RNA-binding protein MSI2 isoforms expression and regulation in progression of triple-negative breast cancer

Abstract

Background: The RNA-binding protein Musashi-2 (MSI2) has been implicated in the tumorigenesis and tumor progression of some human cancers. MSI2 has also been reported to suppress tumor epithelial-to-mesenchymal transition (EMT) progression in breast cancer, and low MSI2 expression is associated with poor outcomes for breast cancer patients; however, the underlying mechanisms have not been fully investigated. This study investigated the expression and phenotypic functions of two major alternatively spliced MSI2 isoforms (MSI2a and MSI2b) and the potential molecular mechanisms involved in triple-negative breast cancer (TNBC) progression. Methods: The Illumina sequencing platform was used to analyze the mRNA transcriptomes of TNBC and normal tissues, while quantitative reverse transcription-polymerase chain reaction and immunohistochemistry validated MSI2 isoform expression in breast cancer tissues. The effects of MSI2a and MSI2b on TNBC cells were assayed in vitro and in vivo. RNA immunoprecipitation (RIP) and RNA sequencing were performed to identify the potential mRNA targets of MSI2a, and RIP and luciferase analyses were used to confirm the mRNA targets of MSI2. Results: MSI2 expression in TNBC tissues was significantly downregulated compared to that in normal tissues. In TNBC, MSI2a expression was associated with poor overall survival of patients. MSI2a overexpression in vitro and in vivo inhibited TNBC cell invasion as well as extracellular signal-regulated kinase 1/2 (ERK1/2) activity. However, MSI2b overexpression had no significant effects on TNBC cell migration. Mechanistically, MSI2a expression promoted TP53INP1 mRNA stability by its interaction with the 3′-untranslated region of TP53INP1 mRNA. Furthermore, TP53INP1 knockdown reversed MSI2a-induced suppression of TNBC cell invasion, whereas ectopic expression of TP53INP1 and inhibition of ERK1/2 activity blocked MSI2 knockdown-induced TNBC cell invasion. Conclusions: The current study demonstrated that MSI2a is the predominant functional isoform of MSI2 proteins in TNBC, that its downregulation is associated with TNBC progression and poor prognosis and that MSI2a expression inhibited TNBC invasion by stabilizing TP53INP1 mRNA and inhibiting ERK1/2 activity. Overall, our study provides new insights into the isoform-specific roles of MSI2a and MSI2b in the tumor progression of TNBC, allowing for novel therapeutic strategies to be developed for TNBC.

Systematic Construction and Validation of an RNA Binding Proteins-Based Signature for Prognostic Prediction in Gastric Cancer

“…Many RBPs bind to sequence-speci c motifs or RNA secondary structures through unique modular arrangements of individual RNA-binding domains to play the roles in the homeostatic regulation of gene expression [24,25], which in uence the progression of many diseases. For example, RBP MSI2a expression alleviates triple-negative breast cancer invasive abilities through stabilizing TP53INP1 mRNA and inhibiting ERK1/2 activity [26]. RBP CASC9 interacts with hnRNPL form a complex to regulate DNA damage signal and PI3K/AKT signaling pathway, in uencing tumor cell proliferation and apoptosis in vivo [27].…”

Potential Role of Musashi-2 RNA-Binding Protein in Cancer EMT

“…The MSI2 gene, physically located on chromosome 17q22, 10 produces four mRNA transcripts, resulting in 4 corresponding protein isoforms (MSI2a, MSI2b, MSI2c, MSI2d). 23 All of these four isoforms contain two conserved N-terminal RNA-recognition motifs (RRM1 and RRM2) but differ in the N-terminal or C-terminal amino acids. Biochemical and structural studies showed that the RRM1 contributes to the majority of the binding energy and specificity, while RRM2 has a more supportive role.…”

“…In addition, the effect of MSI2 in regulating specific mRNA translation differs depending on MSI2 protein isoforms, phosphorylation status, and cellular context. 23,[30][31][32][33] For example, Li et al demonstrated that overexpression of MSI2a in TNBC cells inhibits EMT, while MSI2b shows no significant effect in TNBC progression. 23 Similarly, ectopic expression of MSI2a, but not MSI2b, enhances the self-renewal capacity of embryonic stem cells (ESCs).…”

“…23,[30][31][32][33] For example, Li et al demonstrated that overexpression of MSI2a in TNBC cells inhibits EMT, while MSI2b shows no significant effect in TNBC progression. 23 Similarly, ectopic expression of MSI2a, but not MSI2b, enhances the self-renewal capacity of embryonic stem cells (ESCs). 30 MacNicol et al demonstrated that the canonical MSI2a is subject to site-specific phosphorylation at C-terminus, converting MSI2 from a translational repressor to an activator, while the truncated isoform of human MSI2b that lacks regulatory phosphorylation sites fails to promote translation of target mRNAs.…”

“…61 MSI2a is significantly downregulated in TNBC tumors, which is associated with a higher histological grade and poor prognosis. 23 Table 2 lists the clinical significance of MSI2 expression that has been reported.…”