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Magdalena Losko, PhD

Pronouns

She/Her/Hers

Job Title

Research Fellow

Academic Rank

Research Fellow

Department

Medicine

Authors

Magdalena Losko, Clemens K Probst, Elio Adib, Heng Du, Michelle Hirsch, Krinio Giannikou, David J Kwiatkowski

Principal Investigator

David Kwiatkowski

Research Category: Cancer

Tags

TSC1 mutant bladder cancer is characterized by a lysosomal gene signature due to nuclear localization of TFE3 - a potential targetable dependency?

Scientific Abstract

Inactivating mutations in the TSC1 occur in approximately 6-10% of all bladder cancer. The TSC1 subunit is a part of the TSC complex, a negative regulator of the small GTPase Rheb and mTORC1 in cellular stress signaling.
Here, we characterize TSC1-mutated bladder cancers (TSC1mutBLCA, n=26) with TSC1 wildtype tumors (TSC1WTBLCA, n=382) using the TCGA expression data set. We showed that TSC1mutBLCA were enriched in lysosomal gene expression, with GPNMB and SQSTM1 genes showing the greatest increase in TCGA. We confirmed the expression differences by IHC analysis of five independent TSC1mutBLCA and TSC1WTBLCA specimens each, and by in vitro studies using three TSC1mut and five TSC1WT BLCA cell lines. Notably, we identified that TFE3, a regulator of lysosomal gene expression, was elevated in expression and localized to the nucleus in TSC1mutBLCA by IHC on BWH BLCA cases. Mechanistic analysis of TSC1mutBLCA cell lines showed that nuclear localization of TFE3 was partially reversed by rapamycin (mTOR inhibitor) treatment, leading to reduced expression of lysosomal genes. Furthermore, siRNA-mediated TFE3 knock-down showed decreased viability of TSC1mutBLCA cells compared to TSC1WTBLCA cells. Our study indicates that TSC1mutBLCA are characterized by activation of TFE3, which likely contributes to cancer development and is a potential therapeutic target.

Lay Abstract

Inactivating mutations in the TSC1 occur in approximately 6-10% of all bladder cancer. TSC1 is a tumor suppressor, preventing cells from growing and dividing in an uncontrolled way. Here, we provide a detailed characterization of TSC1-mutated bladder cancers (TSC1mutBLCA, n=26), comparing them to TSC1 wildtype tumors (TSC1WTBLCA, n=382) using The Cancer Genome Atlas gene expression data set. Our expression analysis was validated by immunohistochemistry (IHC) staining of five independent TSC1mutBLCA and TSC1WTBLCA specimens each. We showed that TSC1mutBLCA have an elevated level of genes coding proteins necessary for lysosomes, cellular compartments acting as recycling centers within cells. Notably, we found that this phenotype is caused by the nuclear localization of TFE3, a regulator of lysosomal gene expression. Our observations were confirmed by in vitro studies using three TSC1mutBLCA and five TSC1WTBLCA cell lines. We showed that nuclear localization of TFE3 was partially reversed by rapamycin (mTOR inhibitor) treatment, leading to a reduced level of lysosomal proteins in TSC1mutBLCA cells. Furthermore, silencing of the TFE3 gene showed decreased viability of TSC1mutBLCA cells compared to TSC1WTBLCA cells. Our study indicates that TSC1-mutated bladder cancers are characterized by activation of TFE3, which likely contributes to cancer development and is a potential therapeutic target.

Clinical Implications

Treatment of TSC1-mutated bladder cancer with rapalogs has had limited success. Our findings revealed that functional loss of TSC1 and activation of TFE3 are likely driver events contributing to TSC1-mutated bladder cancer development and may be amenable to targeted therapy.