Oxidative Distress Induces Wnt/β-Catenin Pathway Modulation in Colorectal Cancer Cells: Perspectives on APC Retained Functions

Colorectal cancer (CRC) is a multistep process that arises in the colic tissue microenvironment. Oxidative stress plays a role in mediating CRC cell survival and progression, as well as promoting resistance to therapies. CRC progression is associated with Wnt/β-Catenin signaling dysregulation and loss of proper APC functions. Cancer recurrence/relapse has been attributed to altered ROS levels, produced in a cancerous microenvironment. The effect of oxidative distress on Wnt/β-Catenin signaling in the light of APC functions is unclear. This study evaluated the effect of H₂O₂-induced short-term oxidative stress in HCT116, SW480 and SW620 cells with different phenotypes of APC and β-Catenin. The modulation and relationship of APC with characteristic molecules of Wnt/β-Catenin were assessed in gene and protein expression. Results indicated that CRC cells, even when deprived of growth factors, under acute oxidative distress conditions by H₂O₂ promote β-Catenin expression and modulate cytoplasmic APC protein. Furthermore, H₂O₂ induces differential gene expression depending on the cellular phenotype and leading to favor both Wnt/Catenin-dependent and -independent signaling. The exact mechanism by which oxidative distress can affect Wnt signaling functions will require further investigation to reveal new scenarios for the development of therapeutic approaches for CRC, in the light of the conserved functions of APC.

[Methylnitrosourea as challenge mutagen in assessment of the DNA mismatch repair (MMR) activity: association with some types of cancer]

Total repair capability is a widely used phenotypic marker of predisposition to cancer. Evaluation of this parameter implies using a challenge mutagen in an in vitro system to unmask latent genetic instability and repair insufficiency in the target cells. Traditionally, these investigations involve two tests, evaluation of mutagenic susceptibility (chromosomal aberrations) and genotoxic effect (DNA comet assay). The present study was focused on analysis of the effect of methylnitrosourea (MNU) on resting and PHA-stimulated lymphocytes from healthy donors and patients with gynecological cancer. Cytotoxic effect of MNU (apoptotic lymphocyte death) was estimated using two parameters, interaction of the cells with the annexin V-FITC complex, and morphological changes of the nuclei after their staining with the mixture of two DNA tropic dyes. The genotoxic effect of MNU, namely, secondary double-strand DNA breaks, was scored using the neutral comet assay, modified for the calculation of the comets produced exclusively by BrUdr-labeled proliferating lymphocytes. The proportion of these comets was represented as the proliferative cell index. It was shown that resting lymphocytes were resistant to genotoxic and cytotoxic effects of MNU. The response of proliferating cells to the action of MNU was expressed as the development of secondary DNA breaks (P <0.01), along with the increased frequency of apoptosis (P <0.05). The genotoxic effect of MNU on stimulated lymphocytes of gynecological cancer patients was fourfold lower compared to healthy donor lymphocytes. In response to the MNU action, patient lymphocytes did not change their proliferative index, while in healthy donor lymphocytes proliferative index was two times decreased in response to the MNU action. The data obtained pointed to the association between the cytotoxic response of the lymphocytes to the action of MNU and gynecological cancer. Since only proliferating lymphocytes response to the genotoxic effect of MNU, and the effect is revealed a day after the mutagen action, it is suggested that this phenomenon is associated with postreplicative repair, MMR, the substrate of which is O6-methylguanin. The MMR deficiency in patient lymphocytes determines their tolerance to the action of MNU. Genotoxic effect of lymphocytes to the action of MNU can serve as a marker of MMR, as well as of the MMR deficiency-associated gynecological cancer.