FLC in almost all patients is caused by a mutation that removes a particular stretch of DNA. As a result, tumor cells make a new unnatural protein composed of parts of two other proteins. It is not clear how the fusion protein causes FLC. One way to help find out is to force cells to make the fusion protein, and measure various kinds of changes in such cells.
In this paper they started with a cell line derived from the liver that had been made immortal by expressing a different fragments of an adeno virus, including a mutant version something called the SV40 large T antigen of liver. These cells, called HEK293 cells, in this paper were engineered to expressed the fusion protein DNAJB1-PRKACA, which drives FLC.. Comparing a large collection of proteins in cells with or without the fusion, numerous proteins were found to change in amount. Mitochondrial proteins or regulators were among these. The mitochondria are the power source of cells, and changes of these can have deleterious effects. Mitochondria in cells are constantly fusing and breaking apart. In confirmation that their dynamics are different in FLC, HEK 293 with the fusion protein had a higher rate of mitochondria breaking part. The investigators also compared RNAs, in the cells. Cells contain several classes of RNAs. One type instructs cells to make specific proteins, called coding RNAs. Another type is designated LINCs, which stands for long non-coding RNA. LINCs have been found to have multiple functions, including altering chromosome structure and turning genes on or off. A large change was found in the level of LINC00473, and that change is mimicked in FLC tumor cells, suggesting it is a genuine change, not just one that happens in the HEK293 cell experimental system. That may make measuring LINC00473 useful in diagnosis and in understanding how the fusion protein causes FLC.
—Written by Dr. Phil Coffino