It will be interesting to see how secretion changes when you treat a cell with a particular drug. This can be an indicator of a change in cellular properties as a response to that drug.
Dr Jeroen Krijgsveld
Scientists at the European Molecular Biology Laboratory
(EMBL) along with colleagues from the German Cancer Research Center
(DKFZ) have designed an approach to cell culturing which allows them to monitor the proteins cells release to communicate with each other. The research appeared this week in the journal Nature Biotechnology
Although it is routine procedure to grow and sustain cells in the laboratory in a ten per cent serum, this serum contains proteins which inevitably complicate efforts to observe the secretory products of the cells and distinguish these from proteins already present in the foodstuff.
Researchers in Heidelberg have devised a new method which works by inducing the cells to use an artificial amino acid rather than methionine when they build proteins, allowing them to distinguish between proteins present in the serum and those made by the cells under investigation. The technique also enables the scientists to monitor how secretion changes over time, at two-hour intervals.
Cells secrete proteins for a reason – to communicate a signal to other cells or tissues which create a response in turn. Understanding and effectively listening in to these cellular ‘conversations’ was a strong motivation in initiating the study, as Dr Jeroen Krijgsveld, head of the Proteomic Core Facility at EMBL, explained.
What challenges are presented by culturing cells in protein-containing serums?
The problem lies in identifying the molecules that are secreted by the cell among all those serum proteins. What people have done to circumvent this is to grow cells without the serum, but this is quite an artificial system and sometimes damaging to the cells. Creating these stressful conditions may not be desirable because it is effectively starving the cells. Some die; they just don’t like it.
What is innovative about the technique that you have developed? What method does it use to solve the problem?
The trick we applied is to introduce a chemical tool to isolate the cell-secreted proteins from the cell supernatants, with or without serum. In a way this means it is irrespective of culture conditions. It allows a much broader range of applications and allows cells to be studied in their favoured conditions, including in serum.
We also applied a quantitative component, making it possible to identify not only what is there but also to quantify it between conditions, for example. We can now quantitatively compare cells treated in one way to untreated cells and observe what is secreted specifically upon cellular stimulation.
How important is the ability to measure changes in secretion over time?
It is important for studying the responsiveness of cells. One of the examples we used in the paper is the stimulation of macrophages. When you treat these cells, a different set of proteins is secreted early compared to later; their secretory profile changed over time. If you want to understand the mechanism of this process you need to do it in a time series, and we now have the ability to do this.
How do you plan to put the technique into use for the study of cancer drugs?
We have no specific data as yet, but this is an idea that we want to pursue. It will be interesting to see how secretion changes when you treat a cell with a particular drug. This can be an indicator of a change in cellular properties as a response to that drug. It may tell you something about the mechanism by which the drug works; if you know the pathway via which a particular protein is secreted it might give you a link to a drug.
At the same time we are also planning to compare cells which may or may not be sensitive to a certain drug and observe how their secretion differs, which could give an indication of particular properties of a cell which make them sensitive or resistant. This can have predictive value with regard to cell properties, and help to decide whether a treatment makes sense or not. Although this is looking into the future and may be wishful thinking, there is hopefully great potential here.
Do you envisage further refinements and wider possibilities for this new approach?
We are still looking into the chemistry that is being used. We are trying to get rid of interference from some background proteins by adjusting the chemistry. That is the most important thing right now. We have tried some alternative cell types, but I think this can be investigated in greater detail and in a wider range of cells.