Could help develop treatments to prevent metastasis (awesome animated video)
Metastasis (spread of cancer) is one of the biggest challenges in cancer treatment. It is often not the original tumor that kills, but secondary growths. But a key question in cancer research has been how vulnerable cancer cells are able to survive once they break away from a tumor to spread around the body.
“Metastasis is currently incurable and remains one of the key targets of cancer research,” said lead researcher Stéphanie Kermorgant, PhD, from Barts Cancer Institut at Queen Mary University of London (QMUL). “Our research advances the knowledge of how two key molecules communicate and work together to help cancer cells survive during metastasis. We’re hoping that this might lead to the discovery of new drugs to block the spread of cancer within the body.”
The study, published in an open-access paper in Nature Communications, examined the changes that occur in cancer cells as they break away from tumors in cell cultures in mice and zebrafish*. The research revealed a previously unknown survival mechanism in cancer cells and found that molecules known as “integrins” could be key.
Integrins are proteins on the cell surface that attach to and interact with the cell’s surroundings. “Outside-in” and “inside-out” signaling by integrins is known to help the cancer cells attach themselves to their surroundings.
Key discovery: “inside-in” signaling
But the study suggests that when the cancer cells are floating, as they do during metastasis, the integrins switch from their adhesion role to take on an entirely new form of communication that has never been seen before: “Inside-in” signaling, in which integrins signal within the cell.
The researchers discovered that an integrin called beta-1 (β1) pairs up with another protein called c-Met and they move inside the cell together. The two proteins then travel to an unexpected location within the cell that is normally used to degrade and recycle cell material. Instead, the location is used for a new role of cell communication and the two proteins send a message to the rest of the cell to resist against death while floating during metastasis.
Using both breast and lung cells, the team found that metastases were less likely to form when β1 and c-Met were blocked from entering the cell together or were prevented from moving to the special location within the cell.
Integrins are already major targets for cancer treatment with drugs either being tested or in use in the clinic. Most integrin inhibitor drugs target their adhesive function and block them on the surface of the cancer cell. The researchers say that the limited success of these drugs could be partly explained by this newly discovered role of integrins within the cancer cell.
Keeping the integrins out of the cancer cell
But a new strategy could be to prevent the integrin from going inside the cell in the first place. The researchers hope that these insights could lead to the design of better therapies against metastasis and more effective treatment combinations that could prevent and slow both tumor growth and spread.
The research was funded by the UK Medical Research Council, Breast Cancer Now, Rosetrees Trust, British Lung Foundation, Cancer Research UK and Barts Charity.
* The team carried out part of their animal research work on zebrafish embryos to implement the principle of 3Rs (refine, reduce, replace) on their research on mice. Zebrafish provide a similar tumor microenvironment to humans, meaning fewer tests need to be carried out in mice and any future experiments in mice will have been optimized to have minimal toxicity. They are aiming to reduce the number of mice used by at least 90 per cent and ultimately use zebrafish to completely replace the use of mice.
BCIQMUL | BCI Tumor Biology: integrins and metastasis
Abstract of Beta 1-integrin–c-Met cooperation reveals an inside-in survival signalling on autophagy-related endomembranes
Receptor tyrosine kinases (RTKs) and integrins cooperate to stimulate cell migration and tumour metastasis. Here we report that an integrin influences signalling of an RTK, c-Met, from inside the cell, to promote anchorage-independent cell survival. Thus, c-Met and β1-integrin co-internalize and become progressively recruited on LC3B-positive ‘autophagy-related endomembranes’ (ARE). In cells growing in suspension, β1-integrin promotes sustained c-Met-dependent ERK1/2 phosphorylation on ARE. This signalling is dependent on ATG5 and Beclin1 but not on ATG13, suggesting ARE belong to a non-canonical autophagy pathway. This β1-integrin-dependent c-Met-sustained signalling on ARE supports anchorage-independent cell survival and growth, tumorigenesis, invasion and lung colonization in vivo. RTK–integrin cooperation has been assumed to occur at the plasma membrane requiring integrin ‘inside-out’ or ‘outside-in’ signalling. Our results report a novel mode of integrin–RTK cooperation, which we term ‘inside-in signalling’. Targeting integrin signalling in addition to adhesion may have relevance for cancer therapy.