Increased prevalence of hybrid epithelial/mesenchymal state and enhanced phenotypic heterogeneity in basal breast cancer

The epipliancy journey: Tumor initiation at the mercy of identity crisis and epigenetic drift

Cellular pliancy refers to the unique disposition of different stages of cellular differentiation to transform when exposed to specific oncogenic insults. This concept highlights a strong interconnection between cellular identity and tumorigenesis, and implies overcoming of epigenetic barriers defining cellular states. Emerging evidence suggests that the cell-type-specific response to intrinsic and extrinsic stresses is modulated by accessibility to certain areas of the genome. Understanding the interplay between epigenetic mechanisms, cellular differentiation, and oncogenic insults is crucial for deciphering the complex nature of tumorigenesis and developing targeted therapies. Hence, cellular pliancy relies on a dynamic cooperation between the cellular identity and the cellular context through epigenetic control, including the reactivation of cellular mechanisms, such as epithelial-to-mesenchymal transition (EMT). Such mechanisms and pathways confer plasticity to the cell allowing it to adapt to a hostile environment in a context of tumor initiation, thus changing its cellular identity. Indeed, growing evidence suggests that cancer is a disease of cell identity crisis, whereby differentiated cells lose their defined identity and gain progenitor characteristics. The loss of cell fate commitment is a central feature of tumorigenesis and appears to be a prerequisite for neoplastic transformation. In this context, EMT-inducing transcription factors (EMT-TFs) cooperate with mitogenic oncoproteins to foster malignant transformation. The aberrant activation of EMT-TFs plays an active role in tumor initiation by alleviating key oncosuppressive mechanisms and by endowing cancer cells with stem cell-like properties, including the ability to self-renew, thus changing the course of tumorigenesis. This highly dynamic phenotypic change occurs concomitantly to major epigenome reorganization, a key component of cell differentiation and cancer cell plasticity regulation. The concept of pliancy was initially proposed to address a fundamental question in cancer biology: why are some cells more likely to become cancerous in response to specific oncogenic events at particular developmental stages? We propose the concept of epipliancy, whereby a difference in epigenetic configuration leads to malignant transformation following an oncogenic insult. Here, we present recent studies furthering our understanding of how the epigenetic landscape may impact the modulation of cellular pliancy during early stages of cancer initiation.

Recurring cycles of deprivation of serum and migration in confined spaces augments ganglioside SSEA-4 expression, boosting clonogenicity and cisplatin resistance in TNBC cell line

The remarkable biophysical properties of metastatic migrating cells, such as their exceptional motility and deformability, enable them to migrate through physical confinements created by neighboring cells or extracellular matrix. This study explores the adaptive responses of breast cancer (BC) cell sublines derived from the highly aggressive, metastatic triple-negative MDA-MB-231 and the non-metastatic MCF7 human BC cell lines, after undergoing three rounds of confined migration (CM) stress. Our findings demonstrate that CM elicits common and cell-type specific adaptive responses in BC cell sublines. In particular, both cell sublines exhibit a similar enhancement of clonogenicity and nanoparticle (NP) uptake activity, indicating tumorigenic potential. We have, for the first time, shown that stimulation with CM induces a hybrid epithelial-to-mesenchymal transition (EMT) phenotype of MDA-MB-231 cells. This transition is characterized by a significant rise in the expression of stage-specific embryonic antigen-4 (SSEA4), alongside a substantial decline in the population of CD133+ cells and a marked reduction in Ki67 expression in the MDA-MB-231-derived subline following Cis-Platin treatment. These changes are likely associated with heightened resistance of this subline to cisplatin. In contrast, CM induces far fewer such alterations in the MCF7-derived counterpart with a notable increase of CD133+ population, which seems to be insufficient to change cell susceptibility to cisplatin exposure. This study contributes to our understanding of the adaptive mechanisms underlying metastasis and drug resistance in breast cancer, emphasizing the need for personalized approaches in cancer treatment that consider the heterogeneous responses of different cancer subtypes to environmental stresses.

The Clinical Relevance of Epithelial-to-Mesenchymal Transition Hallmarks: A Cut-Off-Based Approach in Healthy and Cancerous Cell Lines

The atypical activation of the epithelial-to-mesenchymal transition represents one of the main mechanisms driving cancer cell dissemination. It enables epithelial cancer cells to detach from the primary tumor mass and gain survival advantages in the bloodstream, significantly contributing to the spread of circulating tumor cells. Notably, epithelial-to-mesenchymal transition is not a binary process but rather leads to the formation of a wide range of cell subpopulations characterized by the simultaneous expression of both epithelial and mesenchymal markers. Therefore, analyzing the modulation of EMT hallmarks during the conversion from healthy cells to metastatic cancer cells, which acquire stem mesenchymal characteristics, is of particular interest. This study investigates the expression of a panel of epithelial-to-mesenchymal transition-related genes in healthy cells, primary and metastatic cancer cells, and in mesenchymal cell lines, derived from various tissues, including the lung, colon, pancreas, skin, and neuro-ectoderm, with the aim of identifying potential cut-off values for assessing cancer aggressiveness. Interestingly, we found that the expression levels of CDH1, which encodes the epithelial marker E-cadherin, CDH5, encoding vascular endothelial cadherin, and the epithelial-to-mesenchymal transition-transcription factor ZEB1, effectively distinguished primary from metastatic cancer cells. Additionally, our data suggest a tissue-specific signature in the modulation of epithelial-to-mesenchymal transition markers during cancer progression. Overall, our results underscore the importance of investigating epithelial-to-mesenchymal transition as a tissue-specific process to identify the most suitable markers acting as potential indicators of disease aggressiveness and therapeutic responsiveness.

GABA Type A receptors expressed in triple negative breast cancer cells mediate chloride ion flux

Triple negative breast cancer (TNBC) is known for its heterogeneous nature and aggressive onset, limited unresponsiveness to hormone therapies and immunotherapy as well as high likelihood of metastasis and recurrence. Since no targeted standard treatment options are available for TNBC, novel and effective therapeutic targets are urgently needed. Ion channels have emerged as possible novel therapeutic candidates for cancer therapy. We previously showed that GABAA β3 subunit are expressed at higher levels in TNBC cell lines than non-tumorigenic MCF10A cells. GABAA β3 subunit knockdown causes cell cycle arrest in TNBC cell lines via decreased cyclin D1 and increased p21 expression. However, it is not known if the upregulated GABAAR express at the cell-surface in TNBC and mediate Cl- flux. Cl- ions are known to play a role in cell-cycle progression in other cancers such as gastric cancer. Here, using surface biotinylation and (N-(Ethoxycarbonylmethyl)-6-Methoxyquinolinium Bromide) MQAE-dye based fluorescence quenching, we show that upregulated GABAAR are on the cell-surface in TNBC cell lines and mediate significantly higher chloride (Cl-) flux as compared to non-tumorigenic MCF10A cells. Moreover, this GABAAR mediated Cl- flux can be modulated by pharmacological agents and is decreased in TNBC cells with GABAA β3 subunit knockdown. Further, treatment of TNBC cells with bicuculline, a GABAAR antagonist reduced cell viability in TNBC cells Overall, these results point to an unexplored role of GABAAR mediated Cl- flux in TNBC.

Prognostic Significance of Combining Cytokeratin-19, E-Cadherin and Ki-67 Analysis in Triple-Negative Breast Cancer with Basal-Like and Non-Basal-Like Phenotype

Triple-negative breast cancer (TNBC) is known to have the worst outcome compared to the other forms of breast cancer. Moreover, molecular markers identified basal-like breast cancer (BLBC) phenotypes to be also related to a worse prognosis. In this study, we evaluated by immunohistochemistry (IHC) the prognostic significance of combining Cytokeratin-19 (CK19), E-cadherin, and Ki-67 tissue expression in triple-negative breast cancer (TNBC) cases presenting a basal-like (BLBC) or a non-basal-like (n-BLBC) phenotype to improve the selection and the monitoring of BC patients with a more aggressive outcome. Herein, when compared to n-BLBC, patients with BLBC showed a positive correlation with lymph node metastasis occurrence and lower survival rates. Immunohistochemistry analysis revealed significantly lower E-cadherin prevalence and higher prevalence of both CK19 and Ki-67 in BLBC when compared to n-BLBC. Spearman correlation showed that E-cadherin is negatively and significantly correlated to CK19 and Ki-67 expressions. Moreover, in BLBC, expressing both CK19 and Ki-67 combined with E-cadherin loss was associated with the worst relapse-free and overall survival. In conclusion, TNBC/BLBC phenotypes simultaneously losing E-cadherin and overexpressing CK19 and Ki-67 markers are the most aggressive forms. This combined analysis could be a predictive marker of poor prognosis.