Alternative Processing of the U2 Small Nuclear RNA Produces a 19–22nt Fragment with Relevance for the Detection of Non-Small Cell Lung Cancer in Human Serum

Abstract

RNU2 exists in two functional forms (RNU2-1 and RNU2-2) distinguishable by the presence of a unique 4-bases motif. Detailed investigation of datasets obtained from deep sequencing of five human lung primary tumors revealed that both forms express at a high rate a 19–22nt fragment (miR-U2-1 and -2) from its 3′ region and contains the 4-bases motif. Deep sequencing of independent pools of serum samples from healthy donors and lung cancer patients revealed that miR-U2-1 and -2 are pervasively processed in lung tissue by means of endonucleolytic cleavages and stably exported to the blood. Then, microarrays hybridization experiments of matched normal/tumor samples revealed a significant over-expression of miR-U2-1 in 14 of 18 lung primary tumors. Subsequently, qRT-PCR of miR-U2-1 using serum from 62 lung cancer patients and 96 various controls demonstrated that its expression levels identify lung cancer patients with 79% sensitivity and 80% specificity. miR-U2-1 expression correlated with the presence or absence of lung cancer in patients with chronic obstructive pulmonary disease (COPD), other diseases of the lung – not cancer, and in healthy controls. These data suggest that RNU2-1 is a new bi-functional ncRNA that produces a 19–22nt fragment which may be useful in detecting lung cancer non-invasively in high risk patients.

Circulating U2 Small Nuclear RNA Fragments as a Novel Diagnostic Tool for Patients with Epithelial Ovarian Cancer

“…In the present investigation, we observed significantly increased RNU2-1f concentrations in the patients' blood. This is in accordance with previous studies in serum from colorectal, pancreatic, esophageal, and lung cancer patients, likewise reporting RNU2-1f concentrations to be increased in the circulation of cancer patients (16,18,21 ). Consequently, an increased abundance of RNU2-1f in the blood of cancer patients seems to be a more general phenomenon, and its clinical utility in terms of a blood-based biomarker thereby may apply to a broader spectrum of malignancies of different origin.…”

“…This finding is comparable to a previous study on esophageal squamous cell carcinoma, showing a discrimination of tumor patients and healthy controls with an AUC value of 0.75 (21 ). However, for patients with gastrointestinal or lung cancer, circulating RNU2-1f enabled more accurate discrimination (AUC 0.97 and 0.87, respectively) (16,18 ). On the basis of our present findings, we consider serum RNU2-1f a suboptimal candidate for an ovarian cancer screening tool.…”

“…Importantly, given that the putative miR-1246 is very likely a result of false mapping of RNU2-1f, all of the results reported herein concern circulating RNU2-1f rather than miR-1246 (16,18 ). In the present investigation, we observed significantly increased RNU2-1f concentrations in the patients' blood.…”

“…One hypothesis supposes RNU2-1f to be encapsulated into apoptotic bodies and to be unspecifically released into the bloodstream in the course of apoptotic degradation (16 ). Conversely, an alternative processing mechanism has recently been discussed, producing full-size RNU2-1 on the one hand and RNU2-1f on the other hand (18 ). Following this theory, RNU2-1f is supposed to be stably and selectively transported into the bloodstream (18,21,25 ).…”

“…Conversely, an alternative processing mechanism has recently been discussed, producing full-size RNU2-1 on the one hand and RNU2-1f on the other hand (18 ). Following this theory, RNU2-1f is supposed to be stably and selectively transported into the bloodstream (18,21,25 ). Moreover, the fact that circulating RNU2-1f concentration is highly increased in tumorbearing patients might be functionally connected to a concomitant upregulation of full-length RNU2-1 in the primary tumor, which we confirmed in the present study.…”