Polarized expression of integrin receptors (alpha 6 beta 4, alpha 2 beta 1, alpha 3 beta 1, and alpha v beta 5) and their relationship with the cytoskeleton and basement membrane matrix in cultured human keratinocytes

In human keratinocytes cultured in conditions which allow differentiation and stratification and are suitable to reconstitute a fully functional epidermis, alpha 6 beta 4 and two members of the beta 1 integrin family (alpha 2 beta 1 and alpha 3 beta 1) were respectively polarized to the basal and lateral domains of the plasmamembrane both in growing colonies and in the reconstituted epidermis. Conversely, the alpha v integrin subunit, presumably in association with beta 5, was expressed at the basal surface in growing and migrating but not in stationary keratinocytes. The integrin alpha 6 beta 4: (a) was organized in typical patches which often showed a "leopard skin" pattern where spots corresponded to microfilament-free areas; (b) was not associated with focal contacts containing vinculin and talin but rather corresponded to relatively removed contact areas of the basal membrane as shown by interference reflection microscopy; and (c) was coherent to patches of laminin secreted and deposited underneath the ventral membrane of individual cells. The two beta 1 integrins (alpha 2 beta 1 and alpha 3 beta 1), both endowed with laminin receptor properties, were not associated with focal adhesions under experimental conditions allowing full epidermal maturation but matched the lateral position of vinculin (but not talin), cingulin, and desmoplakin, all makers of intercellular junctions. Often thin strips of laminin were observed in between the lateral aspects of individual basal keratinocytes. The integrin complex alpha v beta 5 had a topography similar to that of talin- and vinculin-containing focal adhesions mostly in the peripheral cells of expanding keratinocyte colonies and in coincidence with fibronectin strands. The discrete topography of beta 1 and beta 4 integrins has a functional role in the maintenance of the state of aggregation of cultured keratinocytes since lateral aggregation was impaired by antibodies to beta 1 whereas antibodies to beta 4 prevented cell-matrix adhesion (De Luca, M., R. N. Tamura, S. Kajiji, S. Bondanza, P. Rossino, R. Cancedda, P. C. Marchisio, and V. Quaranta. Proc. Natl. Acad. Sci. USA. 87:6888-6892). Moreover, the surface polarization of integrins followed attachment and depended both on the presence of Ca2+ in the medium and on the integrity of the cytoskeleton. We conclude that our in vitro functional tests and structural data suggest a correlation between the pattern of integrin expression on defined plasmamembrane domains and the mechanism of epidermal assembly.     

The effect of feeding on plasma immunoreactive ACTH and beta-endorphin levels in newborn infant.

In order to clarify whether an interaction between endogenous opioids and feeding occurs at birth, we studied Beta-endorphin (beta-EP) and ACTH plasma levels in response to a feed of 10% glucose, or formula, in 120 healthy full-term infants. Neither postprandial beta-EP nor ACTH increases were found at the 24th hour or on the fourth day of life. beta-EP physiology in newborn infants seems to be different from adults.     

Characterization of chloride transport pathways in cultured human keratinocytes.

In human keratinocytes, mediated transport of Cl- was found to occur mainly by two mechanisms: an anion exchange and an electrically conductive pathway. The contribution of the anion exchange, which accounted for about 50% of overall Cl- efflux, was assessed either by its sensitivity to inhibition by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), and by means of Cl- substitution experiments. The anion exchange exhibited a saturation behaviour over the range 10-135 mM Cl-; Cl- was more efficient than HCO3-, Br- and NO3- in increasing Cl- efflux rate, whereas SO4(2-) and I- inhibited Cl- efflux. The electrically conductive Cl- pathway, which accounted for about 40% of total Cl- efflux, was inhibited by the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and was at least partially sensitive to variation of the plasma membrane potential. The Cl- channel was insensitive to elevation in the intracellular concentration of either cyclic AMP and calcium ions. Indomethacin, an inhibitor of the cyclooxygenase, failed to reduce Cl- efflux, whereas nordihydroguaiaretic acid (NDGA), an inhibitor of the lipoxygenase, induced 50% inhibition of Cl- efflux. These results support the conclusion that endogenous production of lipoxygenase-derived arachidonic acid metabolite(s) might be responsible for high basal Cl- permeability in human keratinocytes.     

Chirality of reverse micelles

Four chiral analogues of the surfactant Aerosol-OT (AOT) have been synthesized and characterized. All of them form reverse micelles in apolar solvents in the w₀ range 0–30 (w₀ = [water]/[tenside]). Reverse micellar solutions have been investigated by UV absorption and circular dichroism spectroscopies with the aim of clarifying whether the formation of the macromolecular micellar structure induces the appearance of new chromophoric bands or perturbs the existing ones. Methanolic solutions of the surfactants, in which no micellar aggregates are formed, were taken as references. One of the products 1(S),1′(S)-dimethylbisheptylsulphosuccinate sodium salt (MH-AOT) was capable of forming reverse micelles of relatively high water content (w₀ up to 40) and this process was accompanied by a specific increase in the intensity of the circular dichroism band associated with the ester absorbance of the molecule. As no concomitant changes were seen in the UV absorbance spectrum, it was concluded that this observation reflected conformational events occurring within the surfactant rather than chromophoric perturbation. These results are qualitatively similar to those found recently for lecithin reverse micelles which, however, form gels at sufficiently high water contents. The chiroptical properties of these supramolecular aggregates are compared with those of covalent macromolecular systems such as polypeptides.     

Biochemical and morphological modifications in rabbit Achilles tendon during maturation and ageing.

1. The plasma clearance of intravenously injected 125I-labelled mitochondrial malate dehydrogenase (half-life 7 min) was not influenced by previous injection of suramin and/or leupeptin (inhibitors of intralysosomal proteolysis). 2. Pretreatment with both inhibitors considerably delayed degradation of endocytosed enzyme in liver, spleen, bone marrow and kidneys. 3. The tissue distribution of radioactivity was determined at 30 min after injection, when only 3% of the dose was left in plasma. All injected radioactivity was still present in the carcass. The major part of the injected dose was found in liver (49%), spleen (5%), kidneys (13%) and bone, including marrow (11%). 4. Liver cells were isolated 15 min after injection of labelled enzyme. We found that Kupffer cells and parenchymal cells had endocytosed the enzyme at rates corresponding to 9530 and 156 ml of plasma/day per g of cell protein respectively. Endothelial cells do not significantly contribute to uptake of the enzyme. 5. Uptake by Kupffer cells was saturable, whereas uptake by parenchymal cells was not. This suggests that these cell types endocytose the enzyme via different receptors. 6. Previous injection of carbon particles greatly decreased uptake of the enzyme by liver, spleen and bone marrow.     

Calcitroic acid: biological activity and tissue distribution studies

Calcitroic acid was recently identified as a major metabolite of 1,25-dihydroxyvitamin D₃ (Esvelt, Schnoes, and DeLuca, Biochemistry 18, 3977, 1979). The metabolite was found to have little, although significant, activity in healing rickets, and causing bone mineral mobilization but elicited no significant elevation in intestinal calcium transport. The compound showed little affinity for either the serum 25-hydroxyvitamin D binding protein or the intestinal cytosol receptor for 1,25-dihydroxyvitamin D₃. Various tissues of the rat were examined for the presence of calcitroic acid following a 120-ng dose of 1,25-dihydroxy-[3α-³H]vitamin D₃. The metabolite was detected in liver, intestinal mucosa, kidneys, and blood with livers and mucosa containing the highest concentrations. In each of these tissues the calcitroic acid content increased during the period between 4 and 12 h after the dose. The presence of calcitroic acid in femurs was indicated but could not be confirmed. Bile duct cannulation reduced but did not abolish the intestinal calcitroic acid content. In addition to calcitroic acid, other polar metabolites of 1,25-dihydroxyvitamin D₃ were detected in these experiments.     

Inhibition of the biosynthesis of thyroglobulin with propranolol in the rat

Thyroglobulin biosynthesis was studied in thyroid glands of rats treated during 30 days with a daily dose of propranolol, a non-selective beta-adrenergic blocking drug. Studies were carried out by extraction of soluble proteins from homogenates after incubation of the glands in presence of [3H]-4,5-L-leucine and [3H]-D-1-galactose. Thyroglobulin 19S, 12S and 4-8S soluble proteins were separated and identified by ultracentrifugation in a saccharose gradient. The glands of rats treated with propranolol showed a decreased amount of soluble proteins as well as a decreased incorporation of [3H] labeled markers. 19S thyroglobulin is poorly represented, but very large amounts of the 12S monomer are present; this suggests an impairment in the dimerization of the 12S subunit, absent in normal controls. This impairment could be due to a structure modification. Propranolol reduces the biosynthesis of thyroglobulin in thyroid gland as well as the formation of T3 from T4 in peripheral tissues; its therapeutical use against thyrotoxicosis is thus justified. The study of its action on the dimerisation of the 12S subunit could be of interest to clear the mechanism of thyroglobulin biosynthesis.