title: H-Ras increases release of sphingosine resulting in down-regulation of TSP-1 in non-transformed cells.
abstract: Tumour progression is continuously driven by a sequence of genetic events. The presence of mutant or activated Ras proteins represents an interesting paradigm for the investigation of oncogene-dependent induction of tumour angiogenesis. These genes are widely distributed in human cancers. Previously we have shown that cells harbouring mutant H-Ras release soluble unidentified factor(s) associated with lowered expression of an angiogenesis inhibitor - Thrombospondin-1 - (TSP-1) in adjacent normal tissue. In this study, we have addressed the question as to whether or not introduction of the H-ras oncogene leads to increased production of sphingosine. To assess the amount of sphingosine in conditioned media, we developed a technique based on sphingolipid isolation and GC-MSMS detection of specific silylated sphingosine derivatives. Cells harbouring mutant H-Ras, release significant amounts of sphingosine in contrast to normal isogenic cells or premalignant cells. Increased concentration of sphingosine in conditioned media was correlated with their ability to down-regulate the expression of TSP-1. Moreover, medium collected in the presence of U0126, an inhibitor of MAPK kinase (MEK), contained undetectable amounts of sphingosine and had no ability to down-regulate TSP-1 expression. Overall, our studies suggest a H-Ras-dependent mechanism of changing the equilibrium of angiogenic factors in favour of induction of angiogenesis, where a central role is played by sphingosine, a low molecular entity. This represents an example of how a mechanism of translating genetic changes within transformed cells could be amplified into a much larger effect involving the tumour parenchyma and stroma, and this could greatly in turn accelerate local tumour growth and metastasis.
authors.affiliation: Department of Experimental Oncology, Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Wroclaw, Poland. kalas@iitd.pan.wroc.pl
authors.forename: Wojciech
authors.initials: W
authors.lastname: Kalas
authors.forename: Jacek
authors.initials: J
authors.lastname: Rybka
authors.forename: Ewelina
authors.initials: E
authors.lastname: Swiderek
authors.forename: Ewa
authors.initials: E
authors.lastname: Ziolo
authors.forename: Wojciech
authors.initials: W
authors.lastname: Rybka
authors.forename: Andrzej
authors.initials: A
authors.lastname: Gamian
authors.forename: Janusz
authors.initials: J
authors.lastname: Rak
authors.forename: Leon
authors.initials: L
authors.lastname: Strzadala
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D015536:Down-Regulation / Q000502:physiology*; D011905:Genes, ras / Q000235:genetics*; D051379:Mice; D011401:Promoter Regions, Genetic; D013110:Sphingosine / Q000235:genetics / Q000378:metabolism*; D019700:Thrombospondin 1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D019700:Thrombospondin 1; D013110:Sphingosine