A Novel Regulatory Mechanism of Smooth Muscle α-actin Expression by NRG-1/circACTA2/miR-548f-5p Axis
Rationale: Neuregulin-1 (NRG-1) includes an extracellular EGF-like domain and an intracellular domain (NRG-1-ICD). In response to transforming growth factor (TGF)-β1，its cleavage by proteolytic enzymes releases a bioactive fragment, which suppresses the vascular smooth muscle cell (VSMC) proliferation by activating ErbB receptor. However, NRG-1-ICD function in VSMCs remains unknown.
Objective: Here, we characterize the function of NRG-1-ICD and underlying mechanisms in VSMCs.
Methods and Results: Immunofluorescence staining, Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR) showed that NRG-1 was expressed in rat, mouse and human VSMCs and was upregulated and cleaved in response to TGF-β1. In the cytoplasm of HASMCs, the NRG-1-ICD participated in filamentous actin formation by interacting with smooth muscle α-actin (α-SMA). In the nucleus, the Nrg-1-ICD induced circular ACTA2 (circACTA2) formation by recruitment of the zinc-finger transcription factor IKZF1 to the first intron of α-SMA gene. We further confirmed that circACTA2, acting as a sponge binding microRNA (miR)-548f-5p, interacted with miR-548f-5p targeting 3' untranslated region (3'-UTR) of α-SMA mRNA, which in turn relieves miR-548f-5p repression of the α-SMA expression and thus upregulates α-SMA expression, thereby facilitating stress fiber formation and cell contraction in HASMCs. Accordingly, in vivo studies demonstrated the localization of the interaction of circACTA2 with miR-548f-5p is significantly decreased in human intimal hyperplastic arteries compared with normal arteries, implicating that dysregulation of circACTA2 and miR-548f-5p expression is involved in intimal hyperplasia.
Conclusions: These results suggest that circACTA2 mediates NRG-1-ICD regulation of α-SMA expression in HASMCs via the NRG-1-ICD/circACTA2/miR-548f-5p axis. Our data provide a molecular basis for fine-turning α-SMA expression and VSMC contraction by transcription factor, circular RNA and microRNA.
- Received June 1, 2017.
- Revision received July 1, 2017.
- Accepted July 10, 2017.