Transcription activation of circ-STAT3 induced by Gli2 promotes the progression of hepatoblastoma via acting as a sponge for miR-29a/b/c-3p to upregulate STAT3/Gli2

Abstract

Background: Hepatoblastoma (HB) is a common liver malignancy in children. Our previous study has disclosed the crucial role of STAT3 (signal transducer and activator of transcription 3) in HB. Aim of the study: Present study was designed to study the circular RNA (circRNA) STAT3 in HB. Methods: Gel electrophoresis revealed the circular characteristics of circ-STAT3. Function assays like EdU, transwell and sphere formation assay disclosed the function of circ-STAT3 in HB cells. Mechanism assays including ChIP, RIP, RNA pull down assay demonstrated the macular mechanism underlying circ-STAT3. Results: Circ_0043800, which was originated from STAT3, was up-regulated in HB tissues and cells. More importantly, silencing of circ-STAT3 led to the inhibition on HB cell growth, migration and stem-cell characteristics. Circ_0043800 was predominantly located in the cytoplasm of HB cells. Then, circ_0043800 was found to upregulate STAT3 via sponging miR-29a/b/c-3p. Besides, we identified that STAT3 overexpression partially rescued silenced circ_0043800, while miR-29a/b/c-3p inhibition completely rescued silenced circ_0043800 on HB cellular biological behaviors. Subsequently, Gli2 (GLI family zinc finger 2) was identified as another target of miR-29a/b/c-3p. Circ_0043800 served as a competing endogenous RNA (ceRNA) to up-regulate both Gli2 and STAT3 via sponging miR-29a/b/c-3p. Moreover, we figured out that Gli2 overexpression completely rescued silenced circ_0043800 on HB cell malignant behaviors. After that, we discovered that Gli2 transcriptionally activated circ_0043800. The in-vivo assays further revealed that circ_0043800 promoted HB tumor growth by up-regulation of Gli2 and STAT3. Conclusion: Gli2-induced circ_0043800 served as the ceRNA to promote HB by up-regulation of STAT3 and Gli2 at a miR-29a/b/c-3p dependent manner.

Circular RNAs: Emerging Regulators of the Major Signaling Pathways Involved in Cancer Progression

“…Another feedback interaction was also reported in hepatoblastoma [ 130 ]. In particular, circ-STAT3 is transcriptionally activated by GLI2, and at the same time, GLI2 and STAT3 are both upregulated due to circ-STAT3 binding miR-29-3p isomiRs.…”

“…Moreover, an increasing number of studies emphasize the participation of circRNAs in the regulation of signaling pathways linked to cancer stem cells (CSCs) [ 130 ]. CSCs are vital for tumor progression, since they promote growth and are responsible for metastatic spread, relapses, and treatment failure.…”

Targeting STAT3 in Cancer Immunotherapy

“…In general, circular RNAs (circRNAs) can modulate gene expression by acting as sponges of endogenous miRNAs. It has shown that circ-HIPK3, circ_0076305 and circ-STAT3 positively modulate STAT3 signaling by sponging miR-124-3p, miR-296-5p, and miR-29a/b/c-3p, respectively [ 36 – 38 ]. In parallel, STAT3 has a capacity of regulating ncRNAs directly or indirectly.…”

Circular RNA: an important player with multiple facets to regulate its parental gene expression

“…15 Recent studies have shown that several cytoplasmic circRNAs can regulate the expression of transcriptional factors. [26][27][28] A study in 2018 showed that circITGA7 could promote the transcription of its host gene ITGA7 by suppressing the transcription factor RREB1 via the Ras pathway. 26 Chia et al 27 have suggested that circ-DAB1 upregulates the expression of recombination signal-binding protein for the immunoglobulin kappa J region (RBPJ), an important transcriptional factor in the NOTCH pathway, to activate the parental gene DAB1 transcription.…”

“…52 More recently, circ-STAT3 was also found to elevate STAT3 expres-sion by upregulating the transcription factor Gli2 via sponging miR-29a/b/c-3p. 28 Studies cited above illustrate that circRNA can regulate the transcription of its parental gene and impact distinct steps in the transcription cycle. Given that both cytoplasmic and nuclear circRNAs are involved, transcriptional control could represent a more general role of circRNAs than is currently appreciated.…”