We are trying to find new genes which are upregulated, mutated or whatever in breast cancer that will give us leads to new pathways, oncogenic pathways, involved in cancer. Lately I became particularly interested in a group of genes called R-spondins which are actually secreted factors which may help to maintain stem cell activity. These genes also cause the stem cells to become eventually tumorigenic if these R-spondins are highly over-expressed. We found these genes by a method called insertion mutagenesis. These days people look for new genes using whole genome sequencing in tumours, another method is insertion mutagenesis and both pros and cons for the insertion mutagenesis or the whole genome sequencing but we happen to do the insertion mutagenesis. That brought us about thirty new genes, most of them have not been recognised as oncogenes before. So that’s just a summary of what I am doing.
Could this stem cell behaviour be blocked or reversed?
That’s quite interesting because in colon cancer there are R-spondins which are over-expressed. In about 10% of the colon cancers the R-spondins are stimulating the Wnt pathway, the Wnt pathway is very essential in colon cancer, and usually that is done by APC mutations. But in about 10% there are also R-spondins and they are mutually exclusive with the APC mutations indicating that they are active in the same pathway.
Not so long ago a paper appeared where they used antibodies against R-spondins in a xenograft model in mice. This was a model where the R-spondins were over-expressed instead of APC and when they gave these mice antibodies against R-spondins the tumours shrank, they even disappeared. So that would be a potential way also in other cancers where R-spondins are essential for the growth as a form of therapy; it could be used maybe in the future.
Are all the 30 genes spondin associated?
No, no, there are a whole scale of genes. Recently published another gene which is IRS4, insulin receptor substrate, that for instance becomes upregulated, at least in our model systems, when HER2 breast cancers are treated with lapatinib or trastuzumab or any of these new medicines. Then eventually these tumours become resistant against this therapy and what you see then is that other genes due to the fact that other genes are mutated or upregulated. The most common is actually PI3 kinase which is mutated but in a number of cases other genes are upregulated and one of these genes is, for instance, IRS4. Also that was a gene which we discovered with insertion mutagenesis recently.
What are the follow-up plans for these 30 genes?
A number of them we know how they plug in in the pathways, the pathways I have described, but for instance when we found these R-spondins, already ten years ago in fact, there was nothing known about R-spondins. So what we wanted to know is what are they doing. In the meantime that has been quite well established but there are other genes where we don’t know so much about them, so what pathway they are involved in. I can’t work on all these genes but probably then other people can see what genes they are like if they want to work on it but we worked on the IRS4 and also genes ERAS and R-spondins. So those are the three genes we are right now working on. You can’t work on thirty genes, that’s too much.
Do you have anything else to add?
R-spondins, as I said, they affect the stem cells. My talk will also be about LTR6 stem cells in breast cancer. It looks like that is a kind of stem cell in the breast; I said breast cancer, I should limit that to the breast for the time being. Maybe it’s quite likely there they might be also involved in cancer but we haven’t really definitely proven that. So that is one of the things we are still working on.