Effect Of Sodium Orthovanadate Research Articles

Effect of sodium orthovanadate on ovulation isolated ovarian follicles in Siberian Sturgeon (Acipenser baerii) In Vitro

Effects of sodium orthovanadate on oocyte ovulation were examined during in vitro culture of Siberian sturgeon ovarian follicles from hibernating fish. It was shown that sodium orthovanadate stimulates ovulation of Siberian sturgeon oocytes in a dose-dependent manner. The stimulating or inhibitory effect of vanadate depends on the time of addition to the incubation medium. It was also shown that the stimulating effects of orthovanadate depend on the physiological status of hibernating females whose oocytes were isolated

Sodium orthovanadate inhibits growth of acute leukemia HL60 cells and HL60/A cells in vitro

Vanadium is an ultratrace element. The transition metal vanadium, widely exists in the environment and exhibits various biological and physiological effects in the human body, yet with no presently known specific physiological function in mammals. Sodium orthovanadate (SOV) is a kind of vanadium compound. SOV has shown promising antineoplastic activity in several human cancers. But the effects of SOV on acute promyelocytic leukemia (APL) are still unknown. In the present study, for the first time, we found that SOV could inhibit proliferation, induce G2/M cell cycle arrest and apoptosis, and could inhibit autophagy of acute leukemia cell lines in vitro. Thus, our findings suggest that SOV could effectively suppress the growth of acute leukemia HL60 cells and HL60/A cells through the regulations of proliferation, cell cycle, apoptosis and autophagy, and thus may act as a potential therapeutic agent in APL treatment.

Sodium orthovanadate inhibits growth and triggers apoptosis of human anaplastic thyroid carcinoma cells in vitro and in vivo.

Vanadium and its compounds exhibit concentration- and time-dependent anticancer effects on various types of tumor; however, the effects of sodium orthovanadate (SOV) on anaplastic thyroid carcinoma (ATC) have not yet been reported. In the present study, the anticancer effects of SOV on ATC were evaluated. In vitro experiments, including cell viability assays, plate colony formation assays, cell cycle analysis and apoptosis analysis were used to study the role of SOV in ATC. Using in vivo experiments, the effects of SOV on the growth and apoptosis of an ATC-xenograft tumor were studied by comparing the SOV-treatment with the control group. The results revealed that treatment of the human ATC cell line 8505C with SOV inhibited cell viability, induced G2/M phase cell cycle arrest, stimulated apoptosis and reduced mitochondrial membrane potential in a concentration-dependent manner. These findings were confirmed in vivo in a nude mouse ATC xenograft model. In conclusion, the present study demonstrated that SOV inhibited human ATC by regulating proliferation, cell cycle progression and apoptosis, thus suggesting that SOV may be considered a novel option for the treatment of ATC.

Sodium orthovanadate inhibits proliferation and triggers apoptosis in oral squamous cell carcinoma in vitro

Sodium orthovanadate (SOV) is a general inhibitor of tyrosine phosphatases, a large family of enzymes that catalyze the removal of phosphate groups from tyrosine residues. SOV is commonly used in the laboratory to preserve the protein tyrosyl phosphorylation state of proteins under study. It has shown promising antineoplastic activity in some human cancer cell lines; this effect has not been fully investigated in head and neck squamous cell carcinoma. In this study, the effect of SOV on cell growth, proliferation, viability, and apoptosis was assessed in Cal27 cells, an oral squamous cell carcinoma (OSCC) cell line. SOV exhibited dose-dependent inhibition of cell growth and decrease in cell viability and colony formation. The IC50 values for treatment lasting 72 h and 7 days were 25 and 10 µM, respectively. The cytotoxic effect of the drug was associated with poly(ADP-ribose)polymerase cleavage detected by immunoblot. Flow cytometry of Cal27 cells stained with annexinV-FITC and propidium iodide showed a dose-dependent increase in apoptosis that reached approximately 40% at 25 µM SOV. These findings demonstrate that SOV has in vitro antiproliferative and proapoptotic effect on OSCC cells.

Sodium orthovanadate inhibits growth of human hepatocellular carcinoma cells in vitro and in an orthotopic model in vivo

The transition metal vanadium is widely distributed in the environment and exhibits various biological and physiological effects in the human body. As a well known vanadium compound, sodium orthovanadate (SOV) has shown promising antineoplastic activity in several human cancers. However, the effects of SOV on liver cancer are still unknown. In this study, for the first time, we showed that SOV could effectively suppress proliferation, induce G2/M cell cycle arrest and apoptosis, and diminish the mitochondrial membrane potential (MMP) of HCC cells in vitro. In addition, our in vitro results were recapitulated in vivo, showing that SOV exhibited a dose-dependent inhibition of growth of human HCC in an orthotopic model, evidenced by the reduction in tumor size, proliferation index and microvessel density, and increase in cell apoptosis. Most important, we found that SOV could inhibit autophagy in HCC cells in vitro and in vivo, which plays a prodeath role. Thus, our findings suggest that SOV could effectively suppress the growth of human HCC through the regulations of proliferation, cell cycle, apoptosis and autophagy, and thus may act as a potential therapeutic agent in HCC treatment.

642 Potential Protective Effects of Trigonella Foenum Graecum and Sodium Orthovanadate in Hyperglycemia-Induced Alterations in Cardiac Membrane in Alloxan Diabetic Rats

ObjectivesOxidative stress in diabetic tissues is accompanied by high level of free radicals and the simultaneously declined antioxidant enzymes status leading to cell membrane damage. In the present study, the...

The effects of sodium orthovanadate–induced phosphatase inhibition on rat retinal pigment epithelium cell activity

Purpose: The purpose of this study was to assess the contribution of sodium orthovanadate (SOV)-induced phosphatase inhibition to the activation of rat retinal pigment epithelium (RPE) cells.Methods: Confluent cultures of rat RPE cells were treated with the general phosphatase inhibitor SOV. The effects of SOV on the cell cycle were determined by flow cytometry and protein detection of cyclin A and cyclin D1, two different cell cycle regulatory factors. The effects of SOV on cell differentiation were confirmed by immunostaining for α-smooth muscle actin (α-SMA). A migration assay was used to evaluate the effects of SOV on cell migration.Results: SOV could accelerate the cell cycle of RPE cells. Western blotting showed that SOV significantly increased the expression of cyclin A and cyclin D1 in a dose-dependent fashion. The results of α-SMA staining and western blotting demonstrated that SOV induced RPE cells to differentiate toward better contractility and motility. The migration assay indicated that SOV improved the migration activity of RPE cells.Conclusions: Sodium orthovanadate can improve proliferation, differentiation, and migration of rat RPE cells and can also induce the reentry of contact-inhibited rat RPE cells into the cell cycle.

Abstract LB-101: A novel role of semaphorin4a (sema4a) in genotoxin-induced DNA damage response in human lung fibroblasts

Abstract Dysregulation of DNA repair signaling after genotoxin exposure contributes to genomic instability and carcinogenesis. Hexavalent chromium [Cr(VI)] is a genotoxin of occupational and environmental concern. Protein tyrosine phosphatase (PTP) inhibitors (i.e., sodium orthovanadate (SOV)) activate key survival pathways. We reported that SOV enhances clonogenic survival after Cr(VI) exposure by overriding Cr-induced growth arrest in human lung fibroblasts (HLFs). PTP inhibition with SOV increased expression of DNA damage/repair genes as determined by microarray analysis. Kinetic analysis of DNA double-strand breaks (DSBs) by comet assay showed equal DSB formation 15 min after Cr(VI) exposure in the absence and presence of SOV. However, PTP inhibition significantly decreased DSBs 0.5-24 hr after Cr(VI) treatment. Aim of the present study was to determine the molecular mechanism(s) by which PTP inhibition affects DNA damage response during genotoxic stress. Gene expression was examined by DNA Damage Signaling Pathway PCR Array after 1 μM Cr(VI) treatment for 24 hr in the absence or presence of SOV. The PTP inhibitor reversed Cr-mediated changes in expression of several unique genes. Interestingly, the sema4a gene, known to be involved in T cell activation and endothelial cell proliferation and migration, was strongly induced by co-treatment of SOV and Cr(VI). Gene expression correlated with increased sema4a protein expression after co-treatment of SOV and Cr(VI). A potential role of sema4a in Cr-induced DNA DSB formation/repair in the absence or presence of SOV was assessed after sema4a siRNA transfection. Silencing of sema4a did not alter the effect of SOV on Cr-induced DSBs. However, sema4a silencing completely blocked Cr-induced DSBs 4 hr after exposure. These results suggest a novel role of sema4a in DNA DSB formation/repair in normal HLFs. Taken together, these data shed light on the emerging role of semaphorins as mediators of cell survival as well as potential therapeutic targets in carcinogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-101.

Tyrosine phosphorylation pathway is involved in interferon-gamma (IFN-gamma) production; effect of sodium ortho vanadate.

The molecular mechanisms regulating IFN-gamma production have yet to be well characterized. We describe here how treatment of activated cultures of peripheral blood mononuclear cells (PBMC) with the phosphotyrosine phosphatases (PTP) inhibitor sodium ortho vanadate results in greatly enhanced IFN-gamma production. Conversely, cellular proliferation of the same cultures is profoundly inhibited by treatment with vanadate, while the expression of IL-2R and DR molecules on activated lymphocytes remains substantially unmodified. Increased IFN-gamma production, but not inhibition of cellular proliferation, was also observed in mitogen-activated vanadate-treated Jurkat cells. On the other hand, IFN-gamma production induced in cultures of PBMC treated or not with vanadate, was strongly inhibited by incubation with the protein tyrosine kinase (PTK) inhibitor herbimycin A. As a result of the inhibited phosphatase activity, substrates for PTK become hyperphosphorylated on tyrosine residues, as shown by Western blot analysis of cell lysates from cultures of PBMC treated with vanadate. We suggest that the tyrosine phosphorylation pathway plays a role in regulating IFN-gamma production.

Protein tyrosine phosphatases encoded in Cotesia plutellae bracovirus: Sequence analysis, expression profile, and a possible biological role in host immunosuppression

A genome project has been launched and aims to sequence total genome of Cotesia plutellae bracovirus (CpBV). On this process, several putative open reading frames have been proposed, among which there was a large gene family coding for protein tyrosine phosphatases (PTPs). This study analyzed the deduced amino acid sequences of 14 CpBV-PTPs in terms of conserved domains with other known polydnaviral PTPs and determined their expression patterns in diamondback moth, Plutella xylostella, parasitized by C. plutellae. The analyzed CpBV-PTPs share the common 10 motifs with classical type of PTPs. However, there are variations among CpBV-PTPs in active site sequence and phosphorylation sites. Quantitative real-time polymerase chain reaction (PCR) indicated that most PTPs in the parasitized P. xylostella were expressed from the first day of parasitization and increased the expression levels during parasitization. All 14 PTPs were expressed in both immune-associated tissues of fat body and hemocytes in the parasitized host. During last instar, the PTP enzyme activity of the parasitized P. xylostella was significantly lower than that of the nonparasitized. The reduction of the PTP activity was observed in cytosolic fraction, but not in membrane fraction. The hemocytes of parasitized P. xylostella markedly lost their spreading ability in response to a cytokine (PSP1: plasmatocyte-spreading peptide 1). The functional link between the reduced PTP activity and the suppressed hemocytic behavior was evidenced by the inhibitory effect of sodium orthovanadate (a specific PTP inhibitor) on hemocyte-spreading behavior of nonparasitized P. xylostella. These results suggest that CpBV-PTPs are expressed in the parasitized P. xylostella and affect cellular PTP activity, which may be associated with host immunosuppression.

Sodium Orthovanadate Enhances Proliferation of Progenitor Cells in the Adult Rat Subventricular Zone after Focal Cerebral Ischemia

Neuronal progenitor cells able to produce new neuron and glia persist in the adult central nervous system (CNS). Their proliferation is up-regulated by growth factors or cytokines under some pathological conditions, including ischemia. Because sodium orthovanadate (SOV), a protein tyrosine phosphatase inhibitor, can up-regulate tyrosine kinase-linked growth factor receptor signaling via the inhibition of tyrosine residue dephosphorylation, it may be capable of enhancing progenitor cells. To investigate the effect of SOV on progenitor cells in the subventricular zone (SVZ), we injected rats intraperitoneally with 50 mg/kg bromodeoxyuridine (BrdU) and 12.5 or 25 mM SOV or BrdU and saline (control) on days 1 to 7 after middle cerebral artery occlusion. The density of BrdU-positive cells in the ipsilateral SVZ showed a significant SOV dose-dependent increase. This effect was found only in the ipsilateral and not contralateral SVZ, and it was not found in nonischemic rats. Double immunolabeling with BrdU and double cortin, a marker of migrating neuroblast, revealed that the density of double-positive cells increased significantly in an SOV dose-dependent manner. Terminal deoxynucleotidyl transferase dUTP nick-end labeling staining suggested that the SOV-induced increase was not due to antiapoptotic effects. Treatment with SOV also significantly increased the density of cells positive for BrdU and phosphorylated Akt and BrdU and phosphorylated extracellular signal-regulated kinase (ERK). We postulate that ischemia triggers off the proliferation of SVZ cells by bioactive factors such as growth factors and that SOV enhances the proliferation of only triggered-off SVZ cells with Akt and ERK activation. Our findings suggest that SOV may aid in the self-repair of the postischemic CNS.

Facilitation of the Purinergic Contractile Response of the Guinea Pig Vas Deferens by Sodium Orthovanadate

Experiments were carried out to examine the effects of protein tyrosine kinase (PTK) and protein tyrosine phosphatase inhibitors on the purinergic contraction of the guinea pig vas deferens. Sodium orthovanadate (SOV) produced a robust increase of the amplitude of contractions evoked by both neurogenic electrical field stimulation and exogenous ATP. This effect of SOV was concentration- and time-dependent, as well as, reversible and reproducible. Genistein, a PTK inhibitor, but not its inactive structural analog daidzein, inhibited the SOV-induced facilitation of the purinergic contraction. Another PTK inhibitor, 2,5-dihydroxycinnamic acid methyl ester, which is structurally unrelated to genistein, also inhibited the facilitation effects of SOV. Although an application of as low as 3 microM of these inhibitors significantly decreased the effect of SOV, other PTK inhibitors, namely, butein, levandustin C, and thyrphostin 23, were less effective even at concentrations of 100 microM. Western blot experiments showed that the facilitation of the purinergic contraction by SOV is associated with a prominent increase in the level of tyrosine phosphorylation of proteins with estimated molecular sizes of 180 and 123 kDa, which was reversed in the presence of genistein. Evidence is also presented that argue against the possibility that inhibition of the Na(+)/K(+)-ATPase or ATPases, responsible for the clearance of ATP is involved in the SOV-induced facilitation of the purinergic contraction. Together, these results suggest that the responsiveness of the smooth muscle of the vas deferens to the actions of ATP is modulated via a previously unidentified mechanism, which may involve protein tyrosine phosphorylation.

Effect of sodium orthovanadate on glycosylation of the phosphopeptidomannans involved in the cell–cell aggregation of the yeast Kluyveromyces bulgaricus

In studies of yeast flocculation it has been found that low concentrations of vanadium contained in sodium orthovanadate do not affect the growth and the cell–cell adhesion of the yeast Kluyveromyces bulgaricus, whereas high concentrations delay the growth of the yeasts and strongly inhibit flocculation. Moreover, higher sensitivity to Hygromycin B and calcofluor white was taken to imply altered cell wall integrity which is supported by compositional analysis of the extracted phosphopeptidomannans. Yeasts grown on sodium orthovanadate show a decrease in the percentage of phosphopeptidomannans and their compositions. It is proposed that the vanadium contained in sodium orthovanadate has a similar conformation to phosphorus and competes with phosphorus in phosphorylated compounds. The decrease of carbohydrate components and phosphorus linking to phosphopeptidomannans detected may alter their structure and modify ligand binding properties.

Growth factor-stimulated protein synthesis is inhibited by sodium orthovanadate.

The study of intracellular signaling pathways has been aided by the use of sodium orthovanadate, a cell-permeable inhibitor of tyrosine phosphatases. However, long-term addition of sodium orthovanadate is often cytotoxic. In this study we demonstrate that the growth factor-mediated increase in the rate of protein synthesis was inhibited by sodium orthovanadate. This effect of sodium orthovanadate was dose-dependent, with an IC50 of 40 microM and maximal inhibition obtained at 100 microM. As a consequence, the fetal bovine serum-mediated induction of the immediate-early genes, c-Fos and MKP-1, at the protein level was inhibited by orthovanadate. Orthovanadate's ability to attenuate protein synthesis was partially reversible, and was no longer evident when the agent was added 6 h after addition of growth factor to cells. Analysis of several elements of signaling pathways which are known to regulate protein synthesis in a positive manner (p42/p44 MAPK, AKT and p70 S6K stimulation, and hyperphosphorylation of PHAS-I) were not inhibited but rather were stimulated by orthovanadate. Thus, sodium orthovanadate is a potent inhibitor of growth factor-stimulated protein synthesis independent of p42/p44 MAPK or PI3K-p70 S6K activation.

Effect of vanadate on the activity of rat jejunal 6-phosphofructo-1-kinase

The effect of sodium orthovanadate on the activity of 6-phosphofructo-1-kinase (PFK) in the epithelial cells of rat small intestine was investigated. Injection of vanadate (2.5 mg/rat) into rats at 2-day intervals per week for two consecutive weeks resulted in a significant decrease in the maximal activities and activity ratios (activity at 0.5 mM fructose-6-phosphate at pH 7.0/activity at pH 8.0 v 0.5 V ]) of the partially purified PFK in rat jejunum. Also, the sensitivity of jejunal PFK to inhibition by ATP increased in rats treated with vanadate. The addition of 1 μM fructose-2,6-biphosphate and 50 μM AMP in the assays released the enzyme inhibition by ATP, and no significant difference was seen between vanadate-injected and control rats. Moreover, the extent of activation with 1 μM fructose-2,6-bisphosphate was significantly higher (79%) in vanadate-injected rats than in control rats (26%). The present results indicate that rat jejunal PFK is highly inhibited with vanadate in vivo. Therefore, although vanadate has been considered to be an insulin-like agent, because of its insulin-like effects on adipocytes and skeletal muscle, the present results may indicate that this behavior could not be applicable to normal rat tissues, because the effect of vanadate on jejunal PFK is clearly opposite that of insulin.

Vanadate causes synthesis of endothelium-derived NO via pertussis toxin-sensitive G protein in pigs.

The effects of sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, on the endothelial nitric oxide (NO) pathway were studied in vitro. Vanadate caused endothelium-dependent relaxations in isolated porcine coronary arteries, which were abolished by N omega-nitro-L-arginine methyl ester. The relaxations were also abolished by pertussis toxin, an inhibitor of certain G proteins. Tyrosine kinase inhibitors, genistein and alpha-cyano-3-ethoxy-4-hydroxy-5-phenyl-methylcinnamamide (ST-638), significantly attenuated the vanadate-induced relaxations. Vanadate also caused pertussis toxin-sensitive, endothelium-dependent relaxations in isolated porcine renal and femoral arteries and jugular veins. Immunoblots, using an antibody to phosphotyrosines and to c-Src in native porcine aortic endothelial cells, respectively, showed that vanadate induced an elevation of phosphotyrosine proteins and a decrease in the amount of the active form of c-Src family kinases; both changes were markedly suppressed by cotreatment with ST-638. These results indicate that in porcine blood vessels, vanadate causes a synthesis of endothelium-derived NO for which endothelial tyrosine kinases and pertussis toxin-sensitive G protein are considered to be closely involved.

Effect of sodium orthovanadate on the hepatobiliary clearance of rose bengal in streptozotocin-induced diabetic rats

Sodium orthovanadate is known to promote glucose uptake in muscle and adipose tissues and has been suggested as a possible oral hypoglycemic agent. In addition, insulin-dependent diabetes has been shown to alter the hepatobiliary clearance of several drugs in rats. This study has determined whether orthovanadate, like insulin, can reverse diabetes-induced changes in the biliary excretion of endogenous bile acids and in the hepatobiliary clearance of rose bengal. Six groups of male Sprague-Dawley rats were used: normal, insulin-treated normal, vanadate-treated normal, diabetic, insulin-treated diabetic, and vanadate-treated diabetic. Diabetes was induced by injection of streptozotocin (45 mg/kg, i.v.). One week later, insulin (2–4 U/day, s.c.) and sodium orthovanadate (877 ± 82 μmol/kg/day, p.o.) treatments were initiated. After 4 weeks, the clearance and biliary excretion of rose bengal (60 μmol/kg, i.v.) were determined for 3 hr. Bile flow rate, rose bengal excretion, and excretion of endogenous bile acids were unchanged in the two treated normal groups inthe insulin-treated diabetic rats. These parameters were increased in untreated diabetic and vanadate-treated diabetic rats as compared with normal. Pharmacokinetic analyses indicated that total and biliary clearances of rose bengal were increased in diabetic rats and orthovanadate did not reverse these changes. However, liver weight and serum glucose concentrations were reduced by orthovanadate treatment. These data indicate that the oral insulinomimeric chemical sodium orthovanadate effectively reversed some, but not all, of the diabetes-induced alterations of hepatic function.

Effects of vanadate on glycolytic enzymes and malic enzyme in insulin-dependent and -independent tissues of diabetic rats

The effects of sodium orthovanadate (0.6 mg/ml in drinking water) on hexokinase isozymes, pyruvate kinase and malic enzyme in liver and kidney of control and alloxan diabetic rats were studied and compared. Vanadate treatment of diabetic rats normalized hyperglycemia and almost completely restored the differentially altered enzyme profile of liver (a tissue that underutilizes glucose in diabetes) and kidney (a tissue that overutilizes glucose during diabetes). Vanadate therapy, however, could not restore the depressed plasma insulin level of diabetic rats. The study clearly indicates that vanadate can effectively normalize many metabolic abnormalities even at a low insulin level in both insulin-dependent and -independent tissues of diabetic rats.

Sodium orthovanadate induces in vitro ovulation and ovarian prostaglandin synthesis in brook trout (Salvelinus fontinalis)

The in vitro effects of sodium orthovanadate (Na3VO4), a G-protein activator, on ovulation and prostaglandin (PG) synthesis were investigated in the brook trout (Salvelinus fontinalis) ovary. PGE and PGF levels in incubation medium of either extrafollicular (EF) tissue or follicles were measured by specific radioimmunoassays (RIA). PGE levels in follicle incubates were increased by Na3VO4 at both pre-germinal vesicle breakdown (preGVBD) and preovulatory (preOV) stages. However, an increase of PGF levels in follicle incubates was observed only in preGVBD follicles in the presence of Na3VO4. The preOV follicles spontaneously released more PGF than preGVBD follicles and the level was not affected by Na3VO4 treatment. In contrast, in incubates of EF tissue, Na3VO4 induced dosage-dependent increases in PGE and PGF at either stage. The Na3VO4-stimulated increase of PGE in preOV follicle incubates was significantly reduced by the translational inhibitor, cycloheximide (5 μM), but not by the transcriptional inhibitor, actinomycin (5 μM). PGF levels in preOV follicle incubates were also significantly reduced by cycloheximide and actinomycin in controls, but not in the presence of 0.1 mM Na3VO4. The results suggest that protein synthesis was required for Na3VO4 to increase accumulation of PGE, and in maintaining control PGF levels in preOV follicles. In addition, since PGF levels in preOV follicles were not reduced by either inhibitor in the presence of Na3VO4, a Na3VO4-stimulated increase of PGF levels was unmasked that apparently acts through a non-translational pathway. In vitro ovulation was also significantly increased by 0.1 mM Na3VO4. However, the Na3VO4-induced ovulation was not inhibited by either actinomycin or cycloheximide. The data imply that the mechanism(s) by which Na3VO4 induces ovulation are distinct from that for stimulating PG accumulation. When preOV follicles were incubated with 10 μM forskolin, no stimulatory effect on ovulation, or on PGE and PGF levels was observed. The data strongly indicate that the effects of Na3VO4 on ovulation and ovarian PG levels were not mediated by an increase in cAMP.

Effect of vanadate on protein phosphorylation and on acid phosphatase activity in the canine prostate

To evaluate the possible role of intracellular phosphatases in the local regulation of prostatic functions, the effect of sodium orthovanadate (VO 4), an inhibitor of phosphotyrosyl protein phosphatases, was studied on both protein phosphorylation and acid phosphatase activity. Secretory and non-secretory epithelial cells were isolated from normal and metaplastic prostates and incubated with [ 32P]phosphate in the presence and in the absence of VO 4; the phosphoproteins were separated by electrophoresis and the gels were either directly submitted to autoradiography or after an alkali treatment to reveal those proteins enriched in phosphotyrosine. Prior to alkali treatment, several phosphoproteins were evidenced and in less than half of the cell preparations a slight increase in labeling intensity under vanadate (<75%) was observed in two phosphoproteins, p57 and p44. After alkali treatment: (1) the effect of VO 4 on p57 remained in the order of 44–45% and it was restricted to less than half of non-secretory cell preparations; (2) its effect on p44 was intensified (134–207%) and observed in all cell types and in more than 80% of all preparations; and (3) in half of non-secretory cell preparations from metaplastic glands, an effect of VO 4 on p35 (127%) became evident. In all instances, with normal and/or metaplastic prostates, protein phosphorylation activity, either total or alkali-resistant and in the presence or in the absence of VO 4, was always higher in non-secretory epithelial cells as compared to secretory cells. In normal glands, prostatic acid phosphatase (PAP) and phosphotyrosine (p-Tyr) phosphatase activities were elevated and higher in secretory cells compared to non-secretory cells; on the contrary, these activities were very low in secretory and non-secretory cells from metaplastic glands. The acid phosphatase activity on phosphoserine and phosphothreonine was negligible while phosphotyrosine was hydrolysed to the same extent as p-nitrophenyl phosphate in all cell types. The PAP and p-Tyr phosphatase activities were strongly inhibited by VO 4 ( > 85%) in all cell types. Tartrate was a more potent inhibitor of both PAP and p-Tyr phosphatase activities measured with cells from normal glands ( > 80%) as compared to those of cells from metaplastic prostates (35–60%). Thus, vanadate inhibits PAP and p-Tyr phosphatases in prostatic cells and enhances the level of specific phosphoproteins, namely among alkali-resistant phosphoproteins. It is proposed that intracellular phosphatases, and possibly PAP, regulate protein phosphorylation in the prostate and therefore participate in the local modulation of prostatic growth.