DNA polymeraseθ up-regulation is associated with poor survival in breast cancer, perturbs DNA replication, and promotes genetic instability

Abstract

"Replicative stress" is one of the main factors underlying neoplasia from its early stages. Genes involved in DNA synthesis may therefore represent an underexplored source of potential prognostic markers for cancer. To this aim, we generated gene expression profiles from two independent cohorts (France, n = 206; United Kingdom, n = 117) of patients with previously untreated primary breast cancers. We report here that among the 13 human nuclear DNA polymerase genes, DNA Polymerase θ (POLQ) is the only one significantly up-regulated in breast cancer compared with normal breast tissues. Importantly, POLQ up-regulation significantly correlates with poor clinical outcome (4.3-fold increased risk of death in patients with high POLQ expression), and this correlation is independent of Cyclin E expression or the number of positive nodes, which are currently considered as markers for poor outcome. POLQ expression provides thus an additional indicator for the survival outcome of patients with high Cyclin E tumor expression or high number of positive lymph nodes. Furthermore, to decipher the molecular consequences of POLQ up-regulation in breast cancer, we generated human MRC5-SV cell lines that stably overexpress POLQ. Strong POLQ expression was directly associated with defective DNA replication fork progression and chromosomal damage. Therefore, POLQ overexpression may be a promising genetic instability and prognostic marker for breast cancer.specialized DNA replication | prognosis marker | S-phase checkpoint B esides the "replicative" DNA polymerases POLA, POLD, and POLE, which are involved in conventional DNA replication of the undamaged genome, mammalian nuclei contain 10 additional specialized DNA polymerases that play a role in replication, repair, and recombination of damaged DNA (1, 2) and thus may be of paramount importance to preserve the integrity of the genome.Specialized DNA polymerases are frequently deregulated in neoplasia (3-10). Indeed, the intracellular balance between the error-free, replicative polymerases POLA, POLD, and POLE and the error-prone, specialized DNA polymerases (POLH, POLL, POLM, POLN, POLK, POLB, POLI, POLQ, POLZ/REV3L, and REV1) appears to be of great importance for the maintenance of genome stability (11)(12)(13)(14). Here, we wondered whether misregulation of DNA polymerases could be a signature of breast cancer progression. Indeed, beside the standard classification used by pathologists, there is a clear lack of tools to accurately predict the clinical outcome of many patients.We specifically measured the expression levels of the 13 human replicative and specialized DNA polymerases in 206 breast carcinomas. We report that, differently from the replicative and the other specialized DNA polymerases, POLQ was significantly upregulated in most of the breast tumors analyzed. Such up-regulation was associated with poor clinical outcome.POLQ is an error-prone, specialized DNA polymerase that might operate during "normal" genomic replication because it bypasses some endogenous DNA lesions an...

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

“…To obtain more insight into the mechanism by which Pol y contributes to replication timing, we analysed the impact of the excess of Pol y on replication timing at a genome-wide level. We generated human cells that stably overexpress Pol y compared with the endogenous Pol y level of the isogenic control 23 (Fig. 6a) and examined replication timing as described above.…”

“…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 .…”

A Polymerase Theta-dependent repair pathway suppresses extensive genomic instability at endogenous G4 DNA sites

“…We anticipate that ectopic activation of TMEJ may be of high clinical significance, also considering the recent finding that Polymerase Theta upregulation is associated with poor survival in cancer 35,36 ; if not properly controlled, POL y's ability to tie DNA ends together can have very undesirable effects, as it provides cells with the means to proliferate in the presence of increased replication stress 37 . Blocking this activity may thus constitute a potent strategy towards preventing cancerous growth.…”

Infiltrating Breast Carninomas Multifocality: Clinical and Biological Features

“…While some useful prognostic factors in these tumors are clinically well established [1][2][3][4][5][6][7], less known and controversy is the multifocality, which is not always well defined from a conceptual point of view [8][9] and often analyzed and associated with multicentricity. Also, tumor size is still under discussion [10] which one considered, the larger lesion or the sum of all lesions; it seems that the first option shown has superior clinical utility [11][12].…”