Src homology domain-containing phosphatase 2 suppresses cellular senescence in glioblastoma.

BACKGROUND: Epidermal growth factor receptor (EGFR) signalling is frequently altered during glioblastoma de novo pathogenesis. An important downstream modulator of this signal cascade is SHP2 (Src homology domain-containing phosphatase 2). METHODS: We examined the The Cancer Genome Atlas (TCGA) database for SHP2 mutations. We also examined the expression of a further 191 phosphatases in the TCGA database and used principal component and comparative marker analysis available from the Broad Institute to recapitulate the TCGA-defined subgroups and identify the specific phosphatases defining each subgroup. We identified five siRNAs from two independent commercial sources that were reported by the vendor to be pre-optimised in their specificity of SHP2 silencing. The specificity and physiological effects of these siRNAs were tested using an in vitro glioma model. RESULTS: TCGA data demonstrate SHP2 to be mutated in 2% of the glioblastoma multiforme's studied. Both mutations identified in this study are likely to be activating mutations. We found that the four subgroups of GBM as defined by TCGA differ significantly with regard to the expression level of specific phosphatases as revealed by comparative marker analysis. Surprisingly, the four subgroups can be defined solely on the basis of phosphatase expression level by principal component analysis. This result suggests that critical phosphatases are responsible for the modulation of specific molecular pathways within each subgroup. Src homology domain-containing phosphatase 2 constitutes one of the 12 phosphatases that define the classical subgroup. We confirmed the biological significance by siRNA knockdown of SHP2. All five siRNAs tested reduced SHP2 expression by 70-100% and reduced glioblastoma cell line growth by up to 80%. Profiling the established molecular targets of SHP2 (ERK1/2 and STAT3) confirmed specificity of these siRNAs. The loss of cell viability induced by SHP2 silencing could not be explained by a significant increase in apoptosis alone as demonstrated by terminal deoxyribonucleotidyl transferase-mediated nick-end labelling and propidium iodide staining. Src homology domain-containing phosphatase 2 silencing, however, did induce an increase in ß-galactosidase staining. Propidium iodide staining also showed that SHP2 silencing increases the population of glioblastoma cells in the G1 phase of the cell cycle and reduces the population of such cells in the G2/M- and S-phase. CONCLUSION: Src homology domain-containing phosphatase 2 promotes the growth of glioblastoma cells by suppression of cellular senescence, a phenomenon not described previously. Selective inhibitors of SHP2 are commercially available and may be considered as a strategy for glioblastoma therapy.

FGFR3IIIS: a novel soluble FGFR3 spliced variant that modulates growth is frequently expressed in tumour cells.

Fibroblast growth factor receptor 3 (FGFR3) is one of four high-affinity tyrosine kinase receptors for the FGF family of ligands, frequently associated with growth arrest and induction of differentiation. The extracellular immunoglobulin (IgG)-like domains II and III are responsible for ligand binding; alternative usage of exons IIIb and IIIc of the Ig-like domain III determining the ligand-binding specificity of the receptor. By reverse transcriptase polymerase chain reaction (RT-PCR) a novel FGFR3IIIc variant FGFR3IIIS, expressed in a high proportion of tumours and tumour cell lines but rarely in normal tissues, has been identified. Unlike recently described nonsense transcripts of FGFR3, the coding region of FGFR3IIIS remains in-frame producing a novel protein. The protein product is coexpressed with FGFR3IIIc in the membrane and soluble cell fractions; expression in the soluble fraction is decreased after exposure to bFGF but not aFGF. Knockout of FGFR3IIIS using antisense has a growth-inhibitory effect in vitro, suggesting a dominant-negative function for FGFR3IIIS inhibiting FGFR3-induced growth arrest. In summary, alternative splicing of the FGFR3 Ig-domain III represents a mechanism for the generation of receptor diversity. FGFR3IIIS may regulate FGF and FGFR trafficking and function, possibly contributing to the development of a malignant phenotype.

Induction of cell death by basic fibroblast growth factor in Ewing's sarcoma.

Ewing's sarcoma is thought to arise after developmental arrest of primitive neural cells during embryogenesis. Because basic fibroblast growth factor (bFGF) has a critical role in the regulation of cell survival, proliferation, and differentiation during embryogenesis, we have tested the hypothesis that bFGF and FGF receptors may contribute to the development of Ewing's sarcoma and may provide a mechanism for the modulation of their behavior. All four of the Ewing's sarcoma cell lines examined expressed bFGF and FGF receptors, which were detected by immunofluorescence and Western blotting. bFGF-induced a significant dose-dependent decrease in Ewing's sarcoma cell proliferation on plastic and reduced anchorage-independent growth in soft agar. Unexpectedly, this decrease in cell number reflected bFGF-induced apoptosis and necrosis, as demonstrated by electron microscopy, binding of annexin V, and staining with acridine orange. Induction of cell death was dependent on dosage of, and period of exposure to, bFGF. bFGF did not induce differentiation of Ewing's sarcoma cells in either the presence or the absence of serum or nerve growth factor. Treatment of NuNu mice with bFGF decreased growth of the highly tumorigenic Ewing's sarcoma cell lines. Histologically tumors grown in the NuNu mice treated with bFGF were less cellular than those in control mice, and showed an increased level of apoptotic nuclei. This is in contrast to the mitogenic effect bFGF has in most other cancer cells. In summary, bFGF decreases Ewing's sarcoma growth in vitro and in vivo by the induction of cell death. This novel observation may provide a new therapeutic strategy for Ewing's sarcomas.