FUS/TLS Is a Novel Mediator of Androgen-Dependent Cell-Cycle Progression and Prostate Cancer Growth

Abstract

Progression of prostate cancer is highly dependent upon the androgen receptor pathway, such that knowledge of androgen-regulated proteins is vital to understand and combat this disease. Using a proteomic screen, we found the RNA-binding protein FUS/TLS (Fused in Ewing's Sarcoma/Translocated in Liposarcoma) to be downregulated in response to androgen. FUS has recently been shown to be recruited by noncoding RNAs to the regulatory regions of target genes such as cyclin D1, in which it represses transcription by disrupting complex formation. Here we show that FUS has some characteristics of a putative tumor suppressor, as its overexpression promoted growth inhibition and apoptosis of prostate cancer cells, whereas its knockdown increased cell proliferation. This effect was reproducible in vivo, such that increasing FUS levels in tumor xenografts led to dramatic tumor regression. Furthermore, FUS promoted conditions that favored cell-cycle arrest by reducing the levels of proliferative factors such as cyclin D1 and Cdk6 and by increasing levels of the antiproliferative Cdk inhibitor p27. Immunohistochemical analysis revealed that FUS expression is inversely correlated with Gleason grade, demonstrating that patients with high levels of FUS survived longer and were less likely to have bone metastases, suggesting that loss of FUS expression may contribute to cancer progression. Taken together, our results address the question of how androgens regulate cell-cycle progression, by demonstrating that FUS is a key link between androgen receptor signaling and cell-cycle progression in prostate cancer.

Identification, by systematic RNA sequencing, of novel candidate biomarkers and therapeutic targets in human soft tissue tumors

“…53 The protein FUsed/Translocated in LipoSarcoma (FUS/TLS) binds to the androgen receptor and mediates androgen-dependent cell-cycle progression and prostate cancer growth. 54,55 A loss of FUS/ TLS results in decreased cellular proliferation, impaired RNA processing, and increased expression of the closely related Ewing's sarcoma protein EWS. 56 Indeed, the transactivation domains of the TET family of RNA-binding proteins (such as FUS and EWS) may be interchangeable and FUS/ERG fusions have been reported in Ewing's sarcoma patients.…”

RNA-binding proteins as molecular links between cancer and neurodegeneration

“…The overexpression of FUS/TLS promotes growth inhibition and apoptosis of prostate cancer cells, whereas its knockdown increases cell proliferation. FUS/TLS induces conditions that favor cell-cycle arrest by reducing the levels of proliferative factors such as cyclin D1 and Cdk6 and by increasing levels of the anti-proliferative Cdk inhibitor p27 (Brooke et al 2011).…”

“…On the one hand, it has been reported that the overexpression of FUS/ TLS significantly retards androgen-induced prostate cancer cell growth in vitro and in vivo (Brooke et al 2011). In contrast, it has also been observed that the reduction of FUS/TLS levels limited androgeninduced proliferation of the tumors (Haile et al 2011).…”

Engineered repressors are potent inhibitors of androgen receptor activity

“…One possible mechanism to explain therapy failure leading to CRPC is alterations in levels and/or activities of AR co-regulators sensitising the pathway to low levels or weakly androgenic ligands. Indeed, Gregory et al ., demonstrated that the coactivators SRC1 (Steroid Receptor Coactivator 1) and TIF2 (transcriptional intermediary factor 2) were over-expressed in the majority of CRPCs [29], and altered expression and localisation of AR corepressors in prostate cancer has also been described (for example [30-34]). To determine whether the engineered repressors can inhibit AR activity enhanced by coactivator over-expression, COS1 cells were transfected with expression plasmids for the AR, SRC1 and increasing amounts of engineered repressor.…”

“…Lysates were pre-cleared with 50 μl of sepharose beads (Sigma-Aldrich, MO, USA, 30min of rotation at 4°C), supernatant transferred to fresh tubes and incubated with anti-GFP antibody (Abcam, Cambridge, UK) for 1hr with rotation before addition of 50 μl of sepharose beads. After 1hr, beads were washed 3 times with IP buffer, laemmli loading buffer added to the beads and samples boiled before protein separation using immunoblotting, as previously described [30]. …”