An in situ study of beta-glucosidase activity in normal and gaucher fibroblasts with fluorogenic probes

Beta-glucosidase activity was evaluated in situ by means of fluorogenic probes in normal human fibroblasts and fibroblasts from homozygous carriers of the Gaucher trait. Probe internalization, targeting to lysosomes and post-cleavage probe retention were the primary concerns. Internalization and targeting were attempted by in situ photosensitized labilization of lysosomal membranes, lysosomotropic detergents and the use of low density lipid (LDL) or the receptor ligand apolipoprotein E (ApoE). Post-cleavage increase of fluorescence with fluoresceinyl (bis) betaglucopyranoside was appreciably above the rather large pre-cleavage emission. In cells incubated overnight with nonylumbelliferylbetaglucoside (UG9) in the presence of bovine serum albumin and in the absence of ApoE, the probe was dealt with as a cytotoxic agent, accumulating in a paranuclear cap, most likely comprising elements of the endoplasmic reticulum (ER) and Golgi apparatus. Targeting of UG9 to lysosomes occurred within 1 to 3 h of preincubation in the presence of ApoE. There was some evidence of specificity, as Gaucher fibroblasts exhibited weaker cleavage of UG9 (by 50 per cent or more) compared to normal fibroblasts, but in the Gaucher cells there was some residual beta-glucosidase activity. Cleavage of UG9 was nearly totally suppressed in Gaucher cells treated with the beta-glucosidase inhibitor, conduritol B epoxide, for 24 h to 7 days. Suppression in the control fibroblasts was evident but to a lesser degree. The in situ method of fluorogenic assay established for beta-glucosidase deficiency, is in principle applicable to enzyme deficiencies in other lysosomal storage diseases, or to evaluate enhanced enzyme activity following gene therapy.     

The effect of atebrine and an acridine analog (BCMA) on the coenzyme fluorescence spectra of cultured melanoma and Ehrlich ascites (EL2) cells.

Coenzyme fluorescence spectra of single living cells are due to free pyridine nucleotides (folded configuration), bound pyridine nucleotides (unfolded configuration) and a third component, possibly a mixture or flavins. Such spectra can be used to recognize possible differences in coenzyme composition between cell lines or changes of metabolic pathways due to chemicals acting at levels below or above cytotoxicity, by high resolution spectrofluorometry. A study of spectra recorded from cultured Ehrlich ascites (EL2), and Harding Passey melanoma cells (HPM-67 and HPM-73 line) grown under comparable conditions, shows that free NAD(P)H predominates in HPM-67 and EL2, while this coenzyme is bound in HPM-73. The free/bound ratio may be profoundly modifed by chemicals, e.g. in the HPM-73 increase of free and decrease of bound NAD(P)H occurred upon treatment with 10(-6) oligomycin. When atebrine at levels (10(-6) M) below cytotoxicity was added, there was a decrease of the free NAD(P)H spectrum possibly through energy transfer from NAD(P)H to atebrine. Consideration of long range energy transfer i.e., excitation of atebrine by fluorescence of NAD(P)H vs. short range transfer of excitation energy from free NAD(P)H to atebrine, favors the latter mechanism. A transient (reversible) increase in atebrine fluorescence is seen following intracellular microinjection of substrate (e.g. glucose-6-P) leading to an increase in free NAD(P)H. At cytotoxic levels of atebrine (e.g 2 x 10(-5) M) an irreversible increase of atebrine fluorescence is seen. The microspectrofluorometric technique appears therefore well suited to study physiological processes at the level of intracellular coenzymes, as well as possible processes of intermolecular energy transfer in the microenvironment.     

Microspectrofluorometry of fluorescent photoproducts in photosensitized cells. Relationship to cellular quiescence and senescence in culture

Microspectrofluorometry of L and WI-38 cells reveals chemical/structural changes due to quiescence or senescence, i.e., lipid peroxidation, spontaneous or photosensitized by hematoporphyrin. Cells treated with hematoporphyrin and a lysosomal umbelliferone probe show a fast-rising umbelliferone emission, plus a fluorescent photoproduct. Studies in rapidly growing versus quiescent L, early passage/late passage WI-38 cells, suggest accumulation of fluorescence Schiff bases (i.e., their association with granular regions of cells in stationary phase, spectral properties, fast increase in photosensitized cells) and a possible lysosomal membrane permeabilization in quiescent or senescent cells.     

The differential effects of the carcinogen dimethylnitrosamine on isocitrate and 6-phosphogluconate metabolism in single intact cells

A microspectrofluorimetric study is made of the influence of dimethylnitrosamine on NADP reduction, following sequential microinjections into the same L cell, of two substrates: (1) isocitrate, with activity of isocitrate dehydrogenase both in the extramitochondrial and intramitochondrial compartments, (2) 6-phosphogluconate, with activity of the dehydrogenase in the extramitochondrial compartment. In control L cells a two-step reduction of NAD(P) is obtained followed by relatively slow reoxidation. In the minutes which follow addition of carcinogen, e.g., dimethylnitrosamine, to the cell medium the isocitrate and 6-phosphogluconate-induced transient NADP reoxidation is decreased in magnitude compared to control, while the rate constant of NADPH reoxidation is considerably accelerated, possibly due to requirements at the level of the microsomal metabolizing system. Observations within the first hour of carcinogen addition suggest an interesting system for evaluating the immediate actions of carcinogens at extranuclear sites: i.e., a comparative study of NADP reduction-reoxidation rate constants via injection of substrates for extra- vs. intramitochondrial pathways.     

An InCytes from MBC Selection: Importin β Regulates the Seeding of Chromatin with Initiation Sites for Nuclear Pore Assembly

The nuclear envelope of higher eukaryotic cells reforms at the exit from mitosis, in concert with the assembly of nuclear pore complexes (NPCs). The first step in postmitotic NPC assembly involves the “seeding” of chromatin with ELYS and the Nup107-160 complex. Subsequent steps in the assembly process are poorly understood and different mechanistic models have been proposed to explain the formation of the full supramolecular structure. Here, we show that the initial step of chromatin seeding is negatively regulated by importin β. Direct imaging of the chromatin attachment sites reveals single sites situated predominantly on the highest substructures of chromatin surface and lacking any sign of annular structures or oligomerized pre-NPCs. Surprisingly, the inhibition by importin β is only partially reversed by RanGTP. Importin β forms a high-molecular-weight complex with both ELYS and the Nup107-160 complex in cytosol. We suggest that initiation sites for NPC assembly contain single copies of chromatin-bound ELYS/Nup107-160 and that the lateral oligomerization of these subunits depends on the recruitment of membrane components. We predict that additional regulators, besides importin β and Ran, may be involved in coordinating the initial seeding of chromatin with subsequent steps in the NPC assembly pathway.     

Antimicrobial benzodiazepine‐based short cationic peptidomimetics

Antimicrobial peptides (AMPs) appear to be good candidates for the development of new antibiotic drugs. We describe here the synthesis of peptidomimetic compounds that are based on a benzodiazepine scaffold flanked with positively charged and hydrophobic amino acids. These compounds mimic the essential properties of cationic AMPs. The new design possesses the benzodiazepine scaffold that is comprised of two glycine amino acids and which confers flexibility and aromatic hydrophobic ‘back’, and two arms used for further synthesis on solid phase for incorporation of charged and hydrophobic amino acids. This approach allowed us a better understanding of the influence of these features on the antimicrobial activity and selectivity. A novel compound was discovered which has MICs of 12.5 µg/ml against Staphylococcus aureus and 25 µg/ml against Escherichia coli, similar to the well‐known antimicrobial peptide MSI‐78. In contrast to MSI‐78, the above mentioned compound has lower lytic effect against mammalian red blood cells. These peptidomimetic compounds will pave the way for future design of potent synthetic mimics of AMPs for therapeutic and biomedical applications. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.