Research led by Francis Crick Institute scientists has revealed
insights into how a process called autophagy happens in cells, with
implications for increasing understanding of cancer and other human
diseases.
Dr Sharon Tooze of the Crick (currently based at Lincoln's
Inn Fields) said: "To remain healthy, cells must dispose of
their unwanted or damaged components. If these damaged components
accumulate, they can stop the cell performing its normal function,
resulting in diseases like Alzheimer's and Parkinson's disease, or
lead to DNA damage which can lead to cancer-causing mutations. One
of the main ways cells dispose of these potentially dangerous
materials is through a 'self-eating' process called autophagy.
"Autophagy can be thought of as a recycling system.
Unwanted cellular components are engulfed by unique membrane
compartments called autophagosomes. Autophagosomes act as
garbage trucks, carrying the unwanted material to the cell's
recycling plant, the lysosome. Here the autophagosome's
contents are broken down into their constituent parts which can be
re-used by the cell."
When a cell is stressed it can form dozens of autophagosomes in
just 15 minutes - this requires major reorganisation of the
membranes inside the cell. Dr Tooze's laboratory is working to
understand how autophagosomes form. One of the questions they are
addressing is how this reorganisation of membranes is controlled by
the cell.
In previous work the researchers discovered a protein called
TBC1D14 that helps to decode growth signals from the outside the
cell, and also controls the formation of autophagosomes. To
investigate how TBC1D14 works they used mass spectrometry, a
technique which allows them to identify unknown proteins which
associate with known proteins. This revealed that a multi-protein
assembly, known as the TRAPP complex, interacts with
TBC1D14.
The TRAPP complex acts in the cell to maintain essential
functions such as secretion, the process of releasing chemicals and
other molecules from a cell that is important for tissue and organ
function. Genetic mutations in the TRAPP complex cause a rare
disease that affects skeletal tissue.
Dr Tooze's team showed that TBC1D14 and the TRAPP complex act
together to control autophagy. This is important because it
provides a link between outside events, such as growth signals
(through TBC1D14), and those required to maintain the cell's
environment (via the TRAPP complex) with the autophagy response to
stress. The scientists suggest that these links allow the cell to
respond to variations in its normal function by activating a
survival pathway.
Dr Tooze said: "Autophagy increases when cells are stressed,
such as in starvation conditions. This is what happens in many
tumours and it is thought that cancer cells exploit autophagy to
survive this starvation. Understanding how autophagy is controlled
is important, as the process can either protect against or support
disease progression in different contexts."
"Our work into the fundamental process of how proteins interact
may also help in understanding other human diseases, such as rare
diseases that arise by unexpected changes in a cell's
proteins."
The paper, TBC1D14 regulates autophagy via the TRAPP complex and ATG9
traffic, is published in the EMBO Journal.