The chromosomal translocation t(X;17)(p11;q25) is found in almost all cases of alveolar soft part sarcoma (ASPS) and a subset of renal cell carcinomas (RCCs), leading to the formation of the ASPSCR1::TFE3 fusion gene (Argani et al., 2001, Ladanyi et al., 2001). ASPS, a rare sarcoma of unknown origin, typically presents as a slow-growing tumor (Paoluzzi and Maki, 2019). However, its prognosis is generally poor because of the high incidence of metastasis and resistance to conventional chemotherapies (Folpe and Deyrup, 2006, Wilky et al., 2019). ASPSCR1::TFE3-positive RCC is a subset of Xp11.2 translocation RCC (Xp11.2 tRCC), a rare subtype of RCC. Xp11.2 tRCCs generally exhibit a more aggressive clinical course and a poorer prognosis compared to non-Xp11.2 tRCCs (Sukov et al., 2012). Among Xp11.2 tRCC, transcription factor enhancer 3 (TFE3) fuses with some different partners (Argani et al., 2016, Tang and Baba, 2023, Wei et al., 2022). Despite their different cellular origins, ASPS and ASPSCR1::TFE3-positive RCC share similar morphological and clinicopathological features, such as a young onset age and high metastasis rate, indicating the important role of ASPSCR1::TFE3 in the pathogenesis of these tumors.
TFE3 is a basic helix-loop-helix domain-containing transcription factor that binds to the E-box sequences (CANNTG) (Beckmann et al., 1990, Hemesath et al., 1994). The ASPSCR1::TFE3 fusion gene, resulting from the replacement of TFE3’s N-terminal region with ASPSCR1 sequences, retains the DNA-binding and activation domain of TFE3, giving rise to an aberrant transcriptional activator (Kobos et al., 2013, Ladanyi et al., 2001). This oncoprotein plays a crucial role in the tumorigenesis of ASPSCR1::TFE3-associated tumors by inducing inappropriate target gene transactivation (Fang et al., 2021, Kobos et al., 2013). ASPSCR1::TFE3 transcriptionally enhances the expression of MET, p21, and GPNMB, all of which are crucial for tumor progression (Tsuda et al., 2007, Ishiguro and Yoshida, 2016, Tanaka et al., 2017). However, the role of ASPSCR1::TFE3 in the oncogenic process remains largely unknown.
Insulin receptor substrates (IRSs) are cytoplasmic adaptor proteins that link signaling from cell surface receptors to multiple downstream effectors in receptor tyrosine kinase signaling pathways, including the insulin-like growth factor-1 receptor (IGF-1R) and insulin receptor pathways (Dearth et al., 2007, Mardilovich et al., 2009, Martínez Báez et al., 2024). Notably, IRS-2, despite lacking intrinsic kinase activity, contributes to tumor initiation and progression. Elevated expression of IRS-2 has been observed in many types of tumors, including mammary tumors, non-small cell lung cancers, colorectal cancers, and renal cell carcinomas (Day et al., 2013, Ma et al., 2015, Porter et al., 2013, Xu et al., 2018). As a common intermediate of various receptors implicated in tumor progression, IRS-2 plays a key role in regulating tumor cell responses to various extracellular stimuli (Mardilovich et al., 2009). Additionally, IRS-2 is often associated with the motility and metastatic potential of tumor cells (Dearth et al., 2006, Jackson et al., 2001, Liu et al., 2021).
A previous study demonstrated that TFE3 binds to the E-box sequence of the IRS-2 promoter and transactivates its expression (Nakagawa et al., 2006). Given that ASPSCR1::TFE3 retains the DNA-binding and activation domain of TFE3, we hypothesized that IRS-2 may be a candidate ASPSCR1::TFE3-regulated gene involved in tumor progression. Here, our findings confirm that IRS-2 is positively regulated by ASPSCR1::TFE3 and is highly expressed in ASPSCR1::TFE3-positive cells. Furthermore, we showed that IRS-2 depletion in ASPSCR1::TFE3-positive cells attenuates downstream PI3K/AKT signaling and reduces cell proliferation, migration, invasion, adhesion, and clonogenicity in vitro.