Protein brings cells into shape

Researchers demonstrate how the Spir protein works

Spir-Protein University of Würzburg
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A new basic cell biological mechanism has now been discovered by Würzburg cell researchers together with American colleagues. As the scientists report, the so-called Spir protein in the cell performs an important work: It mediates the formation of so-called actin filaments. In addition, the researchers suspect that it plays a role in breast cancer and the growth of nerve cells. The researchers report on their findings in the current issue of the science journal "Nature".

The spir protein discovered in the working group of Eugen Kerkhoff at the University of Würzburg by the PhD student Ines Otto five years ago initiates the polymerization of actin. This globular protein plays a crucial role in cell shape and cell movement. During polymerization, individual actin molecules are linked into long strands, which enable cells to change their structure, move or transport substances inside.

The polymerization does not proceed by itself. So far, science has known two mechanisms that initiate it, as Kerkhoff explains. But now a third way is on record, which runs on the spir protein. First, the protein binds four individual actin spheres. This creates a germ to which more balls can attach. This process of strand formation is described in detail by the Würzburg researchers with their colleagues from San Francisco and St. Louis in "Nature".

Spir is always in the cell near membrane bubbles, the so-called vesicles, which are used for material transport. "We suspect that the strand growing from the spir protein drives the bubbles, pushing them forward, so to speak, " says Kerkhoff.

Spir ensures polarity

On the other hand, researchers are certain that cells without the spir protein lose their polarity. Polarity means that cells are not all around the same, but that there are front and back, bottom and top. This is the case, for example, with the so-called epithelial cells: they cover surfaces, clothe the intestine or the blood vessels. If such cells lose their polarity, that is often the first step in the development of cancer, as the Würzburg researcher says. display

It is therefore conceivable that damage to the spir protein cancels the polarity of a cell and degenerates it into a cancerous cell. Interesting in this context: In 20 percent of all breast cancer patients antibodies are found in the blood, which are directed against one of the two known in humans Spir proteins. Kerkhoff is now exploring this connection between protein and breast cancer in cooperation with Ulf R. Rapp and Johannes Dietl from the Women's Hospital of the University of Würzburg. The Sander Foundation (Munich) supports the project.

In addition, the scientists at the Institute of Medical Radiation Science and Cell Research are also addressing another aspect: "We are also investigating the role of spir in the development of nerve cells and in the brain, " says Kerkhoff. For here, too, the protein seems to mix vigorously, and the polarity also plays a major role in nerve cells. Five years after the discovery of the protein, the researchers in Würzburg are still facing enough questions to await an answer.

(idw - University W rzburg, 31.01.2005 - DLO)