demonstrate abnormalities in this signaling pathway in postmortem brain of suicide subjects and suggest possible involvement of aberrant PI 3-kinase signaling in the pathogenic mechanisms of suicide.

PI3K signaling effects in hypothalamic neurons mediated by estrogen

Multiple mechanisms mediate the effects of estrogen in the central nervous system, including signal transduction pathways such as protein kinase A, protein kinase C, and phosphatidylinositol 3-kinase (PI3K) pathways. Previously we demonstrated that estrogen regulates a number of PI3K-related genes in the hypothalamus, including the PI3K p55gamma regulatory subunit. We hypothesized that PI3K activation is critical for the effects of estrogen and that the p55gamma subunit may be more prevalent than the p85alpha regulatory subunit in the hypothalamus. Therefore, in the present study, we compared the mRNA distribution of the p55gamma and p85alpha regulatory subunits by using in situ hybridization in guinea pig. Expression level of p55gamma mRNA was greater than p85alpha in most hypothalamic nuclei. Twenty-four hours of estrogen treatment increased p55gamma mRNA expression in the paraventricular, suprachiasmatic, arcuate, and ventromedial nuclei, and little or no change was observed for p85alpha mRNA. Quantitative real-time PCR confirmed the in situ hybridization results. Next, we investigated the general role of PI3K signaling in the estrogen-mediated changes of arcuate proopiomelanocortin (POMC) neuronal excitability by using whole-cell recording. One cellular mechanism by which estrogen increases neuronal excitability is to desensitize (uncouple) gamma-aminobutyric acid type B (GABA(B)) receptors from their G-protein-gated inwardly rectifying K(+) channels in hypothalamic neurons. We found that the PI3K inhibitors wortmannin and LY294002 significantly reduced the estrogen-mediated GABA(B) receptor desensitization in POMC arcuate neurons, suggesting that PI3K signaling is a critical downstream mediator of the estrogen-mediated rapid effects. Collectively, these data suggest that the interplay between estrogen and PI3K occurs at multiple levels, including transcriptional and membrane-initiated signaling events that ultimately lead to changes in homeostatic function.