Blandine Mille-Baker

Mae mediates MAP kinase phosphorylation of Ets transcription factors in Drosophila.

The evolutionarily conserved Ras/mitogen-activated protein kinase (MAPK) cascade is an integral part of the processes of cell division, differentiation, movement and death. Signals received at the cell surface are relayed into the nucleus, where MAPK phosphorylates and thereby modulates the activities of a subset of transcription factors. Here we report the cloning and characterization of a new component of this signal transduction pathway called Mae (for modulator of the activity of Ets). Mae is a signalling intermediate that directly links the MAPK signalling pathway to its downstream transcription factor targets. Phosphorylation by MAPK of the critical serine residue (Ser 127) of the Drosophila transcription factor Yan depends on Mae, and is mediated by the binding of Yan to Mae through their Pointed domains. This phosphorylation is both necessary and sufficient to abrogate transcriptional repression by Yan. Mae also regulates the activity of the transcriptional activator Pointed-P2 by a similar mechanism. Mae is essential for the normal development and viability of Drosophila, and is required in vivo for normal signalling of the epidermal growth factor receptor. Our study indicates that MAPK signalling specificity may depend on proteins that couple specific substrates to the kinase.

Human Umbilical Vein Endothelial Cells Differ from Other Endothelial Cells in Failing to Express ABO Blood Group Antigens

Most in vitro investigations of endothelial cell function have been based on the behaviour of human umbilical vein endothelial cells (HUVEC) in primary tissue culture. However, it is becoming apparent that there is a marked degree of heterogeneity among endothelial cells derived from different vascular beds. We have studied primary HUVEC from 45 umbilical cords. Contrary to previously published reports, we were unable to detect ABO antigens on the surface of cultured HUVEC from group A or B cords. This was not due to an absence of precursor H substance which was uniformly expressed on HUVEC in primary tissue culture. Further investigation revealed an absence of A enzyme activity in A type HUVEC and a level of mRNA only just detectable by RT-PCR. The absence of functional A enzyme activity was confirmed by demonstrating the absence of A substance on von Willebrand factor secreted by A type cells. HUVEC appear to be the only vascular endothelial cells that do not express ABO blood group antigens. We speculate that this may help protect the cord from maternal antibodies during gestation. The lack of ABO blood group antigens on HUVEC may significantly affect their surface function, and therefore care should be taken when extrapolating conclusions from results obtained with these cells (the most widely used human endothelial cell model in vitro) to the properties of adult endothelial cells.

Awards of the ESM

This award entails a donation of 2,500 € to allow younger researchers in the area of microcirculatory and vascular biology research to visit research laboratories to learn new techniques. Personal applications as well as suggestions are invited. The candidate should provide a twopage curriculum vitae including a short section on scientific development and future perspectives. The top ranking applications will be rewarded by a free subscription of the Journal of Vascular Research for two years. Van Leeuwenhoek distinctive Travel Award 2000: Hans Vink (Amsterdam, The Netherlands) for his pioneering studies on the endothelial surface layer