Stress granule-associated protein G3BP2 regulates breast tumor initiation.

Breast tumors contain tumorigenic cancer cells, termed "tumor-initiating cells" (TICs), which are capable of both replenishing themselves and giving rise to populations of nontumorigenic breast cancer cells (non-TICs). However, the molecular mechanisms responsible for breast tumor initiation remain poorly understood. Here we describe a chemical screening strategy to identify small molecules that enhance the effect of chemotherapeutic agents on TIC-enriched breast cancer cells. We identified proteins that interact with the lead compound C108, including the stress granule-associated protein, GTPase-activating protein (SH3 domain)-binding protein 2, G3BP2. G3BP2 regulates breast tumor initiation through the stabilization of Squamous cell carcinoma antigen recognized by T cells 3 (SART3) mRNA, which leads to increased expression of the pluripotency transcription factors Octamer-binding protein 4 (Oct-4) and Nanog Homeobox (Nanog). Our findings suggest that G3BP2 is important for the process of breast cancer initiation. Furthermore, these data suggest a possible connection between stress granule formation and tumor initiation in breast cancer cells.