VGLL1 stabilization of cytoplasmic TAZ promotes EGFR expression and maintains tumor initiating cells in breast cancer independent of TEAD

Vestigial-like family member 1 (VGLL1) is one of the X-linked genes whose expression is elevated in basal-like breast cancer (BLBC) because of X-chromosome isodisomy. As an approach towards understanding its function, we performed correlation study using transcript data of breast cancer patients from cBioPortal for Cancer Genomics. Our analysis identified EGFR as the most correlated transcript with VGLL1. We demonstrate that VGLL1 promotes EGFR expression and increases the frequency of breast tumor initiating cells (CD44high/+CD24low/-). These findings are crucial because an elevated EGFR expression and high frequency of CD44high/+CD24low/- cells are defining features of BLBC, and we provide a new mechanistic insight into how their expressions are controlled. Importantly, VGLL1 regulation of EGFR and CD44high/+CD24low/- population is mediated by the hippo-transducer TAZ which exerts its oncogenic roles by binding and activating TEAD transcription factors. A crucial finding is that TEAD-binding domain of TAZ is dispensable for its regulation of EGFR and CD44high/+CD24low/- cells. Instead, VGLL1 stabilization of cytoplasmic TAZ is essential for these functions. Also, we show that VGLL1/TAZ restricts the surface expression of CD24 which contributes to the increased number of CD44high/+CD24low/- cells. In addition, we observed that VGLL1 represses AXL expression and suppresses claudin-low phenotype, and that is caused by the VGLL1 mediated nuclear expulsion of TAZ. Therefore, EGFR and AXL seem to represent two different breast tumor subtypes, and their differential expressions is controlled by VGLL1.

The opposite effects of VGLL1 and VGLL4 genes on granulosa cell proliferation and apoptosis of hen ovarian prehierarchical follicles

Transcription cofactors Vestigial like family (VGLL) members consisting of four homologs (VGLL1-4) are associated with cell growth and metastasis in mammals, among which VGLL1 gene has been documented to possess tumorigenic functions in various types of tumor, and VGLL4 acts as a new tumor suppressor; likewise several studies indicated that they potentially play a role in the regulation of ovary growth and function. However, the biological effects of chicken VGLL1 and VGLL4 on the proliferation, apoptosis, and steroidogenesis of the granulosa cells (GCs) during ovarian follicle development remain unknown now. This study found that VGLL1 and VGLL4 genes present divergent expression patterns of the transcripts in the GCs of various sized prehierarchical follicles (PFs) before follicle selection. Specific small interfering RNA (siRNA) was employed to elucidate the exact roles of VGLL1 and VGLL4 in regulating the PF development of the hen ovary. The results demonstrated that the mRNA expression levels of the steroidogenic-related enzyme steroidogenic acute regulatory protein (STAR) gene and the cell proliferation-related factors B-cell lymphoma-2 (BCL2), and cyclin D1 (CCND1) genes were significantly down-regulated in the cells with VGLL1 silence but remarkably up-regulated in the cells lacking VGLL4. Whereas the expression level of the cell apoptosis biomarker caspase-3 (CASP3) transcript was noticeably enhanced in the GCs without VGLL1 but significantly decreased in the GCs deprived of VGLL4. Further results showed that the siRNA-mediated silence of VGLL1 caused a significant increase in apoptosis with a reduction in the proliferation of GCs. Nevertheless, knockdown of VGLL4 resulted in a remarkable decrement in apoptosis but a memorable augment in proliferation of the GCs. Taken together, this study proved that VGLL1 promotes cell proliferation and steroidogenesis but inhibits apoptosis. In contrast, VGLL4 stimulates GC apoptosis while suppressing the GC proliferation and steroidogenesis in the hen ovarian follicles. We conluded that VGLL1 and VGLL4 affect oppositely the ovarian prehierarchical follicle development by the different regulatory manner in the GC proliferation and apoptosis of chicken ovary.

VGLL1 phosphorylation and activation promotes gastric cancer malignancy via TGF-β/ERK/RSK2 signaling

We previously reported that vestigial-like 1 (VGLL1), a cofactor of transcriptional enhanced associate domain 4 (TEAD4), is transcriptionally regulated by PI3K and β-catenin signaling and is involved in gastric cancer malignancy. However, the precise mechanism underlying the regulation of VGLL1 activation remains unknown. Therefore, we aimed to investigate the molecular mechanism underlying the transforming growth factor-β (TGF-β)-mediated activation of VGLL1 and the VGLL1-TEAD4 interaction in gastric cancer cells. We showed that TGF-β enhanced VGLL1 phosphorylation and that this phosphorylated VGLL1 functioned as a transcription cofactor of TEAD4 in NUGC3 cells. TGF-β also increased the phosphorylation of ERK and ribosomal S6 kinase 2 (RSK2) in NUGC3 cells, thereby triggering the translocation of phosphorylated RSK2 to the nucleus. Site-directed mutagenesis and immunoprecipitation experiments revealed that RSK2 phosphorylated VGLL1 at S84 in the presence of TGF-β. Mutation of VGLL1 at S84 suppressed VGLL1-TEAD4 binding and the subsequent transcriptional activation of matrix metalloprotease 9 (MMP9). Moreover, VGLL1 peptide containing S84 suppressed the TGF-β-induced MMP9 expression and reduced the invasion and proliferation of gastric cancer cells, whereas VGLL1 peptide containing S84A did not. Furthermore, suppression of expression or activation of VGLL1 enhances the therapeutic effects of lapatinib. Collectively, these results indicate that VGLL1 phosphorylation via TGF-β/ERK/RSK2 signaling plays a crucial role in MMP9-mediated malignancy of gastric cancer. In addition, our study highlights the therapeutic potential of the peptide containing VGLL1 S84 for the treatment of gastric cancer.

PI3K/AKT/β-Catenin Signaling Regulates Vestigial-Like 1 Which Predicts Poor Prognosis and Enhances Malignant Phenotype in Gastric Cancer

Although gastric cancer is a common cause of cancer mortality worldwide, its biological heterogeneity limits the available therapeutic options. Therefore, identifying novel therapeutic targets for developing effective targeted therapy of gastric cancer is a pressing need. Here, we investigate molecular function and regulatory mechanisms of Vestigial-like 1 (VGLL1) in gastric cancer. Microarray analysis of 556 gastric cancer tissues revealed that VGLL1 was a prognostic biomarker that correlated with PI3KCA and PI3KCB. VGLL1 regulates the proliferation of gastric cancer cells, as shown in live cell imaging, sphere formation, and in vivo xenograft model. Tail vein injection of NUGC3 cells expressing shVGLL1 resulted in less lung metastasis occurring when compared to the control. In contrast, larger metastatic lesions in lung and liver were detected in the VGLL1-overexpressing NUGC3 cell xenograft excision mouse model. Importantly, VGLL1 expression is transcriptionally regulated by the PI3K-AKT-β-catenin pathway. Subsequently, MMP9, a key molecule in gastric cancer, was explored as one of target genes that were transcribed by VGLL1-TEAD4 complex, a component of the transcription factor. Taken together, PI3K/AKT/β-catenin signaling regulates the transcription of VGLL1, which promotes the proliferation and metastasis in gastric cancer. This finding suggests VGLL1 as a novel prognostic biomarker and a potential therapeutic target.