Molecular Mechanisms

MOLECULAR MECHANISMS HOMEOBOX GENES: THEIR POTENTIAL ROLE IN CONTROLLING THE ANGIOGENIC PHENOTYPE OF ENDOTHELIAL CELLS BELOTTI DORINA, CLAUSSE NATHALIE , PAGANONI PAOLA, DEROANNE CHRISTOPHE , NUSGENS BETTY. V. , GIAVAZZI RAFFAELLA, TARABOLETTI GIULIA, CASTRONOVO VINCENT 2 1 Laboratory of Biology and Treatment of Metastasis, M. Negri Institute for Pharmacological Research, Bergamo, Italy 2 Metastasis Research Laboratory, University of Liege, Liege, Belgium 3 Connective Tissues Biology Laboratory, University of Liege, Liege, Belgium Homeobox genes are a family of transcription factors controlling cell proliferation and differentiation in embryogenesis, neoplasia and hematopoiesis. We are testing the hypothesis whether some members of HOX genes are involved in the control of the differentiation-like process of endothelial cells occurring during angiogenesis. We have previously shown that the expression of HOX genes from cluster B in human umbilical vein endothelial cells (HUVEC) is modulated in a time-dependent manner by vascular endothelial growth factor (VEGF) and by the phorbol esther TPA, an agent known to induce differentiation of endothelial cells. The aim of this study was to compare the expression of HOX genes from cluster A, B, C and D in HUVEC in resting conditions and in angiogenic conditions. For this purpose HUVEC were grown in a two dimension culture of collagen type I gel (resting endothelium) or plated in a sandwich between two layers of collagen type I gel where they were stimulated to form capillary-like structures (angiogenic endothelium). RT-PCR experiments using specific primers for each human HOX gene of class I were performed and a different combination of HOX genes expression was found in resting and angiogenic endothelium. In particular this screening led to the identification of a class I HOX gene which could potentially participate in the tubulogenesis process and therefore in the control of new blood vessel formation. At this step of the study some HOX genes seem to be implicated in the regulation of the angiogenic phenotype of endothelial cells. PICOLINIC ACID AND HYPOXIA DIFFERENTIALLY REGULATE CHEMOKINE EXPRESSION IN MACROPHAGES BOSCO MARIA CARLA, RAPISARDA ANNAMARIA, MASSAZZA STEFANO, PASTORINO SANDRA, DAZZI CECILIA, MELILLO GIOVANNI, VARESIO LUIGI Laboratory of Molecular Biology, G. Gaslini Institute, Genova, Italy Angiogenesis is an essential process for tumor growth and metastasis, regulated by the local balance between stimulatory and inhibitory signals. A potent inducer of angiogenesis is hypoxia, a common feature of solid tumors that strongly correlates with tumor progression, resistance to chemoand radiotherapy, and poor prognosis. Hypoxiaregulated genes encoding for angiogenic factors have been described in mononuclear phagocytes. We have reported that hypoxia stimulates human monocytes to produce the vascular endothelial growth factor, VEGF, and that murine macrophages respond to hypoxia with the transcriptional activation of the inducible nitric oxide synthase (iNOS) and the consequent production of nitric oxide (NO), a pleiotropic molecule implicated in angiogenesis. Moreover, we have recently demonstrated that the macrophage activator picolinic acid (PA), an end-product of L-tryptophan catabolism detected in human milk and in the serum of patients with chronic liver conditions, shares with hypoxia the ability of inducing NO production, thus suggesting a potential involvement of this metabolite in the angiogenic process. Recently, an important pathophysiological role for chemokines in the regulation of tumor angiogenesis has been proposed. Chemokines with angiogenic properties have been identified, and a vast literature associates their presence with cancer. Yet, the nature of the signals that elicit chemokine production in the tissue microenvironment has not been fully elucidated. In this study, we have investigated the ability of PA and hypoxia to modulate the expression pattern of several α and β chemokines in macrophages, and we have analyzed the molecular mechanisms involved. Our findings demonstrate a differential regulation of chemokine expression by the two stimuli in macrophages. We show that PA is a potent and selective inducer of MIP-1α/MIP-1β chemokine expression and that hypoxia can exhert a profound inhibitory effect on the constitutive and IFNγor LPS-induced MCP-1 production. ABSTRACTS bio 4 17-12-1999 16:13 Pagina 278