The unconventional pathway of DNA double-strand break repair

Avani Dave, Jai Hind College

Breast cancer gene BRCA1 has marked its presence as a protein mostly known for being an active contributor in the hereditary associated breast cancer. Apart from being the villain, BRCA1 also plays an indispensable role in the cellular machinery that works towards repairing the double-strand DNA breakage. Recently, researchers from Japan set their foot for the discovery of a novel technique that is incorporated by the cells in order to secure these snipped DNA ends confirming an efficient restoration of the features after successfully repairing it.

A recent study conducted by Isobe, S.Y., et al. (A group of researchers from Osaka University) was published in Cell Reports. The findings from the study demonstrated that there is an active binding of protein phosphatase 1 (PP1) on the region of the broken double-stranded DNA at an initial stage of recognition. Thereby enhancing the repair process by a mechanism known as nonhomologous end-joining instead of the homologous recombination technique.

The Study:

The cell uses several categorical decision-making breakdowns to determine the most up-to-the-mark pathway for repairing the double-strand breaks. The selection of the pathway needs to be critically regulated. One of the several existing methods makes use of a protein called RIF1 that binds to the chipped DNA ends, such that the binding of this protein wards off attachment of other proteins that might further degrade the break site to bring about repairing of this site by homologous recombination.

The first author of this study, Shin-ya Isobe explained how the double-strand breaks which have not been safeguarded by the binding of the RIF1 protein complex stand more susceptible to undergo digestion by other proteins. The result of this digestion of the DNA breaks leads to the formation of a fragment of single-stranded DNA which can further be subjected to undergo repair by the homologous recombination method. He added how this successive digestion could be avoided with the help of a protein known as Shieldin. It has been observed that Shieldin undergoes binding to the single-stranded DNA tail via collaboratively binding to the RIF1. That being said, it is also conjectured that there are several other contributing factors that are centrally essential for this process but are unidentified due to insufficient research. 

This makes the further identification of these contributing factors known to assist in safeguarding the new breaks in the DNA ends a critical focal point of the research. To cater to this requirement the researchers utilized a mechanism known as proteomic mass spectrometry so as to determine the interaction of several proteins with the RIF1 and their potential role in repair. 

Results obtained from the study:

It was observed that the specific binding of the PP1 to RIF1 occurs at the site of DNA breakage. This mutual physical interaction is of utmost importance in order to bring about accurate shielding from the other proteins that convert these broken ends to a single-stranded DNA for further treatment. To put the point in place, it can be said that this interaction between the two proteins avoids the formation of the single-stranded tail. The single-stranded tail usually traces the path of homologous recombination. If the desired mechanistic pathway is that of non-homologous end joining, then it needs an early response from PP1, before the Shieldin protein starts redirecting the repair pathway. This novel mechanism was delineated as an outcome of this study, highlighting the selection of a double-stranded repair system. 

Significance of the study:

The critical features of several cancers include errors in the double-strand break repair mechanisms. Hence, detailed identification of the underlying principle of how a particular cell selects the most efficient pathway is needed. This will allow us to comprehend the mechanism that is incorporated to rectify these damaged sites, shedding some light on the arena of cancer development. The findings of this study,  therefore, opens a new door for the development of novel treatment options for hereditary-mediated breast and ovarian cancer in the coming years.

Reference:

1. Isobe, S.Y., Hiraga, S., Nagao, K., et al. (2021). Protein phosphatase 1 acts as a RIF1 effector to suppress DSB resection prior to Shieldin action. Cell Reports, 36(2), 109383. https://doi.org/10.1016/J.CELREP.2021.109383

Author info:

Avani Dave is currently in the final year of her bachelor’s degree, majoring in Life Sciences. Holding a good academic and extra-curricular record, she is on a constant journey of acquiring exposure in her field of interest while simultaneously not limiting herself to just that. Avani likes studying Diseases and Syndromes and everything under this umbrella! That being said, she is adept at working across departments and promises to deliver.

LinkedIn – https://www.linkedin.com/avani-dave/

Publications in BioXone:

1. Dave, A. (2021). ECMO: An artificial heart-lung set for COVID-19 treatment. BioXone. https://bioxone.in/news/worldnews/ecmo-an-artificial-heart-lung-set-for-covid-19-treatment/
2. Dave, A. (2021). Ultrasound-on-chip: a novel platform for medical imaging. https://bioxone.in/news/worldnews/ultrasound-on-chip-a-novel-platform-for-medical-imaging/