Hahm, E.-R. | Search bioRxiv

bioRxiv2020

Novel mechanistic targets of Forkhead box Q1 transcription factor in human breast cancer cells

The transcription factor forkhead box Q1 (FoxQ1), which is overexpressed in different solid tumors, has emerged as a key player in the pathogenesis of breast cancer by regulating epithelial-mesenchymal transition, maintenance of cancer-stem like cells, and metastasis. However, the mechanism underlying oncogenic function of FoxQ1 is still not fully understood. In this study, we compared the RNA-seq data from FoxQ1 overexpressing SUM159 cells with that of empty vector-transfected control (EV) cells to identify novel mechanistic targets of this transcription factor. Consistent with published results in basal-like subtype, immunohistochemistry revealed upregulation of FoxQ1 protein in luminal-type human breast cancer tissue microarrays when compared to normal mammary tissues. Many previously reported transcriptional targets of FoxQ1 (e.g., E-cadherin, N-cadherin, fibronectin 1, etc.) were verified from the RNA-Seq analysis. FoxQ1 overexpression resulted in downregulation of genes associated with cell cycle checkpoints, M phase, and cellular response to stress/external stimuli as evidenced from the Reactome pathway analysis. Consequently, FoxQ1 overexpression resulted in S, G2M and mitotic arrest in basal-like SUM159 and HMLE cells, but not in luminal-type MCF-7 cells. There were differences in expression of cell cycle-associated proteins between FoxQ1 overexpressing SUM159 and MCF-7 cells. Finally, we show for the first time that FoxQ1 is a direct transcriptional regulator of interleukin (IL)-1, IL-8, and vascular endothelial growth factor in breast cancer cells. Chromatin immunoprecipitation revealed FoxQ1 occupancy at the promoters of IL-1, IL-8, and VEGF. In conclusion, the present study reports novel mechanistic targets of FoxQ1 in human breast cancer cells.

cancer biology↗

bioRxiv2019

Super-resolution imaging reveals the evolution of higher-order chromatin folding in early carcinogenesis

Aberrant chromatin structure is a hallmark in cancer cells and has long been used for clinical diagnosis of cancer. However, underlying higher-order chromatin folding during malignant transformation remains elusive, due to the lack of molecular scale resolution. Using optimized stochastic optical reconstruction microscopy (STORM) for pathological tissue (PathSTORM), we uncovered a gradual decompaction and fragmented higher-order chromatin folding throughout all stages of carcinogenesis in multiple tumor types, even prior to the tumor formation. Our integrated imaging, genomic, and transcriptomic analyses reveal the functional consequences in enhanced formation of transcription factories, spatial juxtaposition with relaxed nanosized chromatin domains and impaired genomic stability. We also demonstrate the potential of imaging higher-order chromatin decompaction to detect high-risk precursors that cannot be distinguished by conventional pathology. Taken together, our findings reveal the gradual decompaction and fragmentation of higher-order chromatin structure as an enabling characteristic in early carcinogenesis to facilitate malignant transformation, which may improve cancer diagnosis, risk stratification, and prevention.\n\nSIGNIFICANCEGenomic DNA is folded into a higher-order structure that regulates transcription and maintains genomic stability. Although much progress has been made on understanding biochemical characteristics of epigenetic modifications in cancer, the higher-order folding of chromatin structure remains largely unknown. Using optimized super-resolution microscopy, we uncover de-compacted and fragmented chromatin folding in tumor initiation and stepwise progression in multiple tumor types, even prior to the presence of tumor cells. This study underlines the significance of unfolding higher-order chromatin structure as an enabling characteristic to promote tumorigenesis, which may facilitate the development and evaluation of new preventive strategies. The potential of imaging higher-order chromatin folding to improve cancer detection and risk stratification is demonstrated by detecting high-risk precursors that cannot be distinguished by conventional pathology.

cancer biology↗