Protein-carbohydrate ingestion alters Vps34 cellular localization independent of changes in kinase activity in human skeletal muscle

NEW FINDINGS

What is the central question of the study? Is Vps34 a nutrient-sensitive activator of mTORC1 in human skeletal muscle? What is the main finding and its importance? We show that altering nutrient availability, via protein-carbohydrate feeding, does not increase Vps34 kinase activity in human skeletal muscle. Instead, feeding increased Vps34-mTORC1 co-localization in parallel to increased mTORC1 activity. These findings may have important implications in the understanding nutrient-induced mTORC1 activation in skeletal muscle via interaction with Vps34.

ABSTRACT

The Class III PI3Kinase, Vps34, has recently been proposed as a nutrient sensor, essential for activation of the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1). We therefore investigated the effects of increasing nutrient availability through protein-carbohydrate (PRO-CHO) feeding on Vps34 kinase activity and cellular localization in human skeletal muscle. Eight young, healthy males (21 ± 0.5 yrs, 77.7 ± 9.9 kg, 25.9 ± 2.7 kg/m² , mean ± SD) ingested a PRO-CHO beverage containing 20/44/1 g PRO/CHO/FAT respectively, with skeletal muscle biopsies obtained at baseline and 1 h and 3 h post-feeding. PRO-CHO feeding did not alter Vps34 kinase activity, but did stimulate Vps34 translocation toward the cell periphery (PRE (mean ± SD) - 0.273 ± 0.040, 1 h - 0.348 ± 0.061, Pearson's Coefficient (r)) where it co-localized with mTOR (PRE - 0.312 ± 0.040, 1 h - 0.348 ± 0.069, Pearson's Coefficient (r)). These alterations occurred in parallel to an increase in S6K1 kinase activity (941 ± 466% of PRE at 1 h post-feeding). Subsequent in vitro experiments in C2C12 and human primary myotubes displayed no effect of the Vps34-specific inhibitor SAR405 on mTORC1 signalling responses to elevated nutrient availability. Therefore, in summary, PRO-CHO ingestion does not increase Vps34 activity in human skeletal muscle, whilst pharmacological inhibition of Vps34 does not prevent nutrient stimulation of mTORC1 in vitro. However, PRO-CHO ingestion promotes Vps34 translocation to the cell periphery, enabling Vps34 to associate with mTOR. Therefore, our data suggests that interaction between Vps34 and mTOR, rather than changes in Vps34 activity per se may be involved in PRO-CHO activation of mTORC1 in human skeletal muscle.

Cold Atmospheric Plasma induces accumulation of lysosomes and caspase-independent cell death in U373MG glioblastoma multiforme cells

Room temperature Cold Atmospheric Plasma (CAP) has shown promising efficacy for the treatment of cancer but the exact mechanisms of action remain unclear. Both apoptosis and necrosis have been implicated as the mode of cell death in various cancer cells. We have previously demonstrated a caspase-independent mechanism of cell death in p53-mutated glioblastoma multiforme (GBM) cells exposed to plasma. The purpose of this study was to elucidate the molecular mechanisms involved in caspase-independent cell death induced by plasma treatment. We demonstrate that plasma induces rapid cell death in GBM cells, independent of caspases. Accumulation of vesicles was observed in plasma treated cells that stained positive with acridine orange. Western immunoblotting confirmed that autophagy is not activated following plasma treatment. Acridine orange intensity correlates closely with the lysosomal marker Lyso TrackerTM Deep Red. Further investigation using isosurface visualisation of confocal imaging confirmed that lysosomal accumulation occurs in plasma treated cells. The accumulation of lysosomes was associated with concomitant cell death following plasma treatment. In conclusion, we observed rapid accumulation of acidic vesicles and cell death following CAP treatment in GBM cells. We found no evidence that either apoptosis or autophagy, however, determined that a rapid accumulation of late stage endosomes/lysosomes precedes membrane permeabilisation, mitochondrial membrane depolarisation and caspase independent cell death.

Induction of the cell survival kinase Sgk1: A possible novel mechanism for α-phenyl-N-tert-butyl nitrone in experimental stroke

Nitrones (e.g. α-phenyl-N-tert-butyl nitrone; PBN) are cerebroprotective in experimental stroke. Free radical trapping is their proposed mechanism. As PBN has low radical trapping potency, we tested Sgk1 induction as another possible mechanism. PBN was injected (100 mg/kg, i.p.) into adult male rats and mice. Sgk1 was quantified in cerebral tissue by microarray, quantitative RT-PCR and western analyses. Sgk1^+/+ and Sgk1^-/- mice were randomized to receive PBN or saline immediately following transient (60 min) occlusion of the middle cerebral artery. Neurological deficit was measured at 24 h and 48 h and infarct volume at 48 h post-occlusion. Following systemic PBN administration, rapid induction of Sgk1 was detected by microarray (at 4 h) and confirmed by RT-PCR and phosphorylation of the Sgk1-specific substrate NDRG1 (at 6 h). PBN-treated Sgk1^+/+ mice had lower neurological deficit ( p < 0.01) and infarct volume ( p < 0.01) than saline-treated Sgk1^+/+ mice. PBN-treated Sgk1^-/- mice did not differ from saline-treated Sgk1^-/- mice. Saline-treated Sgk1^-/- and Sgk1^+/+ mice did not differ. Brain Sgk3:Sgk1 mRNA ratio was 1.0:10.6 in Sgk1^+/+ mice. Sgk3 was not augmented in Sgk1^-/- mice. We conclude that acute systemic treatment with PBN induces Sgk1 in brain tissue. Sgk1 may play a part in PBN-dependent actions in acute brain ischemia.

Mechanistic Target of Rapamycin (mTOR) in the Cancer Setting

This special issue on mammalian target of rapamycin (mTOR) explores the importance of mTOR in cell growth control and cancer. Cancer cells often exploit mTOR as a mechanism to enhance their capacity to grow. While protein synthesis is by far the best-characterized mTOR-driven process, this special issue also describes a wider array of mTOR-driven biological processes that cancer cells benefit from, including autophagy, cell cycle control, metabolic transformation, angiogenic signaling, and anabolic processes such as nucleotide biosynthesis and ribosomal biogenesis. Other areas of mTOR signaling covered in these reviews delve into cell migration, inflammation, and regulation of transcription factors linked to cancer progression.

Oncogenic Signalling through Mechanistic Target of Rapamycin (mTOR): A Driver of Metabolic Transformation and Cancer Progression

Throughout the years, research into signalling pathways involved in cancer progression has led to many discoveries of which mechanistic target of rapamycin (mTOR) is a key player. mTOR is a master regulator of cell growth control. mTOR is historically known to promote cell growth by enhancing the efficiency of protein translation. Research in the last decade has revealed that mTOR’s role in promoting cell growth is much more multifaceted. While mTOR is necessary for normal human physiology, cancer cells take advantage of mTOR signalling to drive their neoplastic growth and progression. Oncogenic signal transduction through mTOR is a common occurrence in cancer, leading to metabolic transformation, enhanced proliferative drive and increased metastatic potential through neovascularisation. This review focuses on the downstream mTOR-regulated processes that are implicated in the “hallmarks” of cancer with focus on mTOR’s involvement in proliferative signalling, metabolic reprogramming, angiogenesis and metastasis.

Probing a 3,4'-bis-guanidinium diaryl derivative as an allosteric inhibitor of the Ras pathway

Mutations in the Ras-pathway occur in 40-45% of colorectal cancer patients and these are refractory to treatment with anti-EGFR-targeted therapies. With this in mind, we have studied novel guanidinium-based compounds with demonstrated ability to inhibit protein kinases. We have performed docking studies with several proteins involved in the Ras-pathway and evaluated 3,4'-bis-guanidinium derivatives as inhibitors of B-Raf. Compound 3, the most potent in this series, demonstrated strong cytotoxicity in (WT)B-Raf colorectal cancer cells and also cells with (V600E)B-Raf mutations. Cell death was induced by apoptosis, detected by cleavage of PARP. Compound 3 also potently inhibited ERK1/2 signalling, inhibited EGFR activation, as well as Src, STAT3 and AKT phosphorylation. Mechanistically, compound 3 did not inhibit ATP binding to B-Raf, but direct assay of B-Raf activity was inhibited in vitro. Summarizing, we have identified a novel B-Raf type-III inhibitor that exhibits potent cellular cytotoxicity.

TBX2 represses CST6 resulting in uncontrolled legumain activity to sustain breast cancer proliferation: a novel cancer-selective target pathway with therapeutic opportunities

TBX2 is an oncogenic transcription factor known to drive breast cancer proliferation. We have identified the cysteine protease inhibitor Cystatin 6 (CST6) as a consistently repressed TBX2 target gene, co-repressed through a mechanism involving Early Growth Response 1 (EGR1). Exogenous expression of CST6 in TBX2-expressing breast cancer cells resulted in significant apoptosis whilst non-tumorigenic breast cells remained unaffected. CST6 is an important tumor suppressor in multiple tissues, acting as a dual protease inhibitor of both papain-like cathepsins and asparaginyl endopeptidases (AEPs) such as Legumain (LGMN). Mutation of the CST6 LGMN-inhibitory domain completely abrogated its ability to induce apoptosis in TBX2-expressing breast cancer cells, whilst mutation of the cathepsin-inhibitory domain or treatment with a pan-cathepsin inhibitor had no effect, suggesting that LGMN is the key oncogenic driver enzyme. LGMN activity assays confirmed the observed growth inhibitory effects were consistent with CST6 inhibition of LGMN. Knockdown of LGMN and the only other known AEP enzyme (GPI8) by siRNA confirmed that LGMN was the enzyme responsible for maintaining breast cancer proliferation. CST6 did not require secretion or glycosylation to elicit its cell killing effects, suggesting an intracellular mode of action. Finally, we show that TBX2 and CST6 displayed reciprocal expression in a cohort of primary breast cancers with increased TBX2 expression associating with increased metastases. We have also noted that tumors with altered TBX2/CST6 expression show poor overall survival. This novel TBX2-CST6-LGMN signaling pathway, therefore, represents an exciting opportunity for the development of novel therapies to target TBX2 driven breast cancers.

A role of autophagy in PTP4A3-driven cancer progression

Autophagy, a "self-eating" cellular process, has dual roles in promoting and suppressing tumor growth, depending on cellular context. PTP4A3/PRL-3, a plasma membrane and endosomal phosphatase, promotes multiple oncogenic processes including cell proliferation, invasion, and cancer metastasis. In this study, we demonstrate that PTP4A3 accumulates in autophagosomes upon inhibition of autophagic degradation. Expression of PTP4A3 enhances PIK3C3-BECN1-dependent autophagosome formation and accelerates LC3-I to LC3-II conversion in an ATG5-dependent manner. PTP4A3 overexpression also enhances the degradation of SQSTM1, a key autophagy substrate. These functions of PTP4A3 are dependent on its catalytic activity and prenylation-dependent membrane association. These results suggest that PTP4A3 functions to promote canonical autophagy flux. Unexpectedly, following autophagy activation, PTP4A3 serves as a novel autophagic substrate, thereby establishing a negative feedback-loop that may be required to fine-tune autophagy activity. Functionally, PTP4A3 utilizes the autophagy pathway to promote cell growth, concomitant with the activation of AKT. Clinically, from the largest ovarian cancer data set (GSE 9899, n = 285) available in GEO, high levels of expression of both PTP4A3 and autophagy genes significantly predict poor prognosis of ovarian cancer patients. These studies reveal a critical role of autophagy in PTP4A3-driven cancer progression, suggesting that autophagy could be a potential Achilles heel to block PTP4A3-mediated tumor progression in stratified patients with high expression of both PTP4A3 and autophagy genes.

FLCN, a novel autophagy component, interacts with GABARAP and is regulated by ULK1 phosphorylation

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant condition caused by mutations in the FLCN gene and characterized by benign hair follicle tumors, pneumothorax, and renal cancer. Folliculin (FLCN), the protein product of the FLCN gene, is a poorly characterized tumor suppressor protein, currently linked to multiple cellular pathways. Autophagy maintains cellular homeostasis by removing damaged organelles and macromolecules. Although the autophagy kinase ULK1 drives autophagy, the underlying mechanisms are still being unraveled and few ULK1 substrates have been identified to date. Here, we identify that loss of FLCN moderately impairs basal autophagic flux, while re-expression of FLCN rescues autophagy. We reveal that the FLCN complex is regulated by ULK1 and elucidate 3 novel phosphorylation sites (Ser406, Ser537, and Ser542) within FLCN, which are induced by ULK1 overexpression. In addition, our findings demonstrate that FLCN interacts with a second integral component of the autophagy machinery, GABA(A) receptor-associated protein (GABARAP). The FLCN-GABARAP association is modulated by the presence of either folliculin-interacting protein (FNIP)-1 or FNIP2 and further regulated by ULK1. As observed by elevation of GABARAP, sequestome 1 (SQSTM1) and microtubule-associated protein 1 light chain 3 (MAP1LC3B) in chromophobe and clear cell tumors from a BHD patient, we found that autophagy is impaired in BHD-associated renal tumors. Consequently, this work reveals a novel facet of autophagy regulation by ULK1 and substantially contributes to our understanding of FLCN function by linking it directly to autophagy through GABARAP and ULK1.

Nutrient ingestion increased mTOR signaling, but not hVps34 activity in human skeletal muscle after sprint exercise

Nutrient provision after sprint exercise enhances mammalian target of rapamycin (mTOR) signaling. One suggested that nutrient sensor is the class III phosphatidylinositol 3-kinase, vacuolar protein sorting 34 (Vps34), not previously studied in human skeletal muscle. It is hypothesized that oral ingestion of essential amino acids (EAA) and carbohydrates (Carb) increases Vps34 activity and mTOR signaling in human skeletal (hVps34) muscle after sprint exercise. Nine subjects were performed 3 × 30-sec all-out sprints with or without ingestion of EAA + Carb or placebo drinks in a randomized order with a month interval. Muscle biopsies were performed at rest and 140 min after last sprint and analyzed for p-mTOR, p-p70S6k, p-eEF2 and for hVps34 activity and hVps34 protein content. Venous blood samples were collected and analyzed for amino acids, glucose, lactate, and insulin. During the sprint exercise session, EAA, glucose, and insulin in blood increased significantly more in EAA + Carb than in placebo. P-mTOR and p-p70S6k were significantly increased above rest in EAA + Carb (P = 0.03, P = 0.007) 140 min after last sprint, but not in placebo. Activity and protein expression of hVps34 were not significantly changed from rest in EAA + Carb 140 min after the last sprint. However, hVps34 activity and protein expression tended to increase in placebo (both P = 0.08). In conclusion, on the contrary to the hypothesis, no increase in activation of hVps34 was found following sprint exercise in EAA + Carb condition. In spite of this, the results support an activation of mTOR during this condition. However, this does not exclude the permissive role of hVps34 in mediating the amino acid-induced activation of mTOR and muscle protein synthesis.

Ran is a potential therapeutic target for cancer cells with molecular changes associated with activation of the PI3K/Akt/mTORC1 and Ras/MEK/ERK pathways

PURPOSE

Cancer cells have been shown to be more susceptible to Ran knockdown than normal cells. We now investigate whether Ran is a potential therapeutic target of cancers with frequently found mutations that lead to higher Ras/MEK/ERK [mitogen-activated protein/extracellular signal-regulated kinase (ERK; MEK)] and phosphoinositide 3-kinase (PI3K)/Akt/mTORC1 activities.

EXPERIMENTAL DESIGN

Apoptosis was measured by flow cytometry [propidium iodide (PI) and Annexin V staining] and MTT assay in cancer cells grown under different conditions after knockdown of Ran. The correlations between Ran expression and patient survival were examined in breast and lung cancers.

RESULTS

Cancer cells with their PI3K/Akt/mTORC1 and Ras/MEK/ERK pathways inhibited are less susceptible to Ran silencing-induced apoptosis. K-Ras-mutated, c-Met-amplified, and Pten-deleted cancer cells are also more susceptible to Ran silencing-induced apoptosis than their wild-type counterparts and this effect is reduced by inhibitors of the PI3K/Akt/mTORC1 and MEK/ERK pathways. Overexpression of Ran in clinical specimens is significantly associated with poor patient outcome in both breast and lung cancers. This association is dramatically enhanced in cancers with increased c-Met or osteopontin expression, or with oncogenic mutations of K-Ras or PIK3CA, all of which are mutations that potentially correlate with activation of the PI3K/Akt/mTORC1 and/or Ras/MEK/ERK pathways. Silencing Ran also results in dysregulation of nucleocytoplasmic transport of transcription factors and downregulation of Mcl-1 expression, at the transcriptional level, which are reversed by inhibitors of the PI3K/Akt/mTORC1 and MEK/ERK pathways.

CONCLUSION

Ran is a potential therapeutic target for treatment of cancers with mutations/changes of expression in protooncogenes that lead to activation of the PI3K/Akt/mTORC1 and Ras/MEK/ERK pathways.

Abstract B30: Phosphorylation of c-jun N terminal kinase (JNK) regulates induction of mitochondrial apoptosis by pro-suvival BCL-2 antagoinist obatoclax

Background: Failure to induce apoptosis is a major limitation of conventional chemotherapy for lung cancer. Resistance to apoptosis contributes to this chemoresistant phenotype. New therapeutic strategies are therefore required to bypass block in apoptosis. Obatoclax (obx) is a small molecule inhibitor of pro-survival BCL-2 family proteins currently being clinically evaluated in both small-cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). However, little is known regarding the molecular mechanisms that might underlie sensitivity and resistance to obx. We are addressing this important question by exploring the pharmacodynamics of obx in NSCLC.

Methods: To isolate mitochondria harvested cells were homogenized in ice-cold isolation buffer and the resulting homogenate subjected to differential centrifugation to isolate the mitochondrial fraction. To conduct shRNA transfections, shRNA plasmids targeted against BAX, BAK, BIM and beclin1 were purchased from SA Biosciences (Frederick, MD, USA). H460 cells were transfected with each plasmid and cells were subjected to at least two rounds of selection to create stable clones. For transmission electron microscopy, cells were fixed in double strength TEM fixative (4% paraformaldehyde, 2.5% glutaraldehyde) in 0.1M sodium cacodylate buffer. Samples were analyzed using standard EM procedures. Specific hVps34 Activity was measured in cells deprived of amino acids for 2 hrs in EBSS. Cells were lysed and subjected to immunoprecipitation with anti-hVps34 antibody, and immunocomplexes were assayed for hVps34 lipid kinase activity.

Results: shRNA downregulation of BAX/BAK (H460shBAX/BAK) inhibited obx induced caspase 9/3 cleavage, PARP activation, and mitochondrial outer membrane permeabilization. However obx was equally effective in reducing clonogenic survival, and short term viability (48–72 hrs). Obx induced prolific cytoplasmic vacuolation evident by TEM, and processing of LC3I to LC3II was evident in NSCLC H460 and H1975 cells, and SCLC H196 and H146 cells suggesting induction of autophagy. H460shBAX/BAK clones also displayed unaltered LC3 processing. To determine whether LC3 processing following obx was regulated by beclin1, stable knockdown was acomplished using shRNA. 3 clones were selected and exhibited reduced hVpS34 activity, however obatoclax induced equal clonogenic survival and LC3 processing compared to NT shRNA controls. Neither LC3 nor PARP processing was inhibited by 3MA or wortmannin. Also we observed loss of beclin1 expression following obx. Activation of JNK and ERK have been implicated in beclin1 indpendent mitophagy, while JNK is also a known activator of BAX and BIM. Obx induced phosphorylation of JNK but not ERK, and inhibition of pJNK blocked PARP cleavage. Also, stable knockdown of BIM by shRNA did not significantly alter obx EC50 values. In H727 NSCLC cells resistant to obx induced apoptosis, JNK phosphorylation and LC3II formation was observed but to a significantly lesser extent than sensitive cells.

Summary: JNK phosphorylation regulates obatoclax induced apoptosis, and this activity is reduced in NSCLC cells resistant to obx. LC3 processing was independent of beclin1, thus the roles of Atg5 and 7 in regulating obx induced LC3 processing and cell fate are ongoing and will be presented.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B30.

mVps34 is activated following high-resistance contractions

Following resistance exercise in the fasted state, both protein synthesis and degradation in skeletal muscle are increased. The addition of essential amino acids potentiates the synthetic response suggesting that an amino acid sensor, which is involved in both synthesis and degradation, may be activated by resistance exercise. One such candidate protein is the class 3 phosphatidylinositol 3OH-kinase (PI3K) Vps34. To determine whether mammalian Vps34 (mVps34) is modulated by high-resistance contractions, mVps34 and S6K1 (an index of mTORC1) activity were measured in the distal hindlimb muscles of rats 0.5, 3, 6 and 18 h after acute unilateral high-resistance contractions with the contralateral muscles serving as a control. In the lengthening tibialis anterior (TA) muscle, S6K1 (0.5 h = 366.3 +/- 112.08%, 3 h = 124.7 +/- 15.96% and 6 h = 129.2 +/- 0%) and mVps34 (3 h = 68.8 +/- 15.1% and 6 h = 36.0 +/- 8.79%) activity both increased, whereas in the shortening soleus and plantaris (PLN) muscles the increase was significantly lower (PLN S6K1 0.5 h = 33.1 +/- 2.29% and 3 h = 47.0 +/- 6.65%; mVps34 3 h = 24.5 +/- 7.92%). HPLC analysis of the TA demonstrated a 25% increase in intramuscular leucine concentration in rats 1.5 h after exercise. A similar level of leucine added to C2C12 cells in vitro increased mVps34 activity 3.2-fold. These data suggest that, following high-resistance contractions, mVps34 activity is stimulated by an influx of essential amino acids such as leucine and this may prolong mTORC1 signalling and contribute to muscle hypertrophy.

Multichip vertical-external-cavity surface-emitting lasers: a coherent power scaling scheme

We propose an efficient coherent power scaling scheme, the multichip vertical-external-cavity surface-emitting laser (VECSEL), in which the waste heat generated in the active region is distributed on multi-VECSEL chips such that the pump level at the thermal rollover is significantly increased. The advantages of this laser are discussed, and the development and demonstration of a two-chip VECSEL operating around 970 nm with over 19 W of output power is presented.

hVps34 is a nutrient-regulated lipid kinase required for activation of p70 S6 kinase

Mammalian cells respond to nutrient deprivation by inhibiting energy consuming processes, such as proliferation and protein synthesis, and by stimulating catabolic processes, such as autophagy. p70 S6 kinase (S6K1) plays a central role during nutritional regulation of translation. S6K1 is activated by growth factors such as insulin, and by mammalian target of rapamycin (mTOR), which is itself regulated by amino acids. The Class IA phosphatidylinositol (PI) 3-kinase plays a well recognized role in the regulation of S6K1. We now present evidence that the Class III PI 3-kinase, hVps34, also regulates S6K1, and is a critical component of the nutrient sensing apparatus. Overexpression of hVps34 or the associated hVps15 kinase activates S6K1, and insulin stimulation of S6K1 is blocked by microinjection of inhibitory anti-hVps34 antibodies, overexpression of a FYVE domain construct that sequesters the hVps34 product PI3P, or small interfering RNA-mediated knock-down of hVps34. hVps34 is not part of the insulin input to S6K1, as it is not stimulated by insulin, and inhibition of hVps34 has no effect on phosphorylation of Akt or TSC2 in insulin-stimulated cells. However, hVps34 is inhibited by amino acid or glucose starvation, suggesting that it lies on the nutrient-regulated pathway to S6K1. Consistent with this, hVps34 is also inhibited by activation of the AMP-activated kinase, which inhibits mTOR/S6K1 in glucose-starved cells. hVps34 appears to lie upstream of mTOR, as small interfering RNA knock-down of hVps34 inhibits the phosphorylation of another mTOR substrate, eIF4E-binding protein-1 (4EBP1). Our data suggest that hVps34 is a nutrient-regulated lipid kinase that integrates amino acid and glucose inputs to mTOR and S6K1.

Identification of filamin C as a new physiological substrate of PKBalpha using KESTREL

We detected a protein in rabbit skeletal muscle extracts that was phosphorylated rapidly by PKBa (protein kinase Ba), but not by SGK1 (serum- and glucocorticoid-induced kinase 1), and identified it as the cytoskeletal protein FLNc (filamin C). PKBa phosphorylated FLNc at Ser2213 in vitro, which lies in an insert not present in the FLNa and FLNb isoforms. Ser2213 became phosphorylated when C2C12 myoblasts were stimulated with insulin or epidermal growth factor, and phosphorylation was prevented by low concentrations of wortmannin, at which it is a relatively specific inhibitor of phosphoinositide 3-kinase. PD 184352 [an inhibitor of the classical MAPK (mitogen-activated protein kinase) cascade] and/or rapamycin [an inhibitor of mTOR (mammalian target of rapamycin)] had no effect. Insulin also induced the phosphorylation of FLNc at Ser2213 in cardiac muscle in vivo, but not in cardiac muscle that does not express PDK1 (3-phosphoinositide-dependent kinase 1), the upstream activator of PKB. These results identify the muscle-specific isoform FLNc as a new physiological substrate for PKB.

Exploitation of KESTREL to identify NDRG family members as physiological substrates for SGK1 and GSK3

We detected a protein in rabbit skeletal muscle extracts that was phosphorylated rapidly by SGK1 (serum- and glucocorticoid-induced kinase 1), but not by protein kinase Ba, and identified it as NDRG2 (N-myc downstream-regulated gene 2). SGK1 phosphorylated NDRG2 at Thr330, Ser332 and Thr348 in vitro. All three residues were phosphorylated in skeletal muscle from wild-type mice, but not from mice that do not express SGK1. SGK1 also phosphorylated the related NDRG1 isoform at Thr328, Ser330 and Thr346 (equivalent to Thr330, Ser332 and Thr348 of NDRG2), as well as Thr356 and Thr366. Residues Thr346, Thr356 and Thr366 are located within identical decapeptide sequences GTRSRSHTSE, repeated three times in NDRG1. These threonines were phosphorylated in NDRG1 in the liver, lung, spleen and skeletal muscle of wild-type mice, but not in SGK1-/- mice. Knock-down of SGK1 in HeLa cells using small interfering RNA also suppressed phosphorylation of the threonine residues in the repeat region of NDRG1. The phosphorylation of NDRG1 by SGK1 transformed it into an excellent substrate for GSK3 (glycogen synthase kinase 3), which could then phosphorylate Ser342, Ser352 and Ser362 in the repeat region. Incubation of HeLa cells with the specific GSK3 inhibitor CT 99021 increased the electrophoretic mobility of NDRG1 in HeLa cells, demonstrating that this protein is phosphorylated by GSK3 in cells. Our results identify NDRG1 and NDRG2 as physiological substrates for SGK1, and demonstrate that phosphorylation of NDRG1 by SGK1 primes it for phosphorylation by GSK3.

The respiratory syncytial virus small hydrophobic protein is phosphorylated via a mitogen-activated protein kinase p38-dependent tyrosine kinase activity during virus infection

The phosphorylation status of the small hydrophobic (SH) protein of respiratory syncytial virus (RSV) was examined in virus-infected Vero cells. The SH protein was isolated from [35S]methionine- and [33P]orthophosphate-labelled RSV-infected cells and analysed by SDS-PAGE. In each case, a protein product of the expected size for the SH protein was observed. Phosphoamino acid analysis and reactivity with the phosphotyrosine specific antibody PY20 showed that the SH protein was modified by tyrosine phosphorylation. The role of tyrosine kinase activity in SH protein phosphorylation was confirmed by the use of genistein, a broad-spectrum tyrosine kinase inhibitor, to inhibit SH protein phosphorylation. Further analysis showed that the different glycosylated forms of the SH protein were phosphorylated, as was the oligomeric form of the protein. Phosphorylation of the SH protein was specifically inhibited by the mitogen-activated protein kinase (MAPK) p38 inhibitor SB203580, suggesting that SH protein phosphorylation occurs via a MAPK p38-dependent pathway. Analysis of virus-infected cells using fluorescence microscopy showed that, although the SH protein was distributed throughout the cytoplasm, it appeared to accumulate, at low levels, in the endoplasmic reticulum/Golgi complex, confirming recent observations. However, in the presence of SB203580, an increased accumulation of the SH protein in the Golgi complex was observed, although other virus structures, such as virus filaments and inclusion bodies, remained largely unaffected. These results showed that during RSV infection, the SH protein is modified by an MAPK p38-dependent tyrosine kinase activity and that this modification influences its cellular distribution.

Identification of different specificity requirements between SGK1 and PKBalpha

NDRG1 is phosphorylated by SGK1 (but not PKB) in vivo at three residues each contained within three nonapeptide repeats. Here, we demonstrate that this nonapeptide, like the NDRG1 protein, is phosphorylated by SGK1, but not by PKBalpha or RSK1 in vitro. The inability of PKBalpha and RSK1 to phosphorylate the nonapeptide was traced to residues n+1, n+2 and n-4 (where n is the phosphorylation site). Changing them from Ser, Glu and Ser to Phe, Ala and Pro, respectively, transformed the nonapeptide into an excellent substrate for PKBalpha and RSK1. Our results identify a specific substrate for SGK1 and may facilitate detection of additional physiological substrates for this enzyme.

Analysis of hVps34/hVps15 interactions with Rab5 in vivo and in vitro

The hVps34 phosphatidylinositol (PI) 3-kinase plays an important role in the regulation of vesicular trafficking in the endosomal system. hVps34 associates with a myristylated protein kinase, hVps15. The two proteins are targeting to early endosomal membranes by interactions between hVps15 and activated (GTP-bound) Rab5. This leads to the production of the hVps34 product, PI(3)P, in the endosomal membrane, and subsequent recruitment of FYVE and PX domain-containing effector proteins. This chapter describes the analysis of hVps34/hVps15 interactions with Rab5 in tissue culture cells and in vitro.

Transforming growth factor beta activates Smad2 in the absence of receptor endocytosis

Like many other cell surface receptors, transforming growth factor beta (TGF-beta) receptors are internalized upon ligand stimulation. Given that the signaling-facilitating molecules Smad anchor for receptor activation (SARA) and Hrs are mainly localized in early endosomes, it was unclear whether receptor internalization is required for Smad2 activation. Using reversible biotin labeling, we directly monitored internalization of the TGF-beta type I receptor. Our data indicate that TGF-beta type I receptor is endocytosed via a clathrin-dependent mechanism and is effectively blocked by depletion of intracellular potassium or by expression of a mutant dynamin (K44A). However, blockage of receptor endocytosis by these two means has no effect on TGF-beta-mediated Smad2 activation. Furthermore, TGF-beta-induced Smad2 activation was unaffected by inhibition of hVPS34 activity with wortmannin or inhibitory anti-hVPS34 antibodies. Finally, we demonstrated that Smad2 interacted with cell surface receptors and that a SARA binding-deficient Smad2 mutant was phosphorylated by the receptors. Thus, our findings suggest that receptor endocytosis is dispersible for TGF-beta-mediated activation of Smad2 and that this activation can be mediated by both SARA-dependent and -independent mechanisms.

Role of Rab5 in the recruitment of hVps34/p150 to the early endosome

PI 3-kinases are important regulators of endocytic trafficking. We have previously proposed a model in which the Rab5 GTPase recruits EEA1 to the early endosome both directly, by binding to EEA1, and indirectly, through the recruitment of the p150/hVps34 PI 3-kinase and the production of PI[3]P in the endosomal membrane. In this study we have examined this model in vivo. We find that both endogenous hVps34 and p150 are targeted to enlarged endosomal structures in cells expressing constitutively activated Rab5, where they are significantly colocalized with EEA1. Recombinant fragments of p150 disrupt the endosomal localization of EEA1, showing that p150 is required for EEA1 targeting. We further analyzed the mechanism of GTP-dependent Rab5-p150 binding, and showed the p150 HEAT and WD40 domains are required for binding, whereas deletion of the protein kinase domain increases binding to Rab5. Overexpression of constitutively active Rab5 caused a redistribution of epitope-tagged hVps34 and p150 to Rab5-positive endosomes. However, subcellular fractionation showed that this was not due to a significant recruitment of hVps34 or p150 from the cytosolic to the particulate fraction. These data suggest that the binding of Rab5 to the HEAT/WD40 domains of p150 is important in regulating the localization of hVps34/p150. However, Rab5 does not appear to act by directly recruiting p150/hVps34 complexes from the cytosol to the endosomal membrane.

Mechanism of phosphatidylinositol 3-kinase-dependent increases in BAC1.2F5 macrophage-like cell density in response to M-CSF: phosphatidylinositol 3-kinase inhibitors increase the rate of apoptosis rather than inhibit DNA synthesis

OBJECTIVE AND DESIGN

To determine the role of phosphatidylinositol 3-kinase (PI 3-kinase) in macrophagecolony stimulating factor (M-CSF)-induced macrophage proliferation.

MATERIALS

The M-CSF-dependent BAC1.2F5 murine macrophage cell line was used.

METHODS

PI 3-kinase activity, Protein kinase B activation, increased cell numbers, induction of DNA synthesis and apoptosis were measured in response to serum, M-CSF and PI 3-kinase inhibitors.

RESULTS

Wortmannin or LY294002 inhibited M-CSF-stimulated increases in BAC1.2F5 cell density. Further analysis showed that inhibition of PI 3-kinase had an insignificant effect on DNA synthesis, but significantly induced apoptosis. Other co-factors in serum mediated cell survival and prevented programmed cell death, in a PI 3-kinase-dependent manner. Stimulation of BAC1.2F5 macrophages with M-CSF induced phosphorylation of PKB/Akt as detected by activation-specific antibodies. Activation of PKB/Akt correlated with PI 3-kinase activation, suggesting that the protection from apoptosis in these cells is mediated by PKB/Akt.

CONCLUSIONS

These results indicate that the lack of increase in cell numbers when cells are stimulated with M-CSF in the presence of PI 3-kinase inhibitors is due to a preferential PI 3-kinase requirement for protection against apoptosis, rather than a requirement for PI 3-kinase activation during the proliferation signal.

Specific requirement for the p85-p110alpha phosphatidylinositol 3-kinase during epidermal growth factor-stimulated actin nucleation in breast cancer cells

We have studied the role of phosphatidylinositol 3-kinases (PI 3-kinases) in the regulation of the actin cytoskeleton in MTLn3 rat adenocarcinoma cells. Stimulation of MTLn3 cells with epidermal growth factor (EGF) induced a rapid increase in actin polymerization, with production of lamellipodia within 3 min. EGF-stimulated lamellipodia were blocked by 100 nM wortmannin, suggesting the involvement of a class Ia PI 3-kinase. MTLn3 cells contain equal amounts of p110alpha and p110beta, and do not contain p110delta. Injection of specific inhibitory antibodies to p110alpha induced cell rounding and blocked EGF-stimulated lamellipod extension, whereas control or anti-p110beta antibodies had no effect. In contrast, both antibodies inhibited EGF-stimulated DNA synthesis. An in situ assay for actin nucleation showed that EGF-stimulated formation of new barbed ends was blocked by injection of anti-p110alpha antibodies. In summary, the p110alpha isoform of PI 3-kinase is specifically required for EGF-stimulated actin nucleation during lamellipod extension in breast cancer cells.

Predictors of aspiration pneumonia: how important is dysphagia?

Aspiration pneumonia is a major cause of morbidity and mortality among the elderly who are hospitalized or in nursing homes. Multiple risk factors for pneumonia have been identified, but no study has effectively compared the relative risk of factors in several different categories, including dysphagia. In this prospective outcomes study, 189 elderly subjects were recruited from the outpatient clinics, inpatient acute care wards, and the nursing home care center at the VA Medical Center in Ann Arbor, Michigan. They were given a variety of assessments to determine oropharyngeal and esophageal swallowing and feeding status, functional status, medical status, and oral/dental status. The subjects were followed for up to 4 years for an outcome of verified aspiration pneumonia. Bivariate analyses identified several factors as significantly associated with pneumonia. Logistic regression analyses then identified the significant predictors of aspiration pneumonia. The best predictors, in one or more groups of subjects, were dependent for feeding, dependent for oral care, number of decayed teeth, tube feeding, more than one medical diagnosis, number of medications, and smoking. The role that each of the significant predictors might play was described in relation to the pathogenesis of aspiration pneumonia. Dysphagia was concluded to be an important risk for aspiration pneumonia, but generally not sufficient to cause pneumonia unless other risk factors are present as well. A dependency upon others for feeding emerged as the dominant risk factor, with an odds ratio of 19.98 in a logistic regression model that excluded tube-fed patients.

Division by 3 of optical frequencies by use of difference-frequency generation in noncritically phase-matched RbTiOAsO(4)

A new scheme for coherently connecting optical frequencies in a 3:1 ratio has been demonstrated. To phase lock a Nd:YAG laser at 1064 nm with a CO overtone laser at 3192 nm, we generated their difference frequency in RbTiOAsO(4) (RTA) and beat it against the second harmonic of 3192 nm that was generated in AgGaSe(2).

Decrease of iconic memory after alcohol

Alcohol did not alter the rate of information loss from iconic memory. However, there was a dose-related decrease in the total amount of information reported which was independent of the rate of information loss.

Alcohol and backward masking of visual information

Alcohol increased the time necessary to transfer information from the initial sensory information storage system into the short-term memory system.