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Until recently, the only accepted mechanism of tumour vascularization was the sprouting of endothelial cells (EC) from pre-existing vessels, while recent studies suggest the contribution of stem cell-derived endothelial progenitors as well as cells from the myeloid lineage. Here, we show a new way of endothelial differentiation that involves the specific modulation of monocytes by the tumour environment. The tumour milieu is characterized by the presence of cytokines and lactate which induce the differentiation of tumour-invading monocytes into tumour-associated dendritic cells (DC). Additional incubation of tumour-associated DC with pro-angiogenic factors, such as vascular endothelial growth factor and oncostatin M, led to transdifferentiation into endothelial-like cells. The cells showed strong expression of von Willebrand factor and VE-Cadherin, both classical EC markers, while leukocytic markers were reduced. In addition, they were able to form network-like structures on matrigel, which could be blocked by the DNA-based drug Defibrotide. This finding may be of great therapeutic relevance for tumour therapy.

Traditionally, heat shock proteins (HSPs) are believed to be located intracellularly, where they perform a variety of chaperoning functions. Recently, evidence has accumulated that some tumor cells express HSPs on the cell surface. The present study confirms this finding and correlates HSP72 cell surface expression, induced by nonlethal heat shock, with an increased sensitivity to interleukin-2-stimulated CD3- natural killer (NK) cells. After nonlethal heat shock, a monoclonal antibody directed against the major heat-inducible 72-kD HSP (HSP72) stains the cell surface of sarcoma cells (ie, Ewing's sarcoma cells or osteosarcoma cells) but not that of normal cells (ie, peripheral blood lymphocytes, fibroblasts, phytohemagglutin-stimulated blasts, B- lymphoblastoid cell lines) or of mammary carcinoma cell line MX-1 carcinoma cells. In this study, we show for the first time a correlation of HSP72 cell surface expression with an increased susceptibility to lysis by NK effector cells. This finding is supported by the following points: (1) HLA-disparate effector cells show similar, elevated lysis of HSP72+ heat-treated sarcoma cells; (2) CD(3-) NK cells, but not CD3+ cytotoxic T lymphocytes, are responsible for the recognition of heat-shocked sarcoma cells; (3) by antibody-blocking studies, an immunogenic HSP72 determinant, which is expressed selectively on the cell surface of heat-treated sarcoma cells could be correlated with NK recognition; (4) the reported phenomenon is independent of a heat-induced, transient downregulation of major histocompatibility complex (MHC) class-I expression; and (5) blocking of MHC class-I-restricted recognition, using either MHC class-I- specific monoclonal antibody W6/32 on the target cells or alpha/beta T- cell receptor monoclonal antibody WT31 on effector cells, also has no inhibitory effect on the lysis of HSP72+ tumor cells. Finally, our in vitro data might have further clinical implications with respect to HSP72 as a stress-inducible, sarcoma-specific NK recognition structure.

Human Hep27 was originally isolated from growth-arrested HepG2 cells and identified as a member of the superfamily of short-chain dehydrogenases/reductases (SDR). Its substrate specificity has not been determined, but a cross-species comparison suggests that it occurs in widely divergent species, such as human, Cenorhabditis elegans, Drosophila and Arabidopsis thaliana. In this study, Hep27 was expressed as a His(6) fusion protein, and subjected to a substrate screen, using a compound library of SDR substrates, comprising steroids, retinoids, sugars and carbonyl compounds. Whereas no steroid dehydrogenase or retinoid activity was detected, it was found that Hep27 catalyzed the NADPH-dependent reduction of dicarbonyl compounds, like 3,4-hexanedione and 1-phenyl-1,2-propanedione with similar turnover numbers as DCXR (a mitochondrial dicarbonyl reductase/xylulose reductase). In contrast, Hep27 does not convert sugar substrates like xylulose or threose. Based on its substrate specificity and expression in endothelial tissues, it is suggested that Hep27 functions as a dicarbonyl reductase in enzymatic inactivation of reactive carbonyls, involved in covalent modification of cellular components.