Pang, Mei-Fong

Abstract Breast tumors are stiff and hypoxic. Nevertheless, it remains unclear how stiff and hypoxic conditions within the tumor microenvironment promote breast cancer progression. Using an innovative engineered culture model to recapitulate these features, we found that, under stiff and hypoxic conditions, breast cancer cells have enhanced integrin-linked kinase (ILK) expression and acquire cancer stem cell (CSC)-like traits, suggesting tissue stiffness and oxygen tension can modulate ILK expression to induce breast CSC formation. Knocking down ILK impairs the mechanosensing of invasive breast cancer cells on stiff microenvironments, inhibits CSC markers and properties. In contrast, ectopic expression of ILK promotes breast CSC formation. In addition to promoting CSC-like phenotype, microarray analysis reveals that stiff and hypoxic microenvironments also regulate genes involved in mRNA processing, splicing and the spliceosome. These data suggest that the non-cellular compartment of the tumor microenvironment, namely tissue mechanics and oxygen tension, can promote breast cancer progression by controlling mechanotransduction and post-transcriptional regulation of breast cancer cells. Note: This abstract was not presented at the meeting. Citation Format: Mei-Fong Pang, Derek C. Radisky, Celeste M. Nelson. Role of tissue stiffness and oxygen tension in promoting breast cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5943. doi:10.1158/1538-7445.AM2017-5943

Abstract The mechanical and chemical properties of the cellular microenvironment can influence the phenotype of cancer cells. The hypoxic conditions within solid breast tumors can contribute to invasiveness and the formation of breast cancer stem cells (CSCs). Integrin-linked kinase (ILK) is a critical mediator for mechanotransduction, a process that converts exogenous mechanical stimuli into biochemical signals. Yet, it is unclear how the physical properties of the tumor microenvironment, including matrix stiffness and hypoxia, integrate to direct the formation of the breast CSC niche. Using an innovative engineered culture model, we found that stiff and hypoxic microenvironments activate integrin signaling and a stem-like gene signature in breast cancer cells, suggesting that integrin signaling, matrix mechanics and oxygen tension cooperatively promote the formation of breast CSCs. Stiff and hypoxic microenvironments promote integrin signaling and the expression of CSC markers including CD44 and Nanog. Knocking down ILK reverts the CSC phenotype of invasive breast cancer cells on stiff matrix, and abrogates their ability to form mammospheres and colonies in soft agar. In contrast, ectopic expression of ILK enhances CSC properties. ILK promotes integrin signaling and the CSC phenotype through the PI3K/Akt pathway. Stiff microenvironments promote tumor formation and metastasis in ovo. ILK depletion significantly abrogates the tumorigenenic and metastatic potential of invasive breast cancer cells in ovo. Importantly, we found that breast cancer cells expressing ILK and the CSC marker CD44 were only present in the regions of tumors predicted to be stiff in breast cancer patient samples. Our data suggest that ILK act as an essential mechanosensor that regulates breast CSC phenotype in response to matrix mechanics and oxygen tension to regulate the formation of breast CSCs. Citation Format: Mei-Fong Pang, Melody Stallings-Mann, Michael J. Siedlik, Victor D. Varner, Siyang Han, Derek C. Radisky, Celeste M. Nelson. Tissue stiffness and hypoxia regulate breast cancer stem cells through ILK. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4395.