A Lysosome independent role for TFEB in activating DNA repair and inhibiting apoptosis in breast cancer cells

Transcription factor EB (TFEB) is a master regulator of lysosomal biogenesis and autophagy with critical roles in several cancers. Lysosomal autophagy promotes cancer survival through degradation of toxic molecules and maintenance of adequate nutrient supply. Doxorubicin (DOX) is the standard of care treatment for triple-negative breast cancer (TNBC); however, chemoresistance at lower doses and toxicity at higher doses limit its usefulness. By targeting pathways of survival, DOX can become an effective antitumor agent. In this study, we examined the role of TFEB in TNBC and its relationship with autophagy and DNA damage induced by DOX. In TNBC cells, TFEB was hypo-phosphorylated and localized to the nucleus upon DOX treatment. TFEB knockdown decreased the viability of TNBC cells while increasing caspase-3 dependent apoptosis. Additionally, inhibition of TFEB-phosphatase calcineurin sensitized cells to DOX-induced apoptosis in a TFEB dependent fashion. Regulation of apoptosis by TFEB was not a consequence of altered lysosomal function, as TFEB continued to protect against apoptosis in the presence of lysosomal inhibitors. RNA-Seq analysis of TFEB knockdown MDA-MB-231 cells identified a significant downregulation in cell cycle and homologous recombination while genes involved in interferon-γ and TNFα signaling were upregulated. In consequence, knockdown of TFEB was found to disrupt DNA repair following DOX, as evidenced by persistent γH2A.X detection. Together, these findings describe in TNBC a novel lysosomal independent function for TFEB in responding to DNA damage. MDA-MB-231 cells were transfected with either of two siRNA’s targeting TFEB (n=3 for each siRNA) or a non-targeting control (n=4) and cultured for 48 h before cells were harvested and RNA extracted using the Qiagen RNeasy mini kit according to the manufacturer’s instructions.