The tumour suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) shares homology with protein tyrosine phosphatases (PTPases). Similarly, bis-peroxovanadium (bpV) molecules that are well-established PTPase inhibitors were shown to inhibit PTEN, but at up to 100-fold lower concentrations. The preference and potency of the bpVs towards PTEN was validated in vivo as demonstrated by: (i) an increase of Ser473 phosphorylation of protein kinase B (PKB) at similar low nanomolar doses, (ii) the lack of any effect on the PKB phosphorylation in the PTEN negative cell line UM-UC-3, (iii) the ability to rescue Ly294002-induced phosphoinositide 3-kinase inhibition and (iv) a lack of tyrosine phosphorylation at low nanomolar doses.

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Plasma membrane isolated from rat sperm cells after incubation in vitro had a significantly lower cholesterol/phospholipid mole ratio when the medium contained serum albumin. Transfer of albumin-bound phospholipids to the membrane can largely account for this effect. The result is broadly consistent with a previously proposed model for albumin-induced destabilization of sperm membrane (capacitation) and its reversal by seminal plasma membrane vesicles. Albumin also decreased sialic acid and, more specifically, ganglioside levels, presumably by promoting release of sperm neuraminidase. Cholesteryl ester comprised up to 0.5 mol/mol of cholesterol in these plasma mem rane preparations. Mammalian sperm cells can express fertilizing capacity after incubation in vitro for an interval of usually a few hours in a chemically defined medium containing serum albumin (1-6). Although the molecular changes underlying transformation to a capacitated state are unclear, albumin specifically facilitates this process (4). Substantial changes in sperm plasma membrane proteins accompany incubation with albumin (7); however, they seem to involve proteolysis after the acrosome reaction. A clue that lipid binding by albumin might be involved in its ability to promote capacitation was provided by the observation that presaturation of the protein with cholesterolt abolished this capability (4). In view of this finding and the discovery that cholesterol-bearing decapitation factor (DF) vesicles from seminal plasma and synthetic vesicles containing the sterol block capacitation in rabbit and rat spermatozoa (8-12), changes in the lipid bilayer of the sperm plasma membrane seem to be necessary for expression of fertilizing capacity.One interpretation of these observations is that albumin decreases the cholesterol/phospholipid (Chol/PL) ratio in the sperm plasma membrane (13). Spectroscopic data reveal that cholesterol restricts the thermal motion of fatty acid chains in a phospholipid bilayer above the gel-to-liquid transition temperature (14-16), and this causes a "condensation effect" and decreases permeability (17). An increase in bilayer microviscosity evidently accounts for the inhibit'ry effect of cholesterol on fusion between plasma membranes of cultured muscle cells (18) and synthetic phospholipid membranes (19). Decreasing the Chol/PL ratio in sperm plasma mqmbrane, therefore, may be anticipated to promote fusion with the outer acrosomal membrane; this intracellular fusion occurring in the acrosome reaction is a precondition for mammalian fertilization (20). A vesicle-induced reversal of this putative change in the plasma membrane Chol/PL ratio might account for the ability of these vesicles to inhibit spermatozoan fertilizing capacity reversibly (11,12).To test this idea, plasma membrane preparations isolated from rat spermatozoa after incubation in vitro were partially characterized with respect to their lipid composition. It was anticipated bovine serum albumin would decrease the Chol/PL ratio in sperm plasma membrane i...

The functions and morphology of cellular membranes are intimately related and depend not only on their protein content but also on the repertoire of lipids that comprise them. In the absence of in vivo data on lipid asymmetry in endomembranes, it has been argued that motors, scaffolding proteins or integral membrane proteins rather than non-lamellar bilayer lipids such as diacylglycerol (DAG), are responsible for shaping of organelles, local membrane curvature and fusion. The effects of direct alteration of levels of such lipids remain predominantly uninvestigated. Diacylglycerol (DAG) is a well documented second messenger. Here we demonstrate two additional conserved functions of DAG: a structural role in organelle morphology, and a role in localised extreme membrane curvature required for fusion for which proteins alone are insufficient. Acute and inducible DAG depletion results in failure of the nuclear envelope (NE) to reform at mitosis and reorganisation of the ER into multi-lamellar sheets as revealed by correlative light and electron microscopy and 3D reconstructions. Remarkably, depleted cells divide without a complete NE, and unless rescued by 1,2 or 1,3 DAG soon die. Attenuation of DAG levels by enzyme microinjection into echinoderm eggs and embryos also results in alterations of ER morphology and nuclear membrane fusion. Our findings demonstrate that DAG is an in vivo modulator of organelle morphology in mammalian and echinoderm cells, indicating a fundamental role conserved across the deuterostome superphylum.

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