The Mechanism and Prognostic Value of DNA Polymerase δ Subunits in Hepatocellular Carcinoma: Implications for Precision Therapy

Altered immunoexpression of DNA polymerase delta 1 catalytic subunit (POLD1) in colorectal cancer

Introduction

The study aimed to determine the immunoexpression levels of polymerase delta 1 catalytic subunit (POLD1), a catalytic and proofreading subunit of DNA polymerase delta, in the sections of colorectal cancer (CRC), and to evaluate the significance of POLD1 as a potential prognostic factor in CRC.

Material and methods

Paired, tumour and non-cancerous tissue samples of the large intestine distant to the neoplasm were collected from the postoperative material of 78 patients who underwent surgical resection of CRC tumours. Polymerase delta 1 catalytic subunit protein levels were determined using immunohistochemistry. Clinical, pathomorphological, and survival data of the patients were pooled. In addition, POLD1 mRNA expression levels of 599 CRC patients were extracted from The Cancer Genome Atlas (TCGA) datasets and subjected to statistical and survival analysis including the Kaplan-Meier method followed by the log-rank test.

Results

Immunoexpression of POLD1 was found in the nuclei of the tumour cells and epithelial cells of unchanged intestinal mucosa. Polymerase delta 1 catalytic subunit immunoreactivity in the tumour was heterogenous, and the average immunoreactivity score was decreased in cancer cells when compared to the mucosa of matched sections of unchanged large intestine (p = 0.0259). However, POLD1 expression at the protein and mRNA levels did not associate with clinicopathological characteristics of the patients and their survival.

Conclusions

Despite previous studies suggesting that POLD1 genetic alterations could be promising molecular biomarkers in CRC, our results do not support any prognostic significance of POLD1 expression in CRC.

Characterization of DNA Polymerase Genes in Amazonian Amerindian Populations

Due to their continuing geographic isolation, the Amerindian populations of the Brazilian Amazon present a different genetic profile when compared to other continental populations. Few studies have investigated genetic variants present in these populations, especially in the context of next-generation sequencing. Knowledge of the molecular profile of a population is one of the bases for inferences about human evolutionary history, in addition, it has the ability to assist in the validation of molecular biomarkers of susceptibility to complex and rare diseases, and in the improvement of specific precision medicine protocols applied to these populations and to populations with high Amerindian ancestry, such as Brazilians. DNA polymerases play essential roles in DNA replication, repair, recombination, or damage repair, and their influence on various clinical phenotypes has been demonstrated in the specialized literature. Thus, the aim of this study is to characterize the molecular profile of POLA1, POLE, POLG, POLQ, and REV3L genes in Amerindian populations from the Brazilian Amazon, comparing these findings with genomic data from five continental populations described in the gnomAD database, and with data from the Brazilian population described in ABraOM. We performed the whole exome sequencing (WES) of 63 Indigenous individuals. Our study described for the first time the allele frequency of 45 variants already described in the other continental populations, but never before described in the investigated Amerindian populations. Our results also describe eight unique variants of the investigated Amerindians populations, with predictions of moderate, modifier and high clinical impact. Our findings demonstrate the unique genetic profile of the Indigenous population of the Brazilian Amazon, reinforcing the need for further studies on these populations, and may contribute to the creation of public policies that optimize not only the quality of life of this population, but also of the Brazilian population.