Cell Talk
Research on the phenomenon of communication is often thought to be an exclusive domain of social scientists and psychologists. However, the mechanisms of information and signal exchange between the billions of cells composing the human body are also a central topic in the biological field. One such signalling system was unveiled by Dr. Friedhelm Bladt at the MAX-DELBRÜCK-CENTER FOR MOLECULAR MEDIClNE (MDC) BERLIN-BUCH, a national research laboratory in the Northeast of Berlin. These results have now been published in the British journal NATURE (Vol. 376, No. 6543, p. 768-772). The molecular biologist recently identified a signaling system which directs the migration of muscle cells during certain phases of embryogenesis. "As it appears this molecule also plays an important role in the development of cancer''', stresses Bladt.
In the News and Views column of the journal (p. 723), Richard Warn from the School of Biological Sciences, University of East Anglia, UK comments that this "new piece of scientific jigsaw fills a gap in the puzzle" of physiological and pathological processes. That "piece of jigsaw" is the c-met-receptor, a signal-transducing molecule of the cell membrane. Bladt and his colleagues were able to show that two prerequisites have to be fulfilled for successful limb muscle development: namely, the presence of an intact c-met-receptor and its corresponding partner molecule, a soluble protein produced by the cells of the adjacent tissue. This partner protein is known as "scatter" or "hepatocyte growth" factor (SF/HGF) .
Bladts experiments with mouse embryos showed that there would be no muscle-precursor cell migration into the limb buds if either of the two partners were missing or dysfunctional. All embryos producing defective c-met-receptor molecules due to c-met-gene manipulation die before being born. The whole signal-system consists of just these two molecules. Thus, the c-met-receptor/scatter factor duo constitutes a simple, though crucial regulation system.
Interestingly, the c-met-receptor molecule has been found to be involved in various other physiological processes, such as the regulation of liver regeneration. Yet, under certain circumstances, the receptor-molecule can develop destructive properties, which may contribute to the malignancy of tumors. Many carcinoma cells - they compose approximately 90 percent of all human tumors - carry abnormal c-met-receptor-molecules. Structural alterations of this molecule probably make cancer cells more invasive and more likely to cause metastases (tumor colonies in other organs). Massive overproduction of the molecule can be similarily dangerous.
Dr. Carmen Birchmeier-Kohler, in whose group Bladt works, describes a third mechanism, by which carcinoma cells may be initiated. She speculates that in many cases" a carcinoma cell conduct a dialogue with itself, instead of communicating with its neighbours. In other words, one cell produces both partners of the signalling duo, whereas in healthy tissue, one cell produces the scatter factor and another cell has the receptor to perceive it. This "autocrine loop" probably allows cancer cells to embark an unregulated and harmful vagabond journey through the body.
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