5'isomiR-183-5p|+2 elicits tumor suppressor activity in a negative feedback loop with E2F1.

BACKGROUND: MicroRNAs (miRNAs) and isomiRs play important roles in tumorigenesis as essential regulators of gene expression. 5'isomiRs exhibit a shifted seed sequence compared to the canonical miRNA, resulting in different target spectra and thereby extending the phenotypic impact of the respective common pre-miRNA. However, for most miRNAs, expression and function of 5'isomiRs have not been studied in detail yet. Therefore, this study aims to investigate the functions of miRNAs and their 5'isomiRs. METHODS: The expression of 5'isomiRs was assessed in The Cancer Genome Atlas (TCGA) breast cancer patient dataset. Phenotypic effects of miR-183 overexpression in triple-negative breast cancer (TNBC) cell lines were investigated in vitro and in vivo by quantifying migration, proliferation, tumor growth and metastasis. Direct targeting of E2F1 by miR-183-5p|+2 was validated with a 3'UTR luciferase assay and linked to the phenotypes of isomiR overexpression. RESULTS: TCGA breast cancer patient data indicated that three variants of miR-183-5p are highly expressed and upregulated, namely miR-183-5p|0, miR-183-5p|+1 and miR-183-5p|+2. However, TNBC cell lines displayed reduced proliferation and invasion upon overexpression of pre-miR-183. While invasion was reduced individually by all three isomiRs, proliferation and cell cycle progression were specifically inhibited by overexpression of miR-183-5p|+2. Proteomic analysis revealed reduced expression of E2F target genes upon overexpression of this isomiR, which could be attributed to direct targeting of E2F1, specifically by miR-183-5p|+2. Knockdown of E2F1 partially phenocopied the effect of miR-183-5p|+2 overexpression on cell proliferation and cell cycle. Gene set enrichment analysis of TCGA and METABRIC patient data indicated that the activity of E2F strongly correlated with the expression of miR-183-5p, suggesting transcriptional regulation of the miRNA by a factor of the E2F family. Indeed, in vitro, expression of miR-183-5p was regulated by E2F1. Hence, miR-183-5p|+2 directly targeting E2F1 appears to be part of a negative feedback loop potentially fine-tuning its activity. CONCLUSIONS: This study demonstrates that 5'isomiRs originating from the same arm of the same pre-miRNA (i.e. pre-miR-183-5p) may exhibit different functions and thereby collectively contribute to the same phenotype. Here, one of three isomiRs was shown to counteract expression of the pre-miRNA by negatively regulating a transcriptional activator (i.e. E2F1). We speculate that this might be part of a regulatory mechanism to prevent uncontrolled cell proliferation, which is disabled during cancer progression.

Complete atrioventricular septal defect and pulmonary stenosis diagnosed in a 49-year-old woman after 10 uneventful births.

Atrioventricular septal defects constitute 4% of all congenital cardiac malformations. Patients with complete atrioventricular septal defect rarely survive for decades without surgical treatment. Pulmonary stenosis can provide a delicate balance between the pulmonary and systemic circulations and thereby increase longevity. We present the case of a 49-year-old woman whose complete atrioventricular septal defect and associated pulmonary stenosis were diagnosed only after she had given birth to 10 live children through uneventful spontaneous delivery. We discuss her successful surgical treatment in terms of the available medical literature.

Atrial fibrillation in a healthy adolescent after heavy smoking of contraband cigarettes.

The use of contraband cigarettes is a serious public health problem. We present a case of atrial fibrillation in a healthy adolescent suspected to be caused by smoking contraband cigarettes. A 15-year-old man was admitted to our emergency department experiencing syncope and palpitations. He was a cigarette smoker, but he had never smoked any illicit tobacco products before. He had finished a pack of counterfeit cigarettes (20 pieces) in 1.5 h. His electrocardiogram showed atrial fibrillation with a rapid ventricular response and irregular RR intervals. The patient had no history of alcohol use, surgery, palpitations, hypertension, chronic bronchitis, or any infectious diseases. His atrial fibrillation was converted to a normal sinus rhythm after the cardioversion treatment. Our patient was discharged from the pediatric cardiology service and advised to quit smoking cigarettes, strictly warning against illicit tobacco products. In conclusion, intensive smoking of counterfeit cigarettes may lead to occurrences of atrial fibrillation.

Myocardial bridging in a child with hypertrophic obstructive cardiomyopathy.

Myocardial bridging (MB) is a rare coronary anomaly in children which is typically associated with hypertrophic obstructive cardiomyopathy (HCM) or left ventricular hypertrophy. Hypertrophic obstructive cardiomyopathy is the leading cause of sudden cardiac death in young patients, and the association of myocardial ischemia with sudden death has been recognized in patients with HCM. In this report, we describe an 11-year-old boy presented with a history of exertional, nonspecific chest pain and palpitations. Cardiac catheterization revealed MB of the left anterior descending coronary artery with evidence of intramyocardial obstruction during systole. Surgical unroofing of the affected coronary artery segment resulted in complete recovery. Myocardial bridging should be included in the differential diagnosis of children presenting with signs of ischemia.