Induction Of Phosphatase Activity Research Articles

Transcriptional and Morpho-Physiological Responses of Marchantia polymorpha upon Phosphate Starvation.

Phosphate (Pi) is a pivotal nutrient that constraints plant development and productivity in natural ecosystems. Land colonization by plants, more than 470 million years ago, evolved adaptive mechanisms to conquer Pi-scarce environments. However, little is known about the molecular basis underlying such adaptations at early branches of plant phylogeny. To shed light on how early divergent plants respond to Pi limitation, we analyzed the morpho-physiological and transcriptional dynamics of Marchantia polymorpha upon Pi starvation. Our phylogenomic analysis highlights some gene networks present since the Chlorophytes and others established in the Streptophytes (e.g., PHR1–SPX1 and STOP1–ALMT1, respectively). At the morpho-physiological level, the response is characterized by the induction of phosphatase activity, media acidification, accumulation of auronidins, reduction of internal Pi concentration, and developmental modifications of rhizoids. The transcriptional response involves the induction of MpPHR1, Pi transporters, lipid turnover enzymes, and MpMYB14, which is an essential transcription factor for auronidins biosynthesis. MpSTOP2 up-regulation correlates with expression changes in genes related to organic acid biosynthesis and transport, suggesting a preference for citrate exudation. An analysis of MpPHR1 binding sequences (P1BS) shows an enrichment of this cis regulatory element in differentially expressed genes. Our study unravels the strategies, at diverse levels of organization, exerted by M. polymorpha to cope with low Pi availability.

Dephosphorylation of the Retinoblastoma protein (Rb) inhibits cancer cell EMT via Zeb

ABSTRACTThe tumor suppressor Retinoblastoma (Rb) protein is highly phosphorylated in cancer cells largely due to the overexpression of cyclins or the loss of expression of cyclin dependent kinase inhibitors (cdki). Hyperphosphorylation of Rb promotes proliferation, and plays a role in the regulation of apoptosis. Recently, inhibition of cyclin dependent activity toward Rb has been identified as a strategy that has shown clinical efficacy. We utilized a method to induce phosphatase activity toward Rb in cells by shRNA silencing of PNUTS (Phosphatase Nuclear Targeting Subunit) that regulates PP1-mediated dephosphorylation of Rb. In this study, the effect of Rb dephosphorylation on the epithelial to mesenchymal transition (EMT) was determined. The EMT transition is observed in cancer cells that have acquired invasive characteristics. In breast cancer cells grown in 3D Matrigel cultures, MCF7 cells undergo apoptosis in response to Rb dephosphorylation, whereas MDA-MB-231 and Hs578T cells exhibit a reduction in the EMT. Cells devoid of phosphorylated Rb (nontransformed MCF10A and Rb-null MDA-MB-468) lacked any response to PNUTS depletion, showing the effect is Rb-dependent. In addition, these studies showed that Rb dephosphorylation in 3D Matrigel cultures of highly invasive HT1080 cells led to the inhibition of the EMT. Furthermore we observed association between dephosphorylated Rb with ZEB1, a zinc-finger E-box-binding transcription factor that regulates expression of E- and N-cadherins. Finally Rb dephosphorylation led to inhibition of ZEB1 transcriptional activity, this data supports the notion that Rb dephosphorylation modulates the EMT. These studies suggest targeting Rb phosphorylation in mesenchymal cancer cells may decrease invasiveness.

Overexpression of PTEN suppresses lipopolysaccharide-induced lung fibroblast proliferation, differentiation and collagen secretion through inhibition of the PI3-K-Akt-GSK3beta pathway

BackgroundAbnormal and uncontrolled proliferation of lung fibroblasts may contribute to pulmonary fibrosis. Lipopolysaccharide (LPS) can induce fibroblast proliferation and differentiation through activation of phosphoinositide3-Kinase (PI3-K) pathway. However, the detail mechanism by which LPS contributes to the development of lung fibrosis is not clearly understood. To investigate the role of phosphatase and tensin homolog (PTEN), a PI3-K pathway suppressor, on LPS-induced lung fibroblast proliferation, differentiation, collagen secretion and activation of PI3-K, we transfected PTEN overexpression lentivirus into cultured mouse lung fibroblasts with or without LPS treatment to evaluate proliferation by MTT and Flow cytometry assays. Expression of PTEN, alpha-smooth muscle actin (alpha-SMA), glycogen synthase kinase 3 beta (GSK3beta) and phosphorylation of Akt were determined by Western-blot or real-time RT-PCR assays. The PTEN phosphorylation activity was measured by a malachite green-based assay. The content of C-terminal propeptide of type I procollagen (PICP) in cell culture supernatants was examined by ELISA.ResultsWe found that overexpression of PTEN effectively increased expression and phosphatase activity of PTEN, and concomitantly inhibited LPS-induced fibroblast proliferation, differentiation and collagen secretion. Phosphorylation of Akt and GSK3beta protein expression levels in the LPS-induced PTEN overexpression transfected cells were significantly lower than those in the LPS-induced non-transfected cells, which can be reversed by the PTEN inhibitor, bpV(phen).ConclusionsCollectively, our results show that overexpression and induced phosphatase activity of PTEN inhibits LPS-induced lung fibroblast proliferation, differentiation and collagen secretion through inactivation of PI3-K-Akt-GSK3beta signaling pathways, which can be abrogated by a selective PTEN inhibitor. Thus, expression and phosphatase activity of PTEN could be a potential therapeutic target for LPS-induced pulmonary fibrosis. Compared with PTEN expression level, phosphatase activity of PTEN is more crucial in affecting lung fibroblast proliferation, differentiation and collagen secretion.

Increased Receptor Stimulation Elicits Differential Calcium-sensing ReceptorT888 Dephosphorylation

The calcium-sensing receptor (CaR) elicits oscillatory Ca(2+)(i) mobilization associated with dynamic, inhibitory protein kinase C-mediated phosphorylation of CaR(T888). While modest CaR stimulation elicits Ca(2+)(i) oscillations, greater stimulation either increases oscillation frequency or elicits sustained responses by an unknown mechanism. Here, moderate CaR stimulation (2.5 mm Ca(2+)(o), 10 min) increased CaR(T888) phosphorylation (160-kDa mature receptor) 5-fold in CaR stably transfected HEK-293 cells, whereas 3-5 mm Ca(2+)(o) treatments were without apparent effect. Treatment with 2 mm Ca(2+)(o) caused sustained CaR(T888) phosphorylation (> or = 20 min) and oscillatory Ca(2+)(i) mobilization. However, 5 mm Ca(2+)(o) increased CaR(T888) phosphorylation only briefly while eliciting sustained Ca(2+)(i) mobilization, suggesting that greater CaR activation induces rapid CaR(T888) dephosphorylation, thus permitting sustained Ca(2+)(i) responses. Indeed, 5 mm Ca(2+)(o) stimulated protein phosphatase 2A activity and induced CaR(T888) dephosphorylation following acute phorbol ester pretreatment, the latter effect being mimicked by CaR-positive allosteric modulators (NPS-R467 and l-Phe). Finally, the phosphatase inhibitor calyculin-A reversed CaR-induced inhibition of parathyroid hormone secretion from bovine parathyroid slices and normal human parathyroid cells, demonstrating the physiological importance of phosphorylation status on parathyroid function. Therefore, high Ca(2+)(o)-stimulated protein kinase C acts in concert with high Ca(2+)(o)-induced phosphatase activity to generate and maintain CaR-induced Ca(2+)(i) oscillations via the dynamic phosphorylation and dephosphorylation of CaR(T888).

S-phase arrest by reactive nitrogen species is bypassed by okadaic acid, an inhibitor of protein phosphatases PP1/PP2A

In mammalian cells DNA damage activates a checkpoint that halts progression through S phase. To determine the ability of nitrating agents to induce S-phase arrest, mouse C10 cells synchronized in S phase were treated with nitrogen dioxide (NO 2) or SIN-1, a generator of reactive nitrogen species (RNS). SIN-1 or NO 2 induced S-phase arrest in a dose- and time-dependent manner. As for the positive controls adozelesin and cisplatin, arrest was accompanied by phosphorylation of ATM kinase; dephosphorylation of pRB; decreases in RF-C, cyclin D1, Cdc25A, and Cdc6; and increases in p21. Comet assays indicated that RNS induce minimal DNA damage. Moreover, in a cell-free replication system, nuclei from cells treated with RNS were able to support control levels of DNA synthesis when incubated in cytosolic extracts from untreated cells, whereas nuclei from cells treated with cisplatin were not. Induction of phosphatase activity may represent one mechanism of RNS-induced arrest, for the PP1/PP2A phosphatase inhibitor okadaic acid inhibited dephosphorylation of pRB; prevented decreases in the levels of RF-C, cyclin D1, Cdc6, and Cdc25A; and bypassed arrest by SIN-1 or NO 2, but not cisplatin or adozelesin. Our studies suggest that RNS may induce S-phase arrest through mechanisms that differ from those elicited by classical DNA-damaging agents.

Induction of phosphorus deficiency and phosphatase activity by salinity (NaCl) stress in Gracilaria tenuistipitata (Gigartinales, Rhodophyta)

The role of phosphorus (P) deficiency in the induction of phosphatase activity by salinity stress has been investigated in a brackish red macroalga Gracilaria tenuistipitata var. liui Zhang et Xia by determining changes in the intracellular concentrations of P and the specific activities of cellular acid (ACP; EC 3.1.3.2) and alkaline (AP; EC 3.1.3.1) phosphatases in response to varying salinity (adjusted by increasing or decreasing NaCI concentration in artificial seawater). After 4 d exposure to salinity ranging from 12 to 75 practical salinity units (psu), the net photosynthetic rate, specific growth rate, and P concentrations were found to be highest at 25 psu and lower as salinity decreased or increased. Unlike the 25 psu treatment, net photosynthetic rate, specific growth rate, and P concentrations in algae grown at 12 or 75 psu was not recovered by NaH2PO4 (60 μM) supplementation, indicating that the availability of P was restricted under both hyposaline and hypersaline conditions. The specific activities of both ACP and AP were higher when exposed to low salinity, especially at 12 psu. The specific activities of both APC (r2 = 0.75, p < 0.05) and AP (r2 = 0.84, p < 0.05) were inversely related to the logarithm of salinity (12–75 psu). Time-course experiments showed that compared to a constant level at 25 psu, the intracellular concentrations of P decreased to a plateau 1 d after exposure to 12 psu, and concomitantly, the specific activities of both ACP and AP increased, the phosphatase activities showing an inverse relationship to P concentrations. When exposed to 55 psu, the specific activities of both ACP and AP showed a transient increase with a peak around 12 h, whereas the concentrations of P decreased rapidly to a plateau after 1 d. The pattern in changes of ACP- and AP-specific activities was different in hyposaline and hypersaline conditions. The present results suggest that the limitation of P may be associated with the induction of cellular phosphatase activities by hyposaline stress in Gracilaria tenuistipitata. The relationships between hypersaline stress and a transient increase of cellular phosphatase activity are discussed.

Induction of a retinoblastoma phosphatase activity by anticancer drugs accompanies p53-independent G1 arrest and apoptosis.

DNA-damaging agents induce accumulation of the tumor suppressor and G1 checkpoint protein p53, leading cells to either growth arrest in G1 or apoptosis (programmed cell death). The p53-dependent G1 arrest involves induction of p21 (also called WAF1/CIP1/SDI1), which prevents cyclin kinase-mediated phosphorylation of retinoblastoma protein (RB). Recent studies suggest a p53-independent G1 checkpoint as well; however, little is known about its molecular mechanisms. We report that induction of a protein-serine/threonine phosphatase activity by DNA damage signals is at least one of the mechanisms responsible for p53-independent, RB-mediated G1 arrest and consequent apoptosis. When two p53-null human leukemic cell lines (HL-60 and U-937) were treated with a variety of anticancer agents, RB became hypophosphorylated, accompanied with G1 arrest. This was followed immediately (in less than 30 min) by apoptosis, as determined by the accumulation of pre-G1 apoptotic cells and the internucleosomal fragmentation of DNA. Addition of calyculin A or okadaic acid (specific serine/threonine phosphatase inhibitors) or zinc chloride (apoptosis inhibitor) prevented the G1 arrest- and apoptosis-specific RB dephosphorylation. The levels of cyclin E- and cyclin A-associated kinase activities remained high during RB dephosphorylation, supporting the involvement of a chemotherapy-induced serine/threonine phosphatase(s) rather than p21. Furthermore, the induced phosphatase activity coimmunoprecipitated with the hyperphosphorylated RB and was active in a cell-free system that reproduced the growth arrest- and apoptosis-specific RB dephosphorylation, which was inhibitable by calyculin A but not zinc. We propose that the RB phosphatase(s) might be one of the p53-independent G1 checkpoint regulators.

Induction of Soluble Phosphatases under Ionic and Non-ionic Osmotic Stresses in Wheat

Summary The effects of phosphorus deficiency, salt stress (NaCl) and non-ionic osmotic stresses (caused by mannitol or polyethylene glycol) were compared in plants and calli of wheat varieties differing in salt and drought tolerance. In calli, phosphorus deficiency induced a high increase in soluble acid phosphatase activity; under osmotic stress conditions a similar increase was found only in cells subjected to NaCl, while in cells grown in the presence of mannitol, phosphatase activity did not change. In wheat seedlings, phosphatase activity increased both in roots and shoots under phosphorus deficiency and, especially in the shoot, under salt and non-ionic osmotic stresses as well. Contrary to phosphorus deficient conditions, the induction of phosphatase activity under ionic and non-ionic osmotic stresses was not accompanied by a decrease in phosphorus content. These results suggest that the induction of acid phosphatase under osmotic and salt stresses may have a cause other than a low phosphate level. The Mg2+ activated alkaline phosphatase activity specific for the shoot decreased under all stress conditions.

Phosphate-starvation response in plant cells: de novo synthesis and degradation of acid phosphatases.

Induction of phosphatase activity is an important component of the plant cell response to phosphate deficiency. Suspension cell cultures of Brassica nigra contain two major inducible acid phosphatase (APase) isozymes; vacuolar phosphoenolpyruvate (PEP) APase and cell wall nonspecific APase. Polyclonal antibodies raised against purified PEP-APase crossreacted specifically with both isozymes. Furthermore, anti-(PEP-APase) IgG detected proteins from a wide range of higher plants, suggesting that the major plant APase isozymes have diverged from a common ancestral form. Quantification on immunoblots indicated that in B. nigra suspension cells experiencing transition from Pi sufficiency to deficiency or vice versa, the amount of total antigenic APase protein correlated closely with total enzyme activity. This was also shown in intact plant roots. Therefore, the activity was governed by the synthesis and degradation of APases. Increases in the amounts of both major APase isozymes occurred simultaneously following Pi deprivation of B. nigra suspension cells, suggesting the involvement of a common regulatory mechanism.

The activation of phosphatase activity of the Ca 2+-ATPase from human red cell membranes by calmodulin, ATP and partial proteolysis

(1) Depending on the assay conditions, the ability of the Ca 2+-ATPase from intact human red cell membranes to catalyze the hydrolysis of p-nitrophenylphosphate is elicited by either calmodulin or ATP. The response of the phosphatase activity to p-nitrophenylphosphate, ATP, Mg 2+ and K + is the same for the activities elicited by ATP or by calmodulin, suggesting that a single process is responsible for both activities. (2) In media with calmodulin, high-affinity activation is followed by high-affinity inhibition of the phosphatase by Ca 2+ so that the activity becomes negligible above 30 μM Ca 2+. Under these conditions, addition of ATP leads to a large decrease in the apparent affinity for inhibition by Ca 2+. (3) In membranes submitted to partial proteolysis with trypsin, neither calmodulin nor Ca 2+ are needed and phosphatase activity is maximal in media without Ca 2+. This is the first report of an activity sustained by the Ca 2+-ATPase of red cell membranes in the absence of Ca 2+. Under these conditions, however, ATP still protects against high-affinity inhibition by Ca 2+. These results strongly suggest that during activation by calmodulin, Ca 2+ is needed only to form the calmodulin-Ca 2+ complex which is the effective cofactor. (4) Protection by ATP of the inhibitory effects of Ca 2+ and the induction of phosphatase activity by ATP + Ca 2+ suggests that activation of the phosphatase by Ca 2+ in media with ATP requires the combination of the cation at sites in the ATPase. (5) Results can be rationalized assuming that E 2, the conformer of the Ca 2+-ATPase, is endowed with phosphatase activity. Under this assumption, either the calmodulin-Ca 2+ complex or partial proteolysis would elicit phosphatase activity by displacing the equilibrium between E 1 and E 2 towards E 2. On the other hand, ATP + Ca 2+ would elicit the activity by establishing through a phosphorylation-dephosphorylation cycle a steady-state in which E 2 predominates over other conformers of the ATPase.

Induction of rat hepatic and intestinal alkaline phosphatase activity produced by bile from bile duct-ligated animals.

Bile duct ligation caused a threefold elevation of not only hepatic but also intestinal alkaline phosphatase. The increase was transient in intestinal mucosa and peaked at 12 h. Hepatic phosphatase levels reached a plateau by 36 h. Intraperitoneal injection of bile from ligated animals into normal rats produced qualitatively similar results. Studies were performed to further characterize the induction of phosphatase activity in both tissues. The addition of bile from ligated animals to organ explants of liver and intestine produced a two- and threefold rise in activity, respectively. Therefore, neural and hormonal factors are not essential in producing this induction. The increased activity produced in vitro in both tissues was due to heat-stable and dialyzable factor(s) and was blocked by inhibitors of protein synthesis. In the intestine activity occurred over the entire brush border as demonstrated by electron microscopic histochemistry. In the liver, increased activity was noted over the entire plasma membrane and was not localized to the canalicular membrane. Tunicamycin treatment of liver and intestinal explants markedly suppressed the induced phosphatase activity. Simultaneous treatment with protease inhibitors restored some of the phosphatase activity. These findings suggest that glycosylation of the alkaline phosphatase might provide at least partial protection from proteolysis.

Alkaline Phosphatase Activity Induction in Human Spleen Sinuses in Storage Diseases.

Human splenic sinuses were observed for the induction of alkaline phosphatase (AP) activity in mucopolysaccharidoses of type I and II, in GM1 gangliosidosis, and in Niemann-Pick's disease, type A. A substantially lower degree of activity was found in Sanfillipo's disease, type A, and in hemosiderin pigmentation of the sinuses. In a number of hematological affections and in control spleens AP activity could not be proved by histochemical means. From the formal pathogenetic view, enzyme activity induction is probably related to lysosomal deposition of the material stored.

The induction of phosphatase activity in thin slices of Jerusalem artichoke tissue by treatment with indole acetic acid

Prolonged washing of thin slices of Jerusalem artichoke (Helianthus tuberosus) did not result in any apparent increase in the activity of the phosphatase enzymes, although the washing process is known to stimulate the activity of many other enzymes. However, treatment of the tissue in either 3×10(-5)M 2,4-dichlorophenoxyacetic acid or 10(-4)M indole acetic acid resulted in a 3-fold increase in the phosphatase activity. Significant stimulations of activity were detectable one hour after placing the tissue in the auxin. Treatment of the tissue in either kinetin or gibberellic acid failed to stimulate the activity of the enzyme. The enhancement of phosphatase activity caused by auxins could not be prevented by adding cycloheximide to the treatment solution an it is concluded that the stimulation occurred as the result of the activation of enzyme already present in the tissue rather than by the de novo synthesis of new enzyme protein.

CYTOCHEMICAL LOCALIZATION OF ACID PHOSPHATASES IN EUGLENA GRACILIS.

The localization of induced and constitutive acid phosphatase activity in Euglena was studied by light and electron microscopy, using two different cytochemical methods. Cells grown in high phosphate medium have constitutive acid phosphatase activity in three regions: in the Golgi complex, around the paramylum bodies, and in the peri-reservoir vesicles. Cells that have formed an induced acid phosphatase by exposure to a phosphate-deficient medium have, in addition to the constitutive activity localized exactly as in the uninduced cell, a strong activity in the pellicle. The induced activity is not uniformly distributed over the pellicle, but is localized at the notch of each pellicle complex, near a group of about four fibrils and near a characteristic vesicle of the endoplasmic reticulum. In the cytostome, where fission begins during division, there is an alternation of large and small pellicle complexes, both of which have induced phosphatase activity. A similar alternation is seen over the entire pellicle of dividing cells.