Fusion confusion: new paper on FGFR3-TACC3 fusions in cancer

We have a new paper out! This post is to explain what it’s about.

Cancer cells often have gene fusions. This happens because the DNA in cancer cells is really messed up. Sometimes, chromosomes can break and get reattached to a different one in a strange way. This means you get a fusion between one gene and another which makes a new gene, called a gene fusion. There are famous fusions that are known to cause cancer, such as the Philadelphia chromosome in chronic myelogenous leukaemia. This rearrangement of chromosomes 9 and 22 result in a fusion called BCR-ABL. There are lots of different gene fusions and a few years ago, a new fusion was discovered in bladder and brain cancers, called FGFR3-TACC3.

Genes encode proteins and proteins do jobs in cells. So the question is: how are the proteins from gene fusions different to their normal versions, and how do they cause cancer? Many of the gene fusions that scientists have found result in a protein that continues to send a signal to the cell when it shouldn’t. It’s thought that this transforms the cell to divide uncontrollably. FGFR3-TACC3 is no different. FGFR3 can send signals and the TACC3 part probably makes it do this uncontrollably. But, what about the TACC3 part? Does that do anything, or is this all about FGFR3 going wrong?

What is TACC3?

Chromosomes getting shared to the two daughter cells

TACC3, or transforming acidic coiled-coil protein 3 to give it its full name, is a protein important for cell division. It helps to share the chromosomes to the two daughter cells when a cell divides. Chromosomes are shared out by a machine built inside the cell called the mitotic spindle. This is made up of tiny threads called microtubules. TACC3 stabilises these microtubules and adds strength to this machine.

We wondered if cancer cells with FGFR3-TACC3 had problems in cell division. If they did, this might be because the TACC3 part of FGFR3-TACC3 is changed.

We weren’t the first people to have this idea. The scientists that found the gene fusion suggested that FGFR3-TACC3 might bind to the mitotic spindle but not be able to work properly. We decided to take a closer look…

What did you find?

First of all FGFR3-TACC3 is not actually bound to the mitotic spindle. It is at the cells membrane and in small vesicles in the cell. So if it is not part of the mitotic spindle, how can it affect cell division? One unusual thing about TACC3 is that it is a dimer, meaning two TACC3s are stuck together. Stranger than that, these dimers can stick to more dimers and multimerise into a much bigger protein. When we looked at the normal TACC3 in the cell we noticed that the amount bound to the spindle had decreased. We wondered whether the FGFR3-TACC3 was hoovering the normal TACC3 off the spindle, preventing normal cell division.

We made the cancer cells express a bit more normal TACC3 and this rescued the faulty division. We also got rid of the FGFR3-TACC3 fusion, and that also put things back to normal. Finally, we made a fake FGFR3-TACC3 which had a dummy part in place of FGFR3 and this was just as good at hoovering up normal TACC3 and causing cell division problems. So our idea seemed to be right!

What does this mean for cancer?

This project was to look at what is going on inside cancer cells and it is a long way from any cancer treatments. Drug companies can develop chemicals which stop cell signalling from fusions, these could work as anti-cancer agents. In the case of FGFR3-TACC3, what we are saying is: even if you stop the signalling there will still be cell division problems in the cancer cells. So an ideal treatment might be to block TACC3 interactions as well as stopping signalling. This is very difficult to do and is far in the future. Doing work like this is important to understand all the possible ways to tackle a specific cancer and to find any problems with potential treatments.

The people

Sourav Sarkar did virtually all the work for this paper and he is first author. Sourav left the lab before we managed to submit this paper and so the revision experiments requested by the peer reviewers were done by Ellis Ryan.

Why didn’t we post this paper as a preprint?

My group have generally been posting our new manuscripts as preprints while they undergo peer review, but we didn’t post this one. I was reluctant because many cancer journals at the time of submission did not allow preprints. This has changed a bit in the last few months, but back in February several key cancer journals did not accept papers that had appeared first as preprints.

The title of the post comes from “Fusion Confusion” 4th track on the Hazy EP by Dr Phibes & The House of Wax Equations.


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