Stochastic epithelial-mesenchymal transitions diversify non-cancerous lung cell behaviours

Epithelial-mesenchymal plasticity (EMP) is a hallmark of cancer. By enabling cells to shift between different morphological and functional states, EMP promotes invasion, metastasis and therapy resistance. We report that near-diploid non-cancerous human epithelial lung cells spontaneously shift along the EMP spectrum without genetic changes. Strikingly, more than half of single cell-derived clones adopt a mesenchymal morphology. We independently characterise epithelial-like and mesenchymal-like clones. Mesenchymal clones lose epithelial markers, display larger cell aspect ratios and lower motility, with mostly unaltered proliferation rates. Stemness marker expression and metabolic rewiring diverge independently of phenotypes. In 3D culture, more epithelial clones become mesenchymal-like. Thus, non-cancerous epithelial cells may acquire cancer metastasis-associated features prior to genetic alterations and cancerous transformation.

The synergy between miR-486-5p and tamoxifen causes profound cell death of tamoxifen-resistant breast cancer cells

Breast cancer (BC) is the most common type of malignancy in women. A subset of breast cancers show resistance to endocrine-based therapies. The estrogen receptor (ER) plays a critical role in developing hormone-dependent BC. Loss of ER contributes to resistance to tamoxifen therapy and may contribute to mortality. Thus, it is crucial to overcome this problem. Here, using luciferase reporter assays, qRT-PCR, and Western blot analyses, we demonstrate that the microRNA miR-486-5p targets HMGA1 mRNA, decreasing its mRNA and protein levels in ER-positive (ER+) BC cells. Consistently, miR-486-5p is significantly downregulated, whereas HMGA1 is considerably upregulated in ER+ BC samples. Remarkably, while both miR-486-5p and tamoxifen individually cause G2/M cell cycle arrest, combination treatment synergistically causes profound cell death, specifically in tamoxifen-resistant ER+ cells but not in tamoxifen-sensitive ER+ cells. Combined treatment with miR-486-5p and tamoxifen also additively reduces cell migration, invasion, colony formation, mammary spheroid formation and a CD24^-CD44⁺ cell population, representing decreased cancer stemness. However, these phenomena are independent of the tamoxifen responsiveness of the ER+ BC cells. Thus, miR-486-5p and tamoxifen exhibit additive and synergistic tumor-suppressive effects, most importantly causing profound cell death specifically in tamoxifen-resistant BC cells. Therefore, our work suggests that combining miR-486-5p replacement therapy with tamoxifen treatment is a promising strategy to treat endocrine therapy-resistant BC.

Multi-Omics Characterization of the Spontaneous Mesenchymal-Epithelial Transition in the PMC42 Breast Cancer Cell Lines

Epithelial–mesenchymal plasticity (EMP), encompassing epithelial–mesenchymal transition (EMT) and mesenchymal–epithelial transition (MET), are considered critical events for cancer metastasis. We investigated chromosomal heterogeneity and chromosomal instability (CIN) profiles of two sister PMC42 breast cancer (BC) cell lines to assess the relationship between their karyotypes and EMP phenotypic plasticity. Karyotyping by GTG banding and exome sequencing were aligned with SWATH quantitative proteomics and existing RNA-sequencing data from the two PMC42 cell lines; the mesenchymal, parental PMC42-ET cell line and the spontaneously epithelially shifted PMC42-LA daughter cell line. These morphologically distinct PMC42 cell lines were also compared with five other BC cell lines (MDA-MB-231, SUM-159, T47D, MCF-7 and MDA-MB-468) for their expression of EMP and cell surface markers, and stemness and metabolic profiles. The findings suggest that the epithelially shifted cell line has a significantly altered ploidy of chromosomes 3 and 13, which is reflected in their transcriptomic and proteomic expression profiles. Loss of the TGFβR2 gene from chromosome 3 in the epithelial daughter cell line inhibits its EMT induction by TGF-β stimulus. Thus, integrative ‘omics’ characterization established that the PMC42 system is a relevant MET model and provides insights into the regulation of phenotypic plasticity in breast cancer.

CEP55 is a determinant of cell fate during perturbed mitosis in breast cancer

The centrosomal protein, CEP55, is a key regulator of cytokinesis, and its overexpression is linked to genomic instability, a hallmark of cancer. However, the mechanism by which it mediates genomic instability remains elusive. Here, we showed that CEP55 overexpression/knockdown impacts survival of aneuploid cells. Loss of CEP55 sensitizes breast cancer cells to anti‐mitotic agents through premature CDK1/cyclin B activation and CDK1 caspase‐dependent mitotic cell death. Further, we showed that CEP55 is a downstream effector of the MEK1/2‐MYC axis. Blocking MEK1/2‐PLK1 signaling therefore reduced outgrowth of basal‐like syngeneic and human breast tumors in in vivo models. In conclusion, high CEP55 levels dictate cell fate during perturbed mitosis. Forced mitotic cell death by blocking MEK1/2‐PLK1 represents a potential therapeutic strategy for MYC‐CEP55‐dependent basal‐like, triple‐negative breast cancers.

Abstract P1-04-02: Not presented

This abstract was not presented at the conference.

Citation Format: Lin C-Y, Hazar-Rethinam M, Thangavelu P, Dray E, Duijf PH. Not presented [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-04-02.

MicroRNAs in cancer drug resistance: Basic evidence and clinical applications

Development of drug resistance has considerably limited the efficacy of cancer treatments, including chemotherapy and targeted therapies. Hence, understanding the molecular mechanisms underpinning the innate or the acquired resistance to these therapies is critical to improve drug efficiency and clinical outcomes. Several studies have implicated microRNAs (miRNA) in this process. MiRNAs repress gene expression by specific binding to complementary sequences in the 3' region of target messenger RNAs (mRNAs), followed by target mRNA degradation or blocked translation. By targeting molecules specific to a particular pathway within tumor cells, the new generation of cancer treatment strategies has shown significant advantages over conventional chemotherapy. However, the long-term efficacy of targeted therapies often remains poor, because tumor cells develop resistance to such therapeutics. Targeted therapies often involve monoclonal antibodies (mAbs), such as those blocking the ErB/HER tyrosine kinases, epidermal growth factor receptor (cetuximab) and HER2 (trastuzumab), and those inhibiting vascular endothelial growth factor receptor signaling (e.g., bevacizumab). Even though these are among the most used agents in tumor medicine, clinical response to these drugs is reduced due to the emergence of drug resistance as a result of toxic effects in the tumor microenvironment. Research on different types of human cancers has revealed that aberrant expression of miRNAs promotes resistance to the aforementioned drugs. In this study, we review the mechanisms of tumor cell resistance to mAb therapies and the role of miRNAs therein. Emerging treatment strategies combine therapies using innovative miRNA mimics or antagonizers with conventional approaches to maximize outcomes of patients with cancer.

Hay-Wells syndrome is caused by heterozygous missense mutations in the SAM domain of p63

Hay-Wells syndrome, also known as ankyloblepharon-ectodermal dysplasia-clefting (AEC) syndrome (OMIM 106260), is a rare autosomal dominant disorder characterized by congenital ectodermal dysplasia, including alopecia, scalp infections, dystrophic nails, hypodontia, ankyloblepharon and cleft lip and/or cleft palate. This constellation of clinical signs is unique, but some overlap can be recognized with other ectodermal dysplasia syndromes, for example ectrodactyly--ectodermal dysplasia--cleft lip/palate (EEC; OMIM 604292), limb--mammary syndrome (LMS; OMIM 603543), acro-dermato-ungual-lacrimal-tooth syndrome (ADULT; OMIM 103285) and recessive cleft lip/palate--ectodermal dysplasia (CLPED1; OMIM 225060). We have recently demonstrated that heterozygous mutations in the p63 gene are the major cause of EEC syndrome. Linkage studies suggest that the related LMS and ADULT syndromes are also caused by mutations in the p63 gene. Thus, it appears that p63 gene mutations have highly pleiotropic effects. We have analysed p63 in AEC syndrome patients and identified missense mutations in eight families. All mutations give rise to amino acid substitutions in the sterile alpha motif (SAM) domain, and are predicted to affect protein--protein interactions. In contrast, the vast majority of the mutations found in EEC syndrome are amino acid substitutions in the DNA-binding domain. Thus, a clear genotype--phenotype correlation can be recognized for EEC and AEC syndromes.