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HuR enhances FSTL1 transcript stability to promote invasion and metastasis of squamous cell carcinoma.

ABSTRACT: Squamous cell carcinoma (SCC) is a lethal malignancy with a high propensity for metastasis. Follistatin-like 1 (FSTL1), a pro-metastatic glycoprotein, is absent from healthy epithelia and aberrantly upregulated in SCC. The FSTL1 transcript encodes two alternative gene products whose dominance is post-transcriptionally regulated via a bistable switch. In healthy epithelia, FSTL1 mRNA is destabilized by binding of KH-type splicing regulatory protein (KSRP), and processed as a primary microRNA encoding miR-198. In SCC, KSRP downregulation terminates miR-198 processing, enabling FSTL1 translation. Here, we identify HuR (Human Antigen R) as an upstream regulator of FSTL1 and describe how downregulation of KSRP is permissive, but not sufficient, to promote sustained FSTL1 expression. Moreover, we demonstrate how the interplay between two RNA-binding proteins controls the translation of pro-oncogenic FSTL1. Increased expression of HuR in SCC outcompetes KSRP and enhances FSTL1 transcript stability, enabling persistent FSTL1 expression and activation of downstream metastatic pathways.

SUBMITTER: Sundaram GM

PROVIDER: S-EPMC8569354 | biostudies-literature | 2021

REPOSITORIES: biostudies-literature

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HuR enhances FSTL1 transcript stability to promote invasion and metastasis of squamous cell carcinoma.

Sundaram Gopinath M GM Quah Shan S Guang Lum Guo LG Sampath Prabha P

American journal of cancer research 20211015 10

Squamous cell carcinoma (SCC) is a lethal malignancy with a high propensity for metastasis. Follistatin-like 1 (FSTL1), a pro-metastatic glycoprotein, is absent from healthy epithelia and aberrantly upregulated in SCC. The <i>FSTL1</i> transcript encodes two alternative gene products whose dominance is post-transcriptionally regulated via a bistable switch. In healthy epithelia, <i>FSTL1 mRNA</i> is destabilized by binding of KH-type splicing regulatory protein (KSRP), and processed as a primary ...[more]

PMID: 34765305

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Project description:BackgroundThe mechanisms underlying the occurrence and development of esophageal squamous cell carcinoma (ESCC) remains to be elucidated. The present study aims to investigate the roles and implications of IGF2BP1 overexpression in ESCC.MethodsIGF2BP1 protein expression in ESCC samples was assessed by immunohistochemistry (IHC), and the mRNA abundance of IGF2BP1 and INHBA was analyzed with TCGA datasets and by RNA in situ hybridization (RISH). The methylation level of the IGF2BP1 promoter region was detected by methylation-specific PCR (MSP-PCR). Cell viability, migration, invasion and in vivo metastasis assays were performed to explore the roles of IGF2BP1 overexpression in ESCC. RNA immunoprecipitation sequencing (RIP-seq) and mass spectrometry were applied to identify the target RNAs and interacting proteins of IGF2BP1, respectively. RIP-PCR, RNA pulldown, immunofluorescence (IF), gene-specific m6A PCR and RNA stability assays were used to uncover the molecular mechanisms underlying the malignant phenotypes of ESCC cells caused by IGF2BP1 dysregulation. BTYNB, a small molecular inhibitor of IGF2BP1, was evaluated for its inhibitory effect on the malignant phenotypes of ESCC cells.ResultsIGF2BP1 overexpression was detected in ESCC tissues and associated with the depth of tumor invasion. In addition, IGF2BP1 mRNA expression in ESCC cells was negatively correlated with the level of its promoter methylation. Knockdown of IGF2BP1 inhibited ESCC cell invasion and migration as well as tumor metastasis. Mechanistically, we observed that IGF2BP1 bound and stabilized INHBA mRNA and then resulted in higher protein expression of INHBA, leading to the activation of Smad2/3 signaling, thus promoting malignant phenotypes. The mRNA level of INHBA was upregulated in ESCC tissues as well. Furthermore, IGF2BP1 interacted with G3BP stress granule assembly factor 1 (G3BP1). Knockdown of G3BP1 also down-regulated the INHBA-Smad2/3 signaling. BTYNB abolished this activated signaling and significantly attenuated the malignant phenotypes of ESCC cells.ConclusionsElevated expression of IGF2BP1 is a frequent event in ESCC tissues and might be a candidate biomarker for the disease. IGF2BP1 overexpression promotes the invasion and migration of ESCC cells by activating the INHBA-Smad2/3 pathway, providing a potential therapeutic target for ESCC patients with high expression of IGF2BP1.

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HuR enhances FSTL1 transcript stability to promote invasion and metastasis of squamous cell carcinoma.

Publications

HuR enhances FSTL1 transcript stability to promote invasion and metastasis of squamous cell carcinoma.

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