A new biological mechanism explains how the same mutation can impair protein function at birth but also later lead to overactivation of the same protein and cancer
A study conducted at the University of Haifa, in collaboration with Rambam Health Care Campus, and published in the journal Disease Models & Mechanisms, explains how a single change in the RET gene can lead to two completely different diseases: a congenital defect in the digestive system that appears at birth, and a particular type of cancer (MEN2A) that develops later in life, usually at the thyroid. Because these are two biologically opposing conditions, it has not been clear until now how they can arise from the same mutation. “Our study provides an explanation that connects two medical conditions that seemed paradoxically opposite to each other, and shows how they are caused by the same biological process. This understanding reinforces the realization that genetic diseases are not fixed processes, but rather can evolve over the course of life depending on how the protein functions within cells,” explained Dr. Anna Fassler Bakhman from the University of Haifa, who led the study as part of her doctoral work.
In the study, the researchers focused on the RET gene, which encodes a central protein within cells that is involved in regulating growth, differentiation, and survival of cells in various tissues in the body. This protein is active, among other places, in the enteric nervous system and in the thyroid gland. Mutations in this gene have long been known to be associated with two completely different diseases: one is Hirschsprung’s disease, characterized by a congenital defect in the digestive system in which nerve cells are absent in the intestine, thereby impairing its normal function; the other is hereditary thyroid cancer of the MEN2A type. In the current study, Dr. Fassler Bakhman, Prof. Mickey Kosloff from the Department of Human Biology at the University of Haifa, Dr. Michal Cohen from Rambam Health Care Campus, and Prof. Rachel Kolodny from the Department of Computer Science at the University of Haifa, sought to examine how it is possible that certain mutations in the same gene lead to both phenomena – impairment (loss) of protein function and protein overactivation (gain of function), and to identify the biological mechanism that explains the connection between the conditions.
To decipher the mechanisms leading to the two diseases, the researchers built an extensive database including 77 different sites in the RET protein in which disease-associated mutations have been identified. This is the most comprehensive dataset collected to date for this protein and these diseases. The researchers analyzed the three-dimensional structure of the protein and examined how each genetic change affects its stability and its interactions with other proteins. As a central part of the study, the researchers used artificial intelligence-based methods to simulate with high precision the 3D structure of the protein and the way it forms connections with additional copies of itself. The combination of structural analysis and computational tools enabled the researchers to identify clear patterns and understand how different mutations lead either to loss of function, or to overactivation of the protein, or both.
A previous study conducted in Prof. Kosloff’s laboratory, published about a month ago in the journal BBA Advances, used similar computational tools to understand how a mutation in the GNAO1 gene causes a rare congenital neurological disease. In that study, too, the researchers found that the mutation caused loss of function of the protein. However, the molecular mechanism was completely different, since the mutation caused a loss of the ability of a molecular switch to activate processes within the brain. Nevertheless, the innovative approaches used by the researchers were parallel, and the results of both studies may help physicians understand how these genetic diseases can be treated.
The results of the current study indicate that in most cases of Hirschsprung’s disease, where nerve cells are absent in the intestine, the mutations impair the stability of the RET protein and therefore it cannot function properly. In these situations, the protein does not maintain its proper structure and fails to carry out its role in the development of the enteric nervous system. In contrast, in most cases of MEN2A-type cancers, the mutation leads to a specific amino acid that cannot form its usual connections within the RET protein. This amino acid, known as an “orphan cysteine”, can lead to two RET proteins to connect to each other abnormally, thereby causing RET self-activation without external regulation. The researchers found that in those mutations that cause both diseases together, the two conditions occur simultaneously: both impairment of protein stability and the formation of an “orphan cysteine” that leads to overactivation and cancer. “In other words, the same genetic change does not act similarly in different ages, but rather acts differently over the course of life, depending on the biological context”, the researchers explain. “In early stages it impairs the normal development of tissues, whereas in later stages it activates growth mechanisms in an uncontrolled manner. This understanding indicates that we need to work on more precise treatments tailored to both the type of mutation and the stage of life at which the disease manifests,” the researchers concluded.