New Mechanism for Precise Protein Production Unveiled

A new process that is essential to the synthesis of cellular proteins has been discovered by an international research team. The process known as splicing causes the cell's protein-making blueprints to be incorrectly altered when this system is interfered with.

The research, which was headed by Goethe University Frankfurt, clarifies how some mutations could cause retinitis pigmentosa, a retinal condition. Crucially, these discoveries may also pave the way for novel diagnostic procedures and therapies for a variety of other illnesses, such as Parkinson's, Alzheimer's, and some types of cancer.

The fundamental building blocks of life are found in genes, which tell cells which amino acids to put together in what order to make particular proteins. Approximately 20,000 of these instructions are encoded in the human genome.

“Nevertheless, our cells can produce several hundred thousand different proteins,” explained Professor Ivan Đikić from the Institute of Biochemistry II at Goethe University Frankfurt.

This “splicing” mechanism makes this diversity possible. A copy of the pertinent instructions is created in the cell nucleus when a protein is needed. This transcript is altered during splicing when specific portions are eliminated by the spliceosome, a cellular editing complex. This results in different blueprints for different proteins, depending on which sections are left out.

Splicing Accuracy Enhanced

The cell's ability to survive depends on this mechanism.

The spliceosome is composed of multiple components that secure the production of functional proteins controlling cellular life. If this complex is disrupted, it can lead to the death of the affected cell. For this reason, spliceosome inhibitors are considered as potential anti-cancer drugs.”

Ivan Đikić, Professor, Institute of Biochemistry II, Goethe University Frankfurt

The drawback of any spliceosome inhibitor identified to date is that total inhibition of this “editing office” also impacts healthy cells, leading to serious adverse effects.

Researchers have now discovered a technique that more subtly disrupts the splicing process in an international investigation headed by Goethe University. It is associated with a particular region of the spliceosome, which is made up of three subunits called U4/U6.U5.

We already knew that certain mutations in these subunits are linked to the eye disease retinitis pigmentosa. What we did not yet understand was the exact impact of these mutations.”

Dr. Cristian Prieto-Garcia, Study First Author, Institute of Biochemistry II, Goethe University Frankfurt

Experiments on Zebrafish Combined with Mathematical Calculations

The team has now successfully closed this information gap in zebrafish experiments. According to their research, a protein known as USP39 typically stabilizes the spliceosome subunits U4, U5, and U6 as a complex.

However, the tripartite complex's stability is weakened and the spliceosome loses its precision when subunits are altered or USP39 is missing. After a transcript has been chopped, U4/U6.U5 often guarantees the prompt and proper re-joining of loose ends during splicing. This re-joining is delayed in the absence of USP39 or when subunits are altered.

“This increases the likelihood of incorrect connections, as we were able to show in computer simulations,” explained Prieto-Garcia.

As a result, the cell creates defective proteins based on transcripts that have been wrongly altered. Within the cell, they can build up and create aggregates. The protective mechanism that cells have in place to eliminate faulty molecules was triggered in cells that lacked USP39. But eventually, the protein clumps overpowered this “garbage disposal,” causing the zebrafish retina's cells to die.

Surprising Discovery

The discovery of this mechanism was unexpected. We suspect it may also explain why retinal cells in retinitis pigmentosa patients die. Defective splicing variants might also play a role in the development of neurodegenerative diseases like Alzheimer’s or Parkinson’s. On the other hand, this mechanism may be targeted by new therapeutic approaches for types of cancer that are highly dependent on the correct function of the spliceosome.”

Ivan Đikić, Professor, Institute of Biochemistry II, Goethe University Frankfurt

With their fast rate of division, certain extremely aggressive tumors generate high levels of USP39 and associated splicing factors: They need extremely accurate splicing, which USP39 performs, to sustain steady protein production.

Đikić explained, “Blocking USP39 in these cancer cells could selectively kill them. Healthy cells, on the other hand, with their much lower division activity, would be spared. This is an approach that we are currently investigating.”