RNA-binding protein complex LIN28/MSI2 enhances cancer stem cell-like properties by modulating Hippo-YAP1 signaling and independently of Let-7

Abstract

The RNA binding protein LIN28 directly modulates the stability and translation of target mRNAs independently of Let-7; however, the key downstream targets of LIN28 in this process are largely unknown. Here, we revealed that Hippo signaling effector YAP1 functioned as a key downstream regulator of LIN28 to modulate the cancer stem cell (CSC)-like properties and tumor progressions in triple negative breast cancer (TNBC). LIN28 was overexpressed in BC tissues and cell lines, and significantly correlated with poorer overall survivals in patients. Ectopic LIN28 expression enhanced, while knockdown of LIN28A inhibited the CSC-like properties, cell growth and invasive phenotypes of TNBC cells in vitro and in vivo. Transcriptome analysis demonstrated LIN28 overexpression significantly induced the expressions of YAP1 downstream genes, while reduced the transcripts of YAP1 upstream kinases, such as MST1/2 and LATS1/2, and knockdown of LIN28A exhibited the opposite effects. Furthermore, constitutive activation of YAP1 in LIN28 knockdown TNBC cells could rescue the cell growth and invasive phenotypes in vitro and in vivo. Mechanistically, instead of the dependence of Let-7, LIN28 recruited RNA binding protein MSI2 in a manner dependent on the LIN28 CSD domain and MSI2 RRM domain, to directly induce the mRNA decay of YAP1 upstream kinases, leading to the inhibition of Hippo pathway and activation of YAP1, which eventually gave rise to increased CSC populations, enhanced tumor cell growth and invasive phenotypes. Accordingly, co-upregulations of LIN28 and MSI2 in TNBC tissues were strongly associated with YAP1 protein level and tumor malignance. Taken together, our findings unravel a novel LIN28/MSI2-YAP1 regulatory axis to induce the CSC-like properties, tumor growth and metastasis, independently of Let-7, which may serve as a potential therapeutic strategy for the treatment of a subset of TNBC with LIN28 overexpression.

In Situ Transformable Supramolecular Nanomedicine Targeted Activating Hippo Pathway for Triple-Negative Breast Cancer Growth and Metastasis Inhibition

“…MDA-MB-231 cells at a density of 4 × 10 4 cells per well were seeded in 96-well dark plates and cultured until the cell density reached 80%. Next, the supernatant was removed and replaced with fresh medium containing different formulations with different concentrations (10,20,50,100,200, and 500 μM). The cells were then incubated for another 48 h. After PBS washing, centrifugation, and lysis, the HDAC activity in the cells of different groups was analyzed using a corresponding assay kit.…”

“…In particular, distant metastases, including brain, bone, and liver metastases, have become major obstacles to advanced TNBC therapy . Related studies have demonstrated that the YAP1 activation increases cancer-stem-cell (CSC)-like properties and tumor progression in TNBC, while a synergistic mTOR/Hippo-targeted combination therapy efficiently blocks TNBC tumor growth. , Additionally, the aberrant deregulation of the Hippo pathway could lead to the epithelial–mesenchymal transition (EMT), which is closely related to solid tumor metastasis and invasion, thus providing a promising therapeutic target for TNBC.…”

Research progress on RNA−binding proteins in breast cancer

“…Notably, LIN28 can also act as a transcription or translation regulator independent of let-7 ( 31 ). LIN28 recruit RNA binding protein Musashi-2 (MSI-2) by LIN28 CSD domain and MSI2 RRM domain, which directly induces the mRNA decay of YAP1 upstream kinase and negatively regulates Hippo pathway, resulting in the activation of YAP1, enhancing CSC like characteristics, tumorigenesis and metastasis in TNBC cells ( 32 ).…”

Tyrosine kinase SRC-mediated YAP1-KLF5 module regulates cancer stemness and metastasis in TNBC

“…Luciferase assay: luciferase assay was performed as previously described using a Dual-Luciferase Reporter Assay System (Promega) according to the manufacturer's instructions 31,32 . In detail, 8xGTIIC plasmid was used to detect the TEAD-associated transcriptional activity and Renilla plasmid was used as the internal transfection control, whereas the pGL3 empty vector was used as a negative control.…”

“…All the BC patients involved in this study provided an informed consent, and this study was ethically approved by the Ethics Committee of the Seventh Affiliated Hospital of Sun Yat-sen University. The IHC scores were calculated based on the percentage of positively-stained cells and staining intensity, as previously described 31 .…”