MMP14 empowers tumor-initiating breast cancer cells under hypoxic nutrient-depleted conditions

Tumor-initiating cells (TICs) exist in breast cancer and are thought to be the cause of tumor initiation, progression, and relapse. In these processes, proteases play an important role. Additionally, conditions of the tumor milieu, including hypoxic nutrient-deprived as well as normoxic nutrient-rich environments, influence the tumor-promoting actions of neoplastic cells. Therefore, we investigated the role of proteases in TICs and their response to different environments by means of a generated immortalized TIC line. After assessing immortalized TIC tumorigenicity by limiting dilution assays in vivo and their characteristics in different environmental conditions, a transcriptome analysis was performed of iTICS cultured in hypoxic stem cell conditions and 1-7 days in normoxic standard condtitions. A high proteolytic signature was identified and further investigated by inhibitor treatment and shRNA mediated RNA interference of Mmp14. Immortalized tumor-initiating cells (iTICs) were grown in hypoxic stem cell conditions (HSCC) or normoxic standard conditions till confluency of 80% on a 10 cm petridish. Subsequently, total RNA was extracted, analyzed for their quality (RIN), and hybridized to a Mouse WG-6 v2.0 Bead Chip (Illumina). To obtain an overview of expression profile over time iTICs are cultured in NSC, in addition to the HSCC replicates (3x), samples of iTICs cultured in NSC for 1, 2, 3, 4, 5, 6, and 7 days NSC were analyzed. The 7 day sample in NSC was also analyzed in triplicate while all other days in NSC were analyze as one replicate.