|Summary of Croix et al|
New solutions to an old question
Tumor angiogenesis is a process of clinical relevance, thus the molecular steps involved are of particular interest. Traditional approaches to link altered gene expression to the clinical phenotype were mostly focused on the analysis of single gene effects. Recently developed high true put approaches have provided a way to study functional relationships on a multifactorial bases, allowing the characterization of a process, a network rather than a gene, a nodal point of a network. Such techniques have increasingly been used in the description of angiogenesis, mostly relying on in vitro endothelial systems that allow a controlled switch between different phenotypical steps.
The publication that initiated this protein study
A SAGE-analysis performed by Croix et al, aimed at uncovering genes expressed differentially in tumor-associated versus normal endothelium. Such genes supply a molecular basis for understanding the process of angiogenesis and are of potential interest for the development of anti-angiogenic cancer therapies. The approach taken by the researchers in their study is outlined in the following:
Isolation of endothelial cells from tissue specimens is a difficult task as the cells of interest constitute only a small fraction of the cells in a particular tissue.Human colon cancer was chosen for the study for its high incidence, and angiogenesis dependent growth. Negative selection of non-endothelial cells was achieved in multiple steps applying mechanical and immunological techniques. Positive selection of endothelial cells was based on immunological methods.
SAGE analysis of the obtained material results in the generation of SAGE-libraries for non-endothelial and endothelial cells containing around 96 000 tags each (corresponded to over 16 000 transcripts each). Differentially expressed tags were classified as follows:
PEMs, pan endothelial markers. They are expressed preferentially in tumor-associated and normal endothelium compared to other cell-types. A total of 93 tags matching this category have been published.
TEMs, tumor endothelial markers. They are expressed preferentially in tumor-associated compared to normal endothelium. A total of 46 tags matching this category have been published.
NEMs, normal endothelial markers. They are expressed preferentially in normal compared to tumor-associated endothelium. A total of 33 tags matching this category have been published.
Besides the advantages that are common to the SAGE analysis, the use of in vivo material isolate from normal and tumor tissue allows an unbiased characterization of an angiogenic endothelium transcription profile.