ADAM17/EGFR axis promotes transglutaminase-dependent skin barrier formation through phosholipase C gamma 1 and protein kinase C pathways

This work was supported by the German Research Foundation DFG (SFB 850/B6) and by the Fritz-Thyssen foundation (Az.10.14.2.150) to C.-W.F and the Medical Research Council (MR/L010402/1) to D.P.K

HOX-mediated LMO2 expression in embryonic mesoderm is recapitulated in acute leukaemias

The Lim Domain Only 2 (LMO2) leukaemia oncogene encodes an LIM domain transcriptional cofactor required for early haematopoiesis. During embryogenesis, LMO2 is also expressed in developing tail and limb buds, an expression pattern we now show to be recapitulated in transgenic mice by an enhancer in LMO2 intron 4. Limb bud expression depended on a cluster of HOX binding sites, while posterior tail expression required the HOX sites and two E-boxes. Given the importance of both LMO2 and HOX genes in acute leukaemias, we further demonstrated that the regulatory hierarchy of HOX control of LMO2 is activated in leukaemia mouse models as well as in patient samples. Moreover, Lmo2 knock-down impaired the growth of leukaemic cells, and high LMO2 expression at diagnosis correlated with poor survival in cytogenetically normal AML patients. Taken together, these results establish a regulatory hierarchy of HOX control of LMO2 in normal development, which can be resurrected during leukaemia development. Redeployment of embryonic regulatory hierarchies in an aberrant context is likely to be relevant in human pathologies beyond the specific example of ectopic activation of LMO2

Effects of Calcium on Structure and Function of the Human Red Blood Cell Membrane

The intracellular activity of ionized Ca++ in the red cell is below 0.4 nmoles/1 (Schatzmann, 1973; Simons, 1982; Lew et al., 1982b) and hence much lower than calculated from intracellular Ca++ content divided by red cell volume (Lichtman and Weed, 1973). This indicates that much of the Ca++ is bound to the cell membrane (Lichtman and Weed, 1973; La Celle et al., 1973; Porzig and Stoffel, 1978) and intracellular constituents. The latter include the phosphoric acid esters and hemoglobin (Ferreira and Lew, 1977), all of which act as Ca++ buffers. The low intracellular Ca++ activity is maintained although the membrane is leaky for Ca++ (Ferreira and Lew, 1977) and the concentration of free Ca++ in blood plasma (about 1200 nmoles/1) exceeds that in cytosol by about four orders of magnitude. The enormous gradient is balanced by a powerful Ca++ pump (for review see Schatzmann, 1983). At 37°C, the maximal rate of pumping is about 10 mmoles/1 cells/h. The half saturation concentration (K1/2) of the pump, and hence one of the essential factors that determines tne steady state Ca++ concentration, depends on the conditions inside the cell: the concentration of the energy supplying substrate ATP, the concentration of the activating calmodulin, and the concentration of Mg++ (calmodulin activates maximally when 1 Mg++ and 3 Ca++ ions are complexed). Under physiological conditions, K1/2 seems to be about 0.3 µmole/1 (Downes and Michel1, 1981)

Effects of intracellular Ca²⁺ and proteolytic digestion of the membrane skeleton on the mechanical properties of the red blood cell membrane

Intracellular Ca2+ at concentrations ranging from 0 to 10 mumol/l increases the shear modulus of surface elasticity (mu) and the surface viscosity (eta) of human red blood cells by 20% and 70%, respectively. K+ selective channels in the red cell membrane become activated by Ca2+. The activation still occurs to the same extent when the membrane skeleton is degraded by incorporation of trypsin into resealed red cell ghosts, suggesting that the channel activation is not controlled by the proteins of the membrane skeleton and is independent of mu and eta. Incorporation of trypsin at concentrations ranging from 0 to 100 ng/ml into red cell ghosts leads to a graded digestion of spectrin, a cleavage of the band 3 protein and a release of the binding proteins ankyrin and band 4.1. These alterations are accompanied by an increase of the lateral mobility of the band 3 protein which, at 40 ng/ml trypsin, reaches a plateau value where the rate of lateral diffusion is enhanced by about two orders of magnitude above the rate measured in controls without trypsin. Proteolytic digestion by 10-20 ng/ml trypsin leads to a degradation of more than 40% of the spectrin and increases the rate of lateral diffusion to about 20-70% of the value observed at the plateau. Nevertheless, mu and eta remain virtually unaltered. However, the stability of the membrane is decreased to the point where a slight mechanical extension, or the shear produced by centrifugation results in disintegration and vesiculation, precluding measurements of eta and mu in ghosts treated with higher concentrations of trypsin. These findings indicate that alterations of the structural integrity of the membrane skeleton exert drastically different effects on mu and eta on the one hand and on the stability of the membrane on the other