Mannose 6-phosphate/insulin like growth factor II receptor: the two types of ligands bind simultaneously to one receptor at different sites

Pentamannose 6-phosphate/trilysine substituted aprotinin (PMP-lys-aprotinin) and insulin like growth factor II (IGF II) were used as affinity ligands for the mannose 6-phosphate (M6P) and IGF II binding sites of the M6P/IGF II receptor. Both ligands were cross linked to intact receptor and tryptic fragments of the receptor. The pattern of receptor fragments with M6P and IGF II binding sites differed indicating that the two binding sites are located on different segments of the receptor. The receptor was incubated with [125I]IGF II and pentamannose 6-phosphate substituted bovine serum albumin (PMP-BSA). From these mixtures [125I]IGF II receptor complexes could be precipitated with antibodies against the PMP-BSA indicating that the M6P/IGF II receptor can bind simultaneously IGF II and M6P-containing ligands.     

Mannose 6-phosphate/insulin-like growth factor II-binding proteins in human serum and urine. Their relation to the mannose 6-phosphate/insulin-like growth factor II receptor.

Human serum and urine contain polypeptides which bind mannose 6-phosphate (M6P) and insulin-like growth factor II (IGF II) and crossreact with antibodies against the M6P/IGF II receptor. These polypeptides are considered to be fragments of the M6P/IGF II receptor. The major Mr approx. 205,000 fragment in serum and urine is about 10 kDa smaller in size than the membrane-associated receptor and is accompanied by minor forms with Mr values ranging from 104,000 to 180,000. The presence of receptor fragments in biological fluids indicates that shedding is one of the mechanisms contributing to the turnover of the M6P/IGF II receptor and that receptor fragments are part of the heterogenous group of serum proteins whic bind IGF II.     

Book Reviews

Books reviewed in this article:
W orld F ederation for C ulture C ollections T eaching V ideo (1986).
A C olour A tlas of M icrobiology (1986). R. J. Olds.
A C olour A tlas of I nfectious D iseases 2nd edition (1987). R. T. D. Emond & H. A. K. Rowland.
D iagnostic P icture T ests in I nfectious D iseases (1987). R. T. D. Emond & H. A. K. Rowland
T he A ntimicrobial A gents A nnual (1987). Edited by P. K. Peterson & J. Verhoef.
T he B acteria. Volume 10. T he B iology of Pseudomonas (1986). Edited by J. R. Sokatch.
T he I nfluence of A ntibiotics on the H ost -P arasite R elationship II (1985). Edited by D. Adam, H. Hahn & W. Opperkuch.     

Role of protein phosphatases in insulin-like growth factor II (IGF II)-stimulated mannose 6-phosphate/IGF II receptor redistribution.

The regulated expression of mannose 6-phosphate/insulin-like growth factor II (M6P/IGF II) receptors in plasma membranes has previously been shown to be accompanied by marked changes in the phosphorylation state of the receptors (Corvera, S., Folander, K., Clairmont, K. B., and Czech, M. P. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 7567-7571). In the present study we show that protein phosphatase 2A dephosphorylates the human M6P/IGF II receptor in vitro. Incubation of human fibroblasts with okadaic acid, a specific inhibitor of this phosphatase, resulted in a depletion of M6P/IGF II receptors at the cell surface without affecting their internalization kinetics. The phosphorylation state of the remaining cell surface receptors was 3-fold increased. Thus, the endocytosis rate of M6P/IGF II receptors appears to be unaltered by increased phosphorylation. While the decreased cell surface expression of receptors was reversible upon removal of okadaic acid the IGF II-induced redistribution of M6P/IGF II receptors to the plasma membrane (Braulke, T., Tippmer, S., Neher, E., and von Figura, K. (1989) EMBO J. 8, 681-686) was irreversibly inhibited by the phosphatase inhibitor. Receptor redistribution in response to protein kinase C activation was not affected by okadaic acid. These results suggest that the cell surface expression of M6P/IGF II receptor can be regulated by phosphatase-dependent and -independent pathways. In addition, the phosphorylation state and the steady-state cell surface number of transferrin receptors were not affected by okadaic acid, whereas it impaired the IGF II-stimulated receptor redistribution similarly as for M6P/IGF II receptors. The data indicate that okadaic acid-sensitive protein phosphatases may play a general role in terms of IGF II-modulated receptor recycling.     

Books

Book reviews in this article:
H andbook of M arine M ammals . V olume 3: T he S irenians and B aleen W hales . S. H. Ridgway and R. Harrison (eds.).
L es P hoques M oines -M onk S eal . Ronald and R. Duguy (eds.).
T he E lements of G raphing D ata . W. S. Cleveland.
G uia P ara el R econocimiento de C etaceos del M ar A rgentino . A. Lichter and A. Hooper.
M amiferos M arinos de C hile . W. Sielfeld K.
T he W hale W atcher's H andbook . E. Hoyt. Illustrations by P. Folkens.
W hales and D olphins of N ew Z ealand and A ustralia : A n I dentification G uide . A. N. Baker.     

Insulin-like growth factor II overexpression does not affect sorting of lysosomal enzymes in NIH-3T3 cells.

The sorting of newly synthesized mannose 6-phosphate (M6P)-containing proteins and of the major excreted protein (MEP), a lysosomal thiol proteinase, was studied in NIH-3T3 cells transfected with the cDNA of human insulin-like growth factor II (IGF II) or with the vector alone. Extracts from media and cells labelled with [35S] methionine were used for chromatography on a M6P/IGF II receptor affinity matrix or for immunoprecipitation to assess the distribution of newly synthesized M6P-containing proteins and MEP, respectively. The results indicate that the overexpression of IGF II did not affect the synthesis and the sorting of M6P-containing proteins and of MEP. The binding and uptake of the lysosomal enzyme arylsulfatase A were not affected in IGF II overexpressing cells.     

Regulation of calcineurin by phosphorylation. Identification of the regulatory site phosphorylated by Ca2+/calmodulin-dependent protein kinase II and protein kinase C

The site in calcineurin, the Ca2+/calmodulin (CaM)-dependent protein phosphatase, which is phosphorylated by Ca2+/CaM-dependent protein kinase II (CaM-kinase II) has been identified. Analyses of 32P release from tryptic and cyanogen bromide peptides derived from [32P]calcineurin plus direct sequence determination established the site as -Arg-Val-Phe-Ser(PO4)-Val-Leu-Arg-, which conformed to the consensus phosphorylation sequence for CaM-kinase II (Arg-X-X-Ser/Thr-). This phosphorylation site is located at the C-terminal boundary of the putative CaM-binding domain in calcinerin (Kincaid, R. L., Nightingale, M. S., and Martin, B. M. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 8983-8987), thereby accounting for the observed inhibition of this phosphorylation when Ca2+/CaM is bound to calcineurin. Since the phosphorylation site sequence also contains elements of the specificity determinants for Ca2+/phospholipid-dependent protein kinase (protein kinase C) (basic residues both N-terminal and C-terminal to Ser/Thr), we tested calcineurin as a substrate for protein kinase C. Protein kinase C catalyzed rapid stoichiometric phosphorylation, and the characteristics of the reaction were the same as with CaM-kinase II: 1) the phosphorylation was blocked by binding of Ca2+/CaM to calcineurin; 2) phosphorylation partially inactivated calcineurin by increasing the Km (from 9.9 +/- 1.1 to 17.5 +/- 1.1 microM 32P-labeled myosin light chain); and 3) [32P]calcineurin exhibited very slow autodephosphorylation but was rapidly dephosphorylated by protein phosphatase IIA. Tryptic and thermolytic 32P-peptide mapping and sequential phosphoamino acid sequence analysis confirmed that protein kinase C and CaM-kinase II phosphorylated the same site.     

Angiotensin II interacts with prostaglandin F2alpha and endothelin-1 as a local luteolytic factor in the bovine corpus luteum in vitro

Recent findings suggest that the ovarian renin-angiotensin system may regulate ovarian function through the paracrine/autocrine actions of angiotensin II (Ang II). In this study, we have examined and characterized the local effects of Ang II as a luteolytic factor and its interaction with prostaglandin F2alpha (PGF2alpha) and endothelin-1 (ET-1) in the bovine corpus luteum (CL) of the mid-luteal phase, by using an in vitro microdialysis system (MDS). Ang II was detected in the MDS perfusate (4 pg/ml), and infusion of PGF2alpha (10(-6) M) for 2 h increased the Ang II release by 50-100% during the following experimental period, in addition to its stimulation of ET-1 release. Two 2-h infusions of Ang II (10(-7)-10(-5) M) separated by a 2-h interval induced a dose- and time-dependent decrease of progesterone (P4) release by 41-66%. When the luteal explants were pre-perfused with PGF2alpha (10(-6) M) for 2 h, two consecutive perfusions of Ang II (10(-6) M) at a 2-h interval rapidly reduced the P4 release (by 50%). This reduction occurred 6 h earlier than those of infusions of PGF2alpha or Ang II alone. The simultaneous infusion of either 1) Ang II (10(-6) M) with PGF2alpha (10(-6) M), 2) ET-1 (10(-7) M) with PGF2alpha, or 3) Ang II + ET-1 with PGF2alpha (10(-6) M) for 2 h also induced a rapid and pronounced (60%) decrease in P4 release. Perfusion with the Ang II antagonist blocked the P4-suppressing activity of Ang II alone or PGF2alpha + Ang II infusion. Ang II stimulated the release of ET-1 and oxytocin during infusion but inhibited them after infusion. These results show that Ang II is released in the bovine midcycle CL in vitro, and this peptide, either alone or together with PGF2alpha, can suppress the release of P4. As PGF2alpha directly stimulated Ang II release, Ang II may influence the critical period for starting the cascade of functional luteolysis in vivo and might lead to structural luteolysis with ET-1 as a major vasoconstrictor. The overall results suggest that Ang II may have an important role at luteolysis in the bovine CL.     

Mannose-6-phosphate/Insulin-like Growth Factor II Receptor Expression and Tumor Development

The mannose-6-phosphate/insulin-like growth factor II receptor (M6P/IGF-IIR) is a multi-functional transmembrane glycoprotein whose major function is to bind and transport M6P-bearing glycoproteins from the trans-Golgi network or the cell surface to lysosomes. The cell surface M6P/IGF-IIR also bind and internalizes the insulin-like growth factor II. The receptor gene is considered a « candidate » tumor suppressor gene. The phenotypic consequences of loss of M6P/IGF-IIR through somatic mutation are potentially very complex since M6P/IGF-IIR has a number of roles in cellular physiology. Loss of function mutations in M6P/IGF-IIR gene could contribute to multi-step carcinogenesis. In the light of the multi-functional cellular potential roles of the M6P/IGF-IIR the purpose of this review is to highlight some recent data concerning its normal functions and the potential role of its loss in tumor pathophysiology with the aim to try to clarify the possible underlying mechanisms of its involvement in tumor development.     

Peroxynitrite and the regulation of Na(+),K(+)-ATPase activity by angiotensin II in the rat proximal tubule.

NO reacts spontaneously with superoxide to produce the potent oxidant peroxynitrite. Studies were designed to examine the role of NO-derived oxidants and peroxynitrite on the regulation of Na(+),K(+)-ATPase activity by angiotensin II (ANG II) freshly isolated rat proximal tubules. At picomolar concentrations ANG II stimulates Na(+),K(+)-ATPase activity, but at nanomolar concentrations stimulation is lost. Superoxide dismutase (SOD) was used to examine the role of superoxide and deferoxamine (DFO) and uric acid (UA) were used to examine the role of peroxynitrite. SOD (200 U/mL, 5-min preincubation) restored the stimulatory effect of ANG II (1.31 +/- 0.08-fold; n = 4; P < 0.05 compared to 10(-7) M alone), suggesting a role for superoxide. DFO (100 microm, 5-min preincubation) also restored the stimulatory effect of ANG II (1.40 +/- 0.08-fold; n = 4; P < 0.05, compared to 10(-7) M alone), as did UA (1.22 +/- 0.07-fold; n = 5; P < 0.05, compared to 10(-7) M alone). The NO synthesis inhibitor, N-monomethyl-L-arginine (L-NMMA, 2 mM; 5-min preincubation), also unmasked a stimulatory effect of ANG II at 10(-7) M (1.4 +/- 0.1-fold; n = 7; P < 0.05, compared to 10(-7) M alone). The generation of peroxynitrite was further evidenced by the formation of 3-nitrotyrosine (3-NT). 3-NT increased 3.5-fold in tubules exposed to ANG II (10(-7) M) (0.0054 +/- 0.0019 3-NT/100 tyrosines for control and 0.019 +/- 0.0058 3-NT/100 tyrosines for ANG II, P < .05; n = 4) and L-NMMA prevented the increase. These data suggest that peroxynitrite signaling participates in the regulation of renal of Na(+),K(+)-ATPase activity.     

REVIEWS

O n the N orthwest : C ommercial W haling in the P acific N orthwest 1790–1967. Robert Lloyd Webb.
T he S ei W hale : P opulation B iology , E cology and M anagement . Joseph Horwood
W ildlife R adio T agging , E quipment , F ield T echniques and D ata A nalysis . Robert Hayward.
B iology of the G enus C ephalorhynchus . R. L. Brownell, Jr. and G. P. Donovan, eds.
H andbook of M arine M ammals . V olume 4: R iver D olphins and the L arger T oothed W hales . S. H. Ridgway and R. Harrison, eds.
P olar B ears . Ian Stirling.
T he W hales of H awaii . Kenneth C. Balcomb, III.
W hales , D olphins and P orpoises . Richard Harrison and M. M. Bryden, eds.     

Dominant-negative effect of truncated mannose 6-phosphate/insulin-like growth factor II receptor species in cancer

Oligomerization of the mannose 6-phosphate/insulin-like growth factor?II receptor (M6P/IGF2R) is important for optimal ligand binding and internalization. M6P/IGF2R is a tumor suppressor gene that exhibits loss of heterozygosity and is mutated in several cancers. We tested the potential dominant-negative effects of two cancer-associated mutations that truncate M6P/IGF2R in ectodomain repeats 9 and 14. Our hypothesis was that co-expression of the truncated receptors with the wild-type/endogenous full-length M6P/IGF2R would interfere with M6P/IGF2R function by heterodimer interference. Immunoprecipitation confirmed formation of heterodimeric complexes between full-length M6P/IGF2Rs and the truncated receptors, termed Rep9F and Rep14F. Remarkably, increasing expression of either Rep9F or Rep14F provoked decreased levels of full-length M6P/IGF2Rs in both cell lysates and plasma membranes, indicating a dominant-negative effect on receptor availability. Loss of full-length M6P/IGF2R was not due to increased proteasomal or lysosomal degradation, but instead arose from increased proteolytic cleavage of cell-surface M6P/IGF2Rs, resulting in ectodomain release, by a mechanism that was inhibited by metal ion chelators. These data suggest that M6P/IGF2R truncation mutants may contribute to the cancer phenotype by decreasing the availability of full-length M6P/IGF2Rs to perform tumor-suppressive functions such as binding/internalization of receptor ligands such as insulin-like growth factor II.     

Weight gain of the predator Podisus distinctus (Heteroptera: Pentatomidae) with combinations of the preys Tenebrio molitor (Coleoptera: Tenebrionidae) and Musca domestica (Diptera: Muscidae)

Little is known about Podisus distinctus (Stal) (Heteroptera: Pentatomidae) one of the Asopinae species with good possibilities for mass rearing and releasing against defoliator caterpillars in eucalyptus reforested areas in Brazil. We evaluated the impact of prey combinations on weight of nymphs and adults of P. distinctus. The prey were Musca domestica L. (Diptera: Muscidae) and Tenebrio molitor L. (Coleoptera: Tenebrionidae). The experiment was developed under 25 +/- 0.5 degrees C, 60 +/- 10% R.H. and photophase of 14 hr, with nymphs of P. distinctus individualized in Petri dishes and fed as: T1-larvae of M. domestica during its whole nymphal phase: T2-larvae of M. domestica during its II instar and of T. molitor during the other instars: T3-larvae of M. domestica during II and III instars and of T. molitor during the other instars: T4-larvae of M. domestica during II, III and IV instars and of T. molitor during the V instar; T5- larvae of T. molitor during all instars. P. distinctus presents lower weight when fed with larvae of M. domestica. For this reason it is recommended to feed P. distinctus with T. molitor during its whole nymphal phase or with larvae of M. domestica only during II and III instars and T. molitor during IV and V instars.     

Book reviews

Book reviewed in this article:
T he R umen E cosystem : T he M icrobial M etabolism and its R egulation (1990). Edited by S. Hoshino, R. Onodera, H. Minato & H. Itabashi.
M olecular B iological M ethods for B acillus : M odern M icrobiological M ethods (1990). Edited by C.R. Harwood & S.M. Cutting.
B acillus subtilis : M olecular B iology and I ndustrial A pplication (1989). Edited by B. Maruo & H. Yoshikawa.
M olecular P arasitology (1990). By J.E. Hyde.
F undamental V irology (1990). Second edition. Edited by B.N. Fields, D.M. Knipe, R.M. Chanock, M.S. Hirsch, J.L. Melnick & T.P. Monath.     

Angiotensin II stimulation of the rat pituitary tumoral cell proliferation in vitro.

The effect of angiotensin II (AT II) on proliferation of rat pituitary tumoral cells was investigated in vitro. The tumoral cells were isolated from the prolactin-secreting pituitary tumors induced by stilboestrol implantation. The incorporation of [3H]-thymidine into DNA was used as an index of cell proliferation. It was found that AT II significantly enhanced the [3H]-thymidine incorporation into pituitary tumoral cells in the concentrations of 10(-10) and 10(-8) M. The stimulatory effect disappeared at the concentration of 10(-6) M. The possible involvement of pituitary renin-angiotensin system in pituitary tumorigenesis was discussed.     

Mechanisms of angiotensin II-enhanced connecting tubule glomerular feedback

Increasing Na delivery to the connecting tubule (CNT) causes afferent arteriole (Af-Art) dilation, a process we call CNT glomerular feedback (CTGF). Angiotensin II (ANG II) in the CNT lumen enhances CTGF via PKC. We hypothesized that luminal ANG II stimulates CTGF via activation of protein kinase C (PKC), NADPH oxidase 2 (NOX2), and enhanced production of superoxide (O(2)(-)). Rabbit Af-Arts and adherent CNTs were microdissected and microperfused in vitro. Dilation of the Af-Art was induced by increasing luminal CNT NaCl from 0 to 5, 10, 30, 45, and 80 mM, and the concentration of NaCl that elicited a half-maximal response (EC(50)) was calculated. Compared with vehicle, adding ANG II (10(-9) M) to the CNT lumen reduced EC(50) from 37 ± 3 to 14 ± 1 mM (P < 0.001), indicating ANG II potentiates CTGF. In the presence of ANG II, the O(2)(-) scavenger tempol (10(-4) M) increased EC(50) from 20 ± 4 to 41 ± 3 mM (P < 0.01), the NOX inhibitor apocynin (10(-5) M) increased EC(50) from 17 ± 2 to 39 ± 4 mM (P < 0.01), and the specific NOX2 inhibitor gp91ds-tat (10(-5) M) increased EC(50) from 19 ± 2 to 34 ± 2 mM (P < 0.01). However, tempol, apocynin, and gp91ds-tat had no effect on CTGF in the absence of ANG II. Compared with vehicle, the PKC activator PMA (2 × 10(-7) M) decreased EC(50) from 35 ± 2 to 14 ± 1 (P < 0.001). In the presence of PMA, tempol increased EC(50) from 14 ± 2 to 35 ± 2 mM (P < 0.01). We conclude the PKC/NOX2/O(2)(-) pathway mediates the enhancement of CTGF by luminal ANG II but it does not participate in CTGF in the absence of ANG II.     

Book reviews

Book reviewed in this article:
M icroalgae (1994) By E.W. Becker.
T he E volutionary B iology of V iruses (1994). Edited by S.S. Morse.
MCQ s in M edical M icrobiology and I nfectious D iseases (1993). By P.W. Ross and F.X.S. Emmanuel.
T uberculosis : B ack to T he F uture (1994). Edited by J.D.H. Porter and K.P.W. McAdam.
M aking S afe F ood : A M anagement G uide for M icrobiological Q uality (1991). By W.F. Harrigan and R.W.A. Park.
B acterial P rotein T oxins : FEMS S ymposium No. 73. (1994). Edited by J. Freer, R. Aitken, J.E. Alouf, G. Boulnois, P. Falmagne, F. Fehrenbach, C. Montecucco     

Characterization of the binding of Cu(II) and Zn(II) to transthyretin: effects on amyloid formation

Although metal ions can promote amyloid formation from many proteins, their effects on the formation of amyloid from transthyretin have not been previously studied. We therefore screened the effects of Cu(II), Zn(II), Al(III), and Fe(III) on amyloid formation from wild-type (WT) transthyretin as well as its V30M, L55P, and T119M mutants. Cu(II) and Zn(II) promoted amyloid formation from the L55P mutant of transthyretin at pH 6.5 but had little effect on amyloid formation from the other forms of the protein. Zn(II) promoted L55P amyloid formation at pH 7.4 but Cu(II) inhibited it. Cu(II) gave dose-dependent quenching of the tryptophan fluorescence of transthyretin and the fluorescence of 1-anilino-8-naphthalene sulfonate bound to it. Zn(II) gave dose-dependent quenching of the tryptophan but not the 1-anilino-8-naphthalene sulfonate fluorescence. Apparent dissociation constants for Cu(II) and Zn(II) binding at pH 7.4 of approximately 10 nM and approximately 1 microM (approximately 0.4 microM and approximately 5 microM at pH 6.5), respectively, were obtained from the quenching data. Zn(II) enhanced urea-mediated the dissociation of the L55P but not the WT transthyretin tetramer. Cu(II), depending on its concentration, either had no effect or stabilized the WT tetramer but could enhance urea-mediated dissociation of L55P.     

Polyamines induce aggregation of LHC II and quenching of fluorescence in vitro

Dissipation of excess excitation energy within the light-harvesting complex of Photosystem II (LHC II) is a main process in plants, which is measured as the non-photochemical quenching of chlorophyll fluorescence or qE. We showed in previous works that polyamines stimulate qE in higher plants in vivo and in eukaryotic algae in vitro. In the present contribution we have tested whether polyamines can stimulate quenching in trimeric LHC II and monomeric light-harvesting complex b proteins from higher plants. The tetramine spermine was the most potent quencher and induced aggregation of LHC II trimers, due to its highly cationic character. Two transients are evident at 100μM and 350μM for the fluorescence and absorbance signals of LHC II respectively. On the basis of observations within this work, some links between polyamines and the activation of qE in vivo is discussed.