General Health

Cancer Driver Mutations, Cancer Mutagenesis

Mutations, which can be generated by errors in DNA replication, the impact of exogenous mutagens, or endogenous DNA damage, supply the raw material for natural selection in evolution. Mutations can harm the replication and genome maintenance machinery, or they can be changed by physiological circumstances and differential levels of expression in cancer.

According to Gao et al., the DNA-damage response (DDR) mechanism maintains the stability and integrity of the human genome. Unrepaired DNA damage is a primary source of carcinogenic mutations. When DNA repair is inadequate, DNA damage accumulates. Due to error-prone translesion synthesis, such excess DNA damage might exacerbate mutational mistakes during DNA replication. Excessive DNA damage can potentially cause epigenetic changes as a result of errors during DNA repair. Cancer can be caused by such mutations and epigenetic changes.

Epigenetic processes frequently suppress DDR genes in human cancer. Such repression might be caused by DNA methylation of promoter regions or by a microRNA suppression of DDR genes. In several kinds of cancer, epigenetic inhibition of DDR genes happens more frequently than gene mutation. Thus, epigenetic repression is frequently more significant than mutation in lowering DDR gene expression. This decreased expression of DDR genes is most likely a key cause of carcinogenesis.

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Analysis of mutational (mutable) DNA motifs (A DNA motif is defined as a nucleic acid sequence pattern that has some biological significance such as being DNA binding sites for a regulatory protein, i.e., a transcription factor) can be essential for understanding the mechanisms of mutagenesis in cancer. These patterns are the signatures of interactions between DNA and mutagens, as well as between DNA and repair/replication/modification enzymes. The AID motif WRCY/RGYW (W = A or T, R = purine, and Y = pyrimidine) with C to T/G/A mutations and error-prone DNA pol ascribed AID-related mutations (A to G/C/G) in WA/TW motifs are two examples of motifs.

Pooling all mutations from cancer samples, regardless of type or context, into a discrete distribution is one more method for analysing the reported mutational spectra and DNA sequence context of mutations in cancers. If there are several cancer samples, their context-dependent mutations can be displayed as a nonnegative matrix. This matrix can be further broken down into parts (mutational signatures), each of which ought to describe a specific mutagenic factor. This decomposition challenge has been addressed by several computational techniques.

The Sanger Institute Mutational Signature Framework includes a MATLAB package that first uses the Non-negative Matrix Factorization (NMF) approach. The DeconstructSigs R programme and MutaGene server, on the other hand, may offer the identification of contributions of various mutational signatures for a single tumour sample if mutations from a single tumour sample are the only ones that are known. Additionally, the MutaGene service offers background models and signatures for mutagens or cancer-specific mutations that may be used to estimate DNA and protein site mutability and separate the relative roles of mutagenesis and selection in the development of cancer.

Synthetic lethality

The concept of “collateral lethality” has enormous potential for discovering new and targeted treatment targets in oncology. In some malignancies, passenger genes that are close to tumour suppressor genes on the chromosome are collaterally eliminated. Finding redundant genes that perform essential cellular functions may be an untapped resource for later using a synthetic lethality strategy. Enolase 2 is mostly expressed in brain tissues and is encoded by the gene ENO2. Muller discovered that in GBM cells with homozygous ENO1 deletion, both genetic and pharmacological ENO2 inhibition results in a synthetic lethality outcome by selectively killing cells.

All cells, not just cancer cells, depend on certain oncogenes for survival. Drugs that kill these oncogenes may also harm healthy cells, leading to serious morbidity. Patients with cancer have a longer survival time thanks to therapies based on the synthetic lethality principle. One synthetic lethal method for cancers with or without DNA mismatch repair (MMR) abnormalities was examined in a human Phase II clinical trial. A stronger immune response is made possible by PD-1 gene inhibition. One of the top 12 carcinogenic mutations in the ARID1A mutation.

The individual knockout of each gene in a genome is an additional strategy that can be used to study the impact on both healthy and malignant cells. The system-wide suppression of the suppressed gene can kill cancerous cells while mostly sparing healthy ones if the knockout of an otherwise non-essential gene has little to no impact on healthy cells but is fatal to cancerous cells having a mutant oncogene. The method was used to find PARP-1 inhibitors for the treatment of malignancies linked to BRCA1/BRCA2. In this instance, only the malignant cells are killed when PARP-1 inhibition and BRCA gene mutations are present together.

References 

1.  https://pubmed.ncbi.nlm.nih.gov/28498882/

2.  https://pubmed.ncbi.nlm.nih.gov/26870836/

Author

 Yash Batra

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