Efficient and reversible Cas13d-mediated knockdown with an all-in-one lentivirus-vector

TFE3-SLC36A1 axis promotes resistance to glucose starvation in kidney cancer cells

Higher demand for nutrients including glucose is characteristic of cancer. "Starving cancer" has been pursued to curb tumor progression. An intriguing regime is to inhibit glucose transporter GLUT1 in cancer cells. In addition, during cancer progression, cancer cells may suffer from insufficient glucose supply. Yet, cancer cells can somehow tolerate glucose starvation. Uncovering the underlying mechanisms shall shed insight into cancer progression and benefit cancer therapy. TFE3 is a transcription factor known to activate autophagic genes. Physiological TFE3 activity is regulated by phosphorylation-triggered translocation responsive to nutrient status. We recently reported TFE3 constitutively localizes to the cell nucleus and promotes cell proliferation in kidney cancer even under nutrient replete condition. It remains unclear whether and how TFE3 responds to glucose starvation. In this study, we show TFE3 promotes kidney cancer cell resistance to glucose starvation by exposing cells to physiologically relevant glucose concentration. We find glucose starvation triggers TFE3 protein stabilization through increasing its O-GlcNAcylation. Furthermore, through an unbiased functional genomic study, we identify SLC36A1, a lysosomal amino acid transporter, as a TFE3 target gene sensitive to TFE3 protein level. We find SLC36A1 is overexpressed in kidney cancer, which promotes mTOR activity and kidney cancer cell proliferation. Importantly, SLC36A1 level is induced by glucose starvation through TFE3, which enhances cellular resistance to glucose starvation. Suppressing TFE3 or SLC36A1 significantly increases cellular sensitivity to GLUT1 inhibitor in kidney cancer cells. Collectively, we uncover a functional TFE3-SLC36A1 axis that responds to glucose starvation and enhances starvation tolerance in kidney cancer.

The P53-P21-RB1 pathway promotes BRD4 degradation in liver cancer through USP1

Liver cancer is notoriously refractory to conventional therapeutics. Tumor progression is governed by the interplay between tumor-promoting genes and tumor-suppressor genes. BRD4, an acetyl lysine-binding protein, is overexpressed in many cancer types, which promotes activation of a pro-tumor gene network. But the underlying mechanism for BRD4 overexpression remains incompletely understood. In addition, understanding the regulatory mechanism of BRD4 protein level will shed insight into BRD4-targeting therapeutics. In this study, we investigated the potential relation between BRD4 protein level and P53, the most frequently dysregulated tumor suppressor. By analyzing the TCGA datasets, we first identify a strong negative correlation between protein levels of P53 and BRD4 in liver cancer. Further investigation shows that P53 promotes BRD4 protein degradation. Mechanistically, P53 indirectly represses the transcription of USP1, a deubiquitinase, through the P21-RB1 axis. USP1 itself is also overexpressed in liver cancer and we show USP1 deubiquitinates BRD4 in vivo and in vitro, which increases BRD4 stability. With cell proliferation assays and xenograft model, we show the pro-tumor role of USP1 is partially mediated by BRD4. With functional transcriptomic analysis, we find the USP1-BRD4 axis upholds expression of a group of cancer-related genes. In summary, we identify a functional P53-P21-RB1-USP1-BRD4 axis in liver cancer.