ABSTRACT
Aberrant alternative splicing (AS) is a hallmark of cancer and a potential target for novel anti-cancer therapeutics. Breast cancer-associated AS events are known to be linked to disease progression, metastasis, and survival of breast cancer patients. To identify altered AS programs occurring in metastatic breast cancer, we perform a global analysis of AS events by using RNA-mediated oligonucleotide annealing, selection, and ligation coupled with next-generation sequencing (RASL-seq). We demonstrate that, relative to low-metastatic, high-metastatic breast cancer cells show different AS choices in genes related to cancer progression. Supporting a global reshape of cancer-related splicing profiles in metastatic breast cancer we found an enrichment of RNA-binding motifs recognized by several splicing regulators, which have aberrant expression levels or activity during breast cancer progression, including SRSF1. Among SRSF1-regulated targets we found DCUN1D5, a gene for which skipping of exon 4 in its pre-mRNA introduces a premature termination codon (PTC), thus generating an unstable transcript degraded by nonsense-mediated mRNA decay (NMD). Significantly, distinct breast cancer subtypes show different DCUN1D5 isoform ratios with metastatic breast cancer expressing the highest level of the NMD-insensitive DCUN1D5 mRNA, thus showing high DCUN1D5 expression levels, which are ultimately associated with poor overall and relapse-free survival in breast cancer patients. Collectively, our results reveal global AS features of metastatic breast tumors, which open new possibilities for the treatment of these aggressive tumor types.
Subject(s)
Alternative Splicing/genetics , Breast Neoplasms/genetics , Breast Neoplasms/secondary , Base Sequence , Cell Line, Tumor , Exons/genetics , Female , Gene Expression Regulation, Neoplastic , Humans , Nonsense Mediated mRNA Decay/genetics , Oncogene Proteins/genetics , Oncogene Proteins/metabolism , Peptide Synthases/genetics , Peptide Synthases/metabolism , RNA Precursors/genetics , RNA Precursors/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Reproducibility of Results , Serine-Arginine Splicing Factors/genetics , Serine-Arginine Splicing Factors/metabolism , Survival AnalysisABSTRACT
BACKGROUND: Therapeutic management of Chronic Migraine (CM), often associated with Medication Overuse Headache (MOH), is chiefly empirical, as no biomarker predicting or correlating with clinical efficacy is available to address therapeutic choices. The present study searched for neurophysiological correlates of Greater Occipital Nerve Block (GON-B) effects in CM. METHODS: We recruited 17 CM women, of whom 12 with MOH, and 19 healthy volunteers (HV). Patients had no preventive treatment since at least 3 months. After a 30-day baseline, they received a bilateral betamethasone-lidocaine GON-B of which the therapeutic effect was assessed 1 month later. Habituation of visual evoked potentials (VEP) and intensity dependence of auditory evoked potentials (IDAP) were recorded before and 1 week after the GON-B. RESULTS: At baseline, CM patients had a VEP habituation not different from HV, but a steeper IDAP value than HV (p = 0.01), suggestive of a lower serotonergic tone. GON-B significantly reduced the number of total headache days per month (- 34.9%; p = 0.003). Eight out 17CM patients reversed to episodic migraine and medication overuse resolved in 11 out of 12 patients. One week after the GON-B VEP habituation became lacking respect to baseline (p = 0.01) and to that of HV (p = 0.02) like in episodic migraine, while the IDAP slope significantly flattened (p < 0.0001). GON-B-induced reduction in headache days positively correlated with IDAP slope decrease (rho = 0.51, p = 0.03). CONCLUSIONS: GON-B may be effective in the treatment of CM, with or without MOH. The pre-treatment IDAP increase is compatible with a weak central serotonergic tone, which is strengthened after GON-B, suggesting that serotonergic mechanisms may play a role in CM and its reversion to episodic migraine. Since the degree of post-treatment IDAP decrease is correlated with clinical improvement, IDAP might be potentially useful as an early predictor of GON-B efficacy.
