Proteome analysis of migrating versus nonmigrating rat heart endothelial cells reveals distinct expression patterns.

Migration of endothelial cells plays an important role during angiogenesis and the late remodeling phase of arteriogenesis. To investigate mechanisms responsible for cell migration, the authors subcloned a rat heart endothelial cell line (RHE) into a migrating and a nonmigrating cell line (RHE-A and RHE-neg, respectively). Both cell lines form cobblestone patterns in confluent cultures similar to the originating cell line, but RHE-neg cells grow in dense cell islets of several layers whereas RHE-A cells grow in a less dense monolayer. Both cell lines show the same expression pattern of known endothelial cell surface antigens (e.g., FIK-1). The authors used two-dimensional gel electrophoresis technique to look for differentially regulated proteins with possible functional importance for cell migration. The analysis of the cytosolic fraction as well as the membrane fraction revealed differences in the protein expression patterns of RHE-neg and RHE-A cells. Regulated spots were isolated and analyzed by mass spectrometry (MS/MS technique), leading to the identification of proteins potentially responsible for endothelial cell migration, e.g., the intermediate filament vimentin that was exclusively expressed in RHE-A cells. The authors thus have generated a reproducible model that allows the analysis of the proteome responsible for endothelial cell migration.

Apoptotic DNA fragmentation is not related to the phosphorylation state of histone H1.

Changes in chromatin structure, histone phosphorylation and cleavage of DNA into nucleosome-size fragments are characteristic features of apoptosis. Since H1 histones bind to the site of DNA cleavage between nucleosomal cores, the question arises as to whether the state of H1 phosphorylation influences the rate of internucleosomal cleavage. Here, we tested the relation between DNA fragmentation and H1 phosphorylation both in cultured cells and in vitro. In Jurkat cells, hyperosmotic mannitol concentration resulted in apoptosis, including nucleosomal fragmentation, whereas apoptosis induction by increased NaCl concentration was not accompanied by DNA fragmentation. However, both treatments induced dephosphorylation of H1 histones. In contrast, treatment of Raji cells with alkylphosphocholine led to induction of apoptosis with internucleosomal fragmentation, albeit without notable histone H1 dephosphorylation. These results demonstrate that dephosphorylation of H1 histones is neither a prerequisite for nor a consequence of internucleosomal cleavage. Moreover, we observed with an in vitro assay that the known enhancing effect of H1 histones on the activity of the apoptosis-induced endonuclease DFF40 is independent of the subtype or the phosphorylation state of the linker histone.