FGFR4 signaling couples to Bim and not Bmf to discriminate subsets of alveolar rhabdomyosarcoma cells

Abstract

Biological heterogeneity represents a major obstacle for cancer treatment. Therefore, characterization of treatment-relevant tumor heterogeneity is necessary to develop more effective therapies in the future. Here, we uncovered population heterogeneity among PAX/FOXO1-positive alveolar rhabdomyosarcoma by characterizing prosurvival networks initiated by FGFR4 signaling. We found that FGFR4 signaling rescues only subgroups of alveolar rhabdomyosarcoma cells from apoptosis induced by compounds targeting the IGF1R-PI3K-mTOR pathway. Differences in both proapoptotic machinery and FGFR4-activated signaling are involved in the different behavior of the phenotypes. Proapoptotic stress induced by the kinase inhibitors is sensed by Bim/Bad in rescue cells and by Bmf in nonrescue cells. Anti-apoptotic ERK1/2 signaling downstream of FGFR4 is long-lasting in rescue and short-termed in most non-rescue cells. Gene expression analysis detected signatures specific for these two groups also in biopsy samples. The different cell phenotypes are present in different ratios in alveolar rhabdomyosarcoma tumors and can be identified by AP2b expression levels. Hence, inhibiting FGFR signaling might represent an important strategy to enhance efficacy of current RMS treatments.

The proprotein convertase furin is required to maintain viability of alveolar rhabdomyosarcoma cells

“…This indicates that furin silencing primarily triggers the intrinsic apoptotic pathway. Others have shown that disruption of the IGF1R and/or PI3K/mTOR pathways leads to apoptosis in Rh3 and Rh4 cell lines [12, 33]. In this study we found evidence that activation of the IGF signaling pathway is dependent on furin activity.…”

“…Therefore, we examined the cell cycle distribution of Rh4 and Rh3 cells 72h after DOX treatment and found a clear increase of cells in sub-G1 phase (Figure 3A - shFAi: 54-62%, shFEi: 26-32%). As a positive control for apoptosis we treated aRMS cells with a combination of 1 μM of the IGF1R-inhibitor AEW451 (AEW) and 275 nM of the dual PI3K/mTOR inhibitor BEZ235 (BEZ) for 24h, conditions that induce apoptosis in aRMS cell lines [33]. As expected, treatment with BEZ/AEW led to an increase of cells in sub-G1 phase (Figure 3A - Rh4: 22%, Rh3: 18%).…”

Helicase CHD4 is an epigenetic coregulator of PAX3-FOXO1 in alveolar rhabdomyosarcoma

“…Preselection was based on number of unique peptides identified by MS combined with possible function as described in the literature. Additionally, we used gene expression data from different FP-RMSs to include only candidates with detectable expression levels (24). RH4 cells, whose gene expression signature represents most closely tumor biopsies (19,33), were individually transfected with 3 unique siRNA sequences per target and transcript levels of 5 PAX3-FOXO1 target genes measured after 48 hours.…”

“…Many putative therapeutically relevant signaling pathways have been described with varying degrees of tumor cells' dependence on them and therefore also varying tumor response upon inhibition. Also, their complexity, crosstalk, and acquired drug resistance often limit clinical application of drugs targeting key components of these pathways (23)(24)(25). Furthermore, pediatric cancers in general are known to carry very few mutations compared with adult tumors, and recent comprehensive genomic analysis has identified a particularly low overall mutational burden in FP-RMS, decreasing the number of potential actionable targets and underscoring the importance of the fusion proteins as dominant driver (26,27).…”

Prognostic roles for fibroblast growth factor receptor family members in malignant peripheral nerve sheath tumor

“…FGFR4 protein is expressed in the two main variants of RMS—embryonal RMS and alveolar RMS (aRMS). Interestingly, only certain subgroups of aRMS cells are rescued by FGFR4 signaling following induction of apoptosis by compounds targeting the IGF1R-PI3K-mTOR pathway [30–32]. Therefore, expression patterns of FGFRs could facilitate selection of patients for adjuvant systemic therapy.…”