DNA replication stress response involving PLK1, CDC6, POLQ, RAD51 and CLASPIN upregulation prognoses the outcome of early/mid-stage non-small cell lung cancer patients

Abstract

Lung cancer is the leading cause of cancer deaths worldwide. Clinical staging classification is generally insufficient to provide a reliable prognosis, particularly for early stages. In addition, prognostic factors are therefore needed to better forecast life expectancy and optimize adjuvant therapeutic strategy. Recent evidence indicates that alterations of the DNA replication program contribute to neoplasia from its early stages and that cancer cells are frequently exposed to endogenous replication stress. We therefore hypothesized that genes involved in the replication stress response may represent an under-explored source of biomarkers. Expressions of 77 DNA replication-associated genes implicated in different aspects of chromosomal DNA replication, including licensing, firing of origins, elongation, replication fork maintenance and recovery, lesion bypass and post-replicative repair were determined in primary tumors and adjacent normal tissues from 93 patients suffering from early- or mid-stage non-small cell lung cancer (NSCLC). We then investigated a statistically significant interaction between gene expressions and survival of early-stage NSCLC patients.The expression of five genes, that is, POLQ, PLK1, RAD51, CLASPIN and CDC6 was associated with overall, disease-free and relapse-free survival. The expression levels are independent of treatment and stage classification. Except RAD51, their prognostic role on survival persists after adjustment on age, sex, treatment, stage classification and conventional proliferation markers, with a hazard ratio of 36.3 for POLQ (95%CI 2.6–517.4, P=0.008), 23.5 for PLK1 (95%CI 1.9–288.4, P=0.01), 20.7 for CLASPIN (95%CI 1.5–275.9, P=0.02) and 18.5 for CDC6 (95%CI 1.3–267.4, P=0.03). We also show that a five-gene signature including POLQ, PLK1, RAD51, CLASPIN and CDC6 separates patients into low- and high-risk groups, with a hazard ratio of 14.3 (95% CI 5.1–40.3, P<0.001). This ‘replication stress' metamarker may be a reliable predictor of survival for NSCLC, and may also help understand the molecular mechanisms underlying tumor progression.

A role for DNA polymerase θ in the timing of DNA replication

“…This novel Pol y function may be particularly important within the context of cancer, as high POLQ expression is strongly associated with poor clinical outcome of patients with colon, breast and lung cancers [22][23][24]55,56 . Abnormal temporal control of replication, recently demonstrated in several haematologic malignancies, has been proposed to represent a common mechanism responsible for genomic instability found in cancer cells 57 ; therefore, Pol y overexpression may be of cardinal importance in defining the modified temporal replication programme in cancer cells and may constitute a driving force for chromosomal instability [58][59][60] .…”

“…By conducting large-scale studies of the expression of DNA replication factors in patients with colon, breast and lung cancer, we recently uncovered major alterations in the expression pattern of POLQ, the gene encoding Pol y, and discovered that excess POLQ correlates with genetic instability and poor prognosis [22][23][24] . This is, to our knowledge, the strongest link between a negative clinical outcome and the expression of a DNA polymerase 25 .…”

Excess Polθ functions in response to replicative stress in homologous recombination-proficient cancer cells

“…We and others have demonstrated that Polθ expression is a strong prognostic factor in different types of cancers (Allera-Moreau et al, 2012; Lemée et al, 2010; Pillaire et al, 2010). Recent studies have demonstrated the important role of Polθ in DNA repair under stress conditions and suggest that Polθ overexpression may play a key role in mechanisms of protection against genotoxic therapies (Yousefzadeh et al, 2014), especially when other repair pathways are no longer functional (Ceccaldi et al, 2015; Mateos-Gomez et al, 2015).…”

“…To explore whether POLQ deregulation in cancer could be part of a global deregulation of genes involved in the response of replicative stress, we thought to go back to our previously reported real-time PCR data related to DNA samples from breast, colorectal or lung cancer patients (Allera-Moreau et al, 2012; Lemée et al, 2010; Pillaire et al, 2010), and address whether the expression of POLQ was correlated with the expression of other genes. By using Pearson coefficient of correlation with a threshold of P =0.65, we searched for genes that significantly correlated with POLQ expression.…”

“…(A) A Pearson’s test was used to compare POLQ mRNA expression and expression of any other analysed gene within each cohort. The number of patients analysed for lung, breast and colorectal cancer was 103, 221, and 52, respectively (Lemée et al, 2010; Pillaire et al, 2010; Allera-Moreau et al, 2012). A coefficient superior to 0.65 was considered associated to a positive correlation.…”