Researchers from North Carolina State University have developed a new
technique to identify the proteins secreted by a cell. The new approach should help
researchers collect precise data on cell biology, which is critical in fields
ranging from zoology to cancer research.
The work is important because cells communicate by secreting proteins. Some of
the proteins act on the cell itself, telling it to grow or multiply, for
example. But the proteins can also interact with other cells, influencing them
to perform any biological function.
Traditionally, scientists who wanted to identify these proteins cultured
cells and then used mass spectrometry to determine which proteins appeared in
the medium the cell was grown on. This has drawbacks, because the proteins of
interest are fairly rare compared to the proteins that are already in the medium—which
are used to grow and support the cells in the first place. Further, any
attempts to culture the cells without these background, supporting proteins
affects cell behavior—skewing the sample.
The new approach takes advantage of the fact that each cell “packages” its
proteins in its “secretory pathway.” Each cell synthesizes the protein and
passes it through this pathway, essentially placing it in a bag-like membrane
before it is passed out of the cell.
In their new technique, researchers take a sample of cells and isolate the
secretory pathway organelles, which contain the proteins. The researchers then
use mass spectrometry to analyze the contents of the organelles, in order to
see which proteins were being secreted by the cell. Using this approach, the
researchers were able to identify proteins that are secreted by human embryonic
stem cells.
“This gives us a snapshot of exactly what a cell was secreting at that point
in time,” says Balaji Rao, an assistant professor of chemical and biomolecular
engineering at NC State and co-author of a paper describing the work.
This new method eliminates the problems related to the proteins found in
cell culture media. But it also allows researchers to track changes in the
proteins released by a cell in response to a stimulus, such as exposure to a
chemical. This can be done by taking samples at various points in time after
cells have been exposed to the stimulus.
And, in principle, this technique would also allow researchers to identify
which proteins any specific type of cell is secreting when in a mixed
population of cells.
“As long as you can separate the cells you are interested in, this should be
possible,” says Rao. “And that is important, because most tissues are made up
of heterogeneous populations of cells—and communication between those cells is
biologically significant.”
The paper, “Targeted proteomics of the secretory pathway reveals the
secretome of mouse embryonic fibroblasts and human embryonic stem cells,” was
published online by Molecular & Cellular Proteomics.
Source: North Carolina State University
