ABSTRACT
OBJECTIVE: Ewing sarcoma (ES) is a type of childhood cancer probably arising from stem mesenchymal or neural crest cells. The epidermal growth factor receptor (EGFR) acts as a driver oncogene in many types of solid tumors. However, its involvement in ES remains poorly understood. METHODS: Human SK-ES-1 and RD-ES ES cells were treated with EGF, the EGFR inhibitor tyrphostin (AG1478), or phosphoinositide 3-kinase (PI3K) or extracellular-regulated kinase (ERK)/mitogen-activated kinase (MAPK) inhibitors. Cell proliferation survival, cycle, and senescence were analyzed. The protein content of possible targets of EGFR manipulation was measured by Western blot. RESULTS: Cell proliferation and survival were increased by EGF and inhibited by AG1478. The EGFR inhibitor also altered the cell cycle, inducing arrest in G1 and increasing the sub-G1 population, reduced polyploidy and increased the population of senescent cells. In addition, AG1478 reduced the levels of phosphorylated AKT (p-AKT), ERK, p-ERK, cyclin D1, and brain-derived neurotrophic factor (BDNF), while enhancing p53 levels. Cell proliferation was also impaired by inhibitors of PI3K or ERK, alone or combined with AG1478. CONCLUSIONS: Our findings reveal novel aspects of EGFR regulation of ES cells and provide early evidence for antitumor activities of EGFR inhibitors in ES.
Subject(s)
Bone Neoplasms/pathology , Cell Proliferation/drug effects , Enzyme Inhibitors/pharmacology , ErbB Receptors/metabolism , Quinazolines/pharmacology , Sarcoma, Ewing/pathology , Tyrphostins/pharmacology , Brain-Derived Neurotrophic Factor/metabolism , Cell Line, Tumor , Cyclin D1/metabolism , Epidermal Growth Factor/pharmacology , ErbB Receptors/antagonists & inhibitors , Extracellular Signal-Regulated MAP Kinases/antagonists & inhibitors , G1 Phase Cell Cycle Checkpoints/drug effects , Humans , Phosphoinositide-3 Kinase Inhibitors , Phosphorylation/drug effects , Signal Transduction/drug effects , Tumor Suppressor Protein p53/metabolismABSTRACT
Germline mutations in TP53 are the underlying defects in Li-Fraumeni syndrome (LFS) and its variant, Li-Fraumeni-like (LFL) Syndrome, autosomal dominant disorders that are characterized by predisposition to multiple early onset cancers. Here, we identified rs78378222 (A > C), a rare variant that is located in the 3' untranslated region (3' UTR) of TP53, in 7 probands (5.4%) of a cohort from LFS/LFL patients without TP53 germline mutations in the coding regions. To support its association with the LFS/LFL phenotype, we assessed p53 expression in tumor specimens and fibroblasts from rs78378222[C] carriers. Additionally, we investigated using in silico tools the evolutionary conservation and whether rs78378222[C] affects microRNA (miRNA) binding sites in the 3' UTR of TP53 mRNA. We found lower p53 protein levels in biological samples from rs78378222[C] carriers. Additionally, we showed that rs78378222[C] could interfere with a putative target site of miR-545-3p, a novel miRNA that is predicted to directly target the 3' UTR TP53. To our knowledge, this is the first description of rs78378222[C] in LFS/LFL patients. Moreover, these findings suggest that rs78378222[C] lead to haploinsufficiency of p53, a new mechanism of carcinogenesis in LFS/LFL.
