Epidermal Growth Factor Receptor Regulation of Ewing Sarcoma Cell Function.

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.

Rare germline variant (rs78378222) in the TP53 3' UTR: Evidence for a new mechanism of cancer predisposition in Li-Fraumeni syndrome.

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.