Mutations in EGFR compromise hypoxia associated radiation resistance through impaired repair of replication fork associated DNA double-strand breaks
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE95564 | GEO | 2017/03/02
SECONDARY ACCESSION(S): PRJNA377535
REPOSITORIES: GEO
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Project description:Haploinsufficiency of factors governing genome stability underlies hereditary breast and ovarian cancer. One significant pathway that is disabled as a result is homologous recombination repair (HRR). With the aim of identifying new candidate genes, we examined early-onset breast cancer patients negative for BRCA1 and BRCA2 pathogenic variants. Here, we focused on CtIP (RBBP8 gene), which mediates HRR through the end resection of DNA double-strand breaks (DSBs). Notably, these patients exhibited a number of rare germline RBBP8 variants. Functional analysis revealed that these variants did not affect DNA DSB end resection efficiency. However, expression of a subset of variants led to deleterious nucleolytic degradation of stalled DNA replication forks in a manner similar to that of cells lacking BRCA1 or BRCA2. In contrast to BRCA1 and BRCA2, CtIP deficiency promoted the helicase-driven destabilization of RAD51 nucleofilaments at damaged DNA replication forks. Taken together, our work identifies CtIP as a critical regulator of DNA replication fork integrity, which, when compromised, may predispose to the development of early-onset breast cancer.
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Project description:We previously reported that differential protein degradation of TKI-sensitive [L858R, del(E746-A750)] and resistant (T790M) epidermal growth factor receptor (EGFR) mutants upon erlotinib treatment correlates with drug sensitivity. However, the molecular mechanism remains unclear. We also reported SMAD ubiquitination regulatory factor 2 (SMURF2) as a stabilizer of EGFR in a ligase (E3) activity-dependent manner. Here, using in vitro and in vivo ubiquitination assays, mass spectrometry, and super-resolution microscopy, we show SMURF2-EGFR functional interaction is critical in receptor stability and TKI sensitivity. We found that L858R/T790M EGFR is a preferred substrate of SMURF2-UBCH5 (an E3-E2) complex-mediated K63-linked polyubiquitination, which preferentially stabilizes mutant receptor. We identified three lysine (K) residues (K721, 1037 and 1164) as the sites of ubiquitination and replacement of K to acetylation-mimicking asparagine (Q) at K1037 position in L858R/T790M background converts the stable protein sensitive to erlotinib-induced degradation. Using STochastic Optical Reconstruction Microscopy (STORM) imaging, we show that SMURF2 presence allows longer membrane retention of activated EGFR upon EGF treatment, whereas, siRNA-mediated SMURF2 knockdown fastens receptor endocytosis and lysosome enrichment. In an erlotinib-sensitive PC9 cells, SMURF2 overexpression increased EGFR levels with improved erlotinib tolerance, whereas, SMURF2 knockdown decreased EGFR steady state levels in NCI-H1975 and PC9-AR cells to overcome erlotinib and AZD-9291 resistance respectively. Additionally, disruption of the SMURF2-UBCH5 complex destabilized EGFR. Together, we propose that SMURF2-mediated preferential polyubiquitination of L858R/T790M EGFR may be competing with acetylation-mediated receptor internalization to provide enhanced receptor stability and that disruption of the E3-E2 complex may be an attractive alternate to overcome TKI resistance
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Project description:Mutations in the epidermal growth factor receptor (EGFR) kinase domain occur in 10-30% of lung adenocarcinoma. Leucine to arginine substitution at amino acid position 858 (L858R) accounts for around 50% of EGFR-tyrosine kinase inhibitor (TKI) sensitizing mutations. A second site mutation in the gatekeeper residue (T790M) accounts for around 60% of acquired resistance to EGFR-TKIs. We sought to identify the immediate direct and indirect targets of these mutant EGFRs in lung adenocarcinoma and their modulation by erlotinib, the first generation, and most widely used EGFR-directed TKI. We undertook stable isotope labeling of amino acids in cell culture (SILAC), phosphopeptide enrichment, and quantitative mass spectrometry to identify dynamic changes of phosphorylation downstream of mutant EGFRs in lung adenocarcinoma cells harboring L858R or L858R/T790M mutations and their modulation by erlotinib inhibition. Phosphorylation at the majority of phosphosites identified exhibited no change upon either EGF stimulation or erlotinib inhibition. Only around 7% of phosphosites identified and quantified showed increased phosphorylation upon EGF stimulation in either cell line. However, while phosphorylation at 61% of these phosphosites decreased upon erlotinib inhibition in the TKI sensitive H3255 cells, only 24% of such sites exhibited decreased phosphorylation upon erlotinib inhibition in the TKI resistant H1975 cells. Top canonical pathways that were inhibited upon erlotinib treatment in sensitive cells, but not the resistant cells include EGFR, Insulin receptor, HGF, MAPK, mTOR, p70S6K and JAK/STAT signaling. We identified phosphosites in proteins of the autophagy network, such as ULK1 (S623) that is constitutive phosphorylated in these lung adenocarcinoma cells, but phosphorylation is inhibited upon erlotinib treatment in sensitive cells, but not resistant cells. Finally, kinase-substrate prediction analysis from our data indicated that substrates of basophilic kinase families, AGC, CAMK and STE were significantly enriched and those of proline directed kinase families, CMGC and CK were significantly depleted among substrates that exhibit increased phosphorylation upon EGF stimulation and reduced phosphorylation upon TKI inhibition. This is the first study to date to examine global phosphorylation changes upon erlotinib treatment of lung adenocarcinoma cells and results from this study provide new insights into signaling downstream of mutant EGFRs in lung adenocarcinoma.
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Project description:Controlled activation of epidermal growth factor receptor (EGFR) is systematically guaranteed at the molecular level, however aberrant activation of EGFR is frequently found in cancer. Transcription induced by EGFR activation often involves coordinated expression of genes that positively and negatively regulate the original signaling pathway, therefore alterations in EGFR kinase activity may reflect changes in gene expression associated with the pathway. In this study, we investigated transcriptional changes following EGF stimulation with or without the EGFR kinase inhibitor Iressa in H1299 human non-small-cell lung cancer cells (parental H1299, H1299 cells which overexpress wild-type: EGFR-WT and mutant EGFR: L858R). Our results clearly showed differences in transcriptional activity in the absence or presence of EGFR kinase activity, and genes sharing the same molecular functions showed distinct expression dynamics. The results showed particular enrichment of EGFR/ErbB signaling-related genes in a differentially expressed gene set, and significant protein expression of MIG6/RALT(ERRFI1), an EGFR negative regulator, was confirmed in L858R. High MIG6 protein expression was correlated with basal EGFR phosphorylation and inversely correlated with EGF-induced ERK phosphorylation levels. Investigation of NCI-60 cell lines showed that ERRFI1 expression was correlated with EGFR expression regardless of tissue type. These results suggest that cells accumulate MIG6 as an inherent negative regulator to suppress excess EGFR activity when basal EGFR kinase activity is considerably high. Taken together, an EGFR mutation can cause transcriptional changes to accommodate the activation potency of the original signaling pathway at the cellular level. Experiment Overall Design: H1299 human non-small cell lung cancer cells were stimulated by the growth hormone (epidermal growth factor (EGF)) or EGFR kinase inhibitor (Iressa). Control was set as non-treated cells.
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