M6P/IGF2R modulates the invasiveness of liver cells via its capacity to bind mannose 6-phosphate residues.

BACKGROUND & AIMS: The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R), a multifunctional protein, plays a central role in intracellular targeting of lysosomal enzymes and control of insulin-like growth factor II (IGF-II) bioactivity. Importantly, the gene encoding this receptor is frequently inactivated in a wide range of malignant tumors including hepatocellular carcinomas. Thus, M6P/IGF2R is considered a putative liver tumor suppressor. The aim of this study was to establish the impact of the receptor on the invasive properties of liver cells. METHODS: Reconstitution experiments were performed by expression of wild type and mutant M6P/IGF2R in receptor-deficient FRL14 fetal rat liver cells. RNA interference was used to induce M6P/IGF2R downregulation in receptor-positive MIM-1-4 mouse hepatocytes. RESULTS: We show that the M6P/IGF2R status exerts a strong impact on the invasiveness of tumorigenic rodent liver cells. M6P/IGF2R-deficient fetal rat liver cells hypersecrete lysosomal cathepsins and penetrate extracellular matrix barriers in a cathepsin-dependent manner. Forced expression of M6P/IGF2R restores intracellular transport of cathepsins to lysosomes and concomitantly reduces the tumorigenicity and invasive potential of these cells. Conversely, M6P/IGF2R knock-down in receptor-positive mouse hepatocytes causes increased cathepsin secretion as well as enhanced cell motility and invasiveness. We also demonstrate that functional M6P-binding sites are important for the anti-invasive properties of M6P/IGF2R, whereas the capacity to bind IGF-II is dispensable for the anti-invasive activity of the receptor in liver cells. CONCLUSIONS: M6P/IGF2R restricts liver cell invasion by preventing the pericellular action of M6P-modified proteins.

Exploding a myth: the capsule dehiscence mechanism and the function of pseudostomata in Sphagnum.

The nineteenth century air-gun explanation for explosive spore discharge in Sphagnum has never been tested experimentally. Similarly, the function of the numerous stomata ubiquitous in the capsule walls has never been investigated. Both intact and pricked Sphagnum capsules, that were allowed to dry out, all dehisced over an 8-12 h period during which time the stomatal guard cells gradually collapsed and their potassium content, measured by X-ray microanalysis in a cryoscanning electron microscope, gradually increased. By contrast, guard cell potassium fell in water-stressed Arabidopsis. The pricking experiments demonstrate that the air-gun notion for explosive spore discharge in Sphagnum is inaccurate; differential shrinkage of the capsule walls causes popping off the rigid operculum. The absence of evidence for a potassium-regulating mechanism in the stomatal guard cells and their gradual collapse before spore discharge indicates that their sole role is facilitation of sporophyte desiccation that ultimately leads to capsule dehiscence. Our novel functional data on Sphagnum, when considered in relation to bryophyte phylogeny, suggest the possibility that stomata first appeared in land plants as structures that facilitated sporophyte drying out before spore discharge and only subsequently acquired their role in the regulation of gaseous exchange.

Neuron cells uptake of polymeric microcapsules and subsequent intracellular release.

Neuron cells uptake of biodegradable and synthetic polymeric microcapsules functionalized with aggregates of gold nanoparticles incorporated into their shells is demonstrated in situ. In addition to traditionally used optical microscopy, electron microscopy is used both for higher-resolution imaging and for confirming the uptake by focused ion beam cross-sectioning of specific cells in situ. Subsequently, physical methods of release are compared to chemical methods wherein laser-induced intracellular release of dextran molecules into the cytosol of hippocampal neuron cells is studied in comparison to biodegradation. Implications of this work for neuroscience, bio-medicine and single cell studies are discussed.