Interaction between STAT3 and GLI1/tGLI1 oncogenic transcription factors promotes the aggressiveness of triple-negative breast cancers and HER2-enriched breast cancer

Abstract

STAT3, GLI1, and truncated GLI1 (tGLI1) are oncogenic transcription factors playing important roles in breast cancer. tGLI1 is a gain-of-function GLI1 isoform. Whether STAT3 physically and/or functionally interacts with GLI1/tGLI1 has not been explored. To address this knowledge gap, we analyzed 47 node-positive breast cancer specimens using immunohistochemical staining and found that p-STAT3 (Y705), GLI1, and tGLI1 are co-overexpressed in the majority of triple-negative (64%) and HER2-enriched (68%) breast carcinomas, and in lymph node metastases (65%). Using Gene Set Enrichment Analysis, we analyzed 710 breast tumors and found that STAT3- and GLI1/tGLI1-activation signatures are co-enriched in triple-negative and HER2-enriched, but not in luminal subtypes of breast cancers. Patients with high levels of STAT3 and GLI1/tGLI1 co-activation in their breast tumors had worse metastasis-free survival compared to those with low levels. Since these proteins co-overexpress in breast tumors, we examined whether they form complexes and observed that STAT3 interacted with both GLI1 and tGLI1. We further found that the STAT3-GLI1 and STAT3-tGLI1 complexes bind to both consensus GLI1- and STAT3-binding sites using chromatin immunoprecipitation (ChIP) assay, and that the co-overexpression markedly activated a promoter controlled by GLI1-binding sites. To identify genes that can be directly co-activated by STAT3 and GLI1/tGLI1, we analyzed three ChIP-Seq datasets and identified 36 potential target genes. Following validations using RT-PCR and survival analysis, we identified three genes as novel transcriptional targets of STAT3 and GLI1/tGLI1, R-Ras2, Cep70, and UPF3A. Finally, we observed that co-overexpression of STAT3 with GLI1/tGLI1 promoted the ability of breast cancer cells to form mammospheres and that STAT3 only cooperates with tGLI1 in immortalized mammary epithelial cells. In summary, our study identified novel physical and functional cooperation between two families of oncogenic transcription factors, and the interaction contributes to aggressiveness of breast cancer cells and poor prognosis of triple-negative and HER2-enriched breast cancers.

TGLI1 transcription factor mediates breast cancer brain metastasis via activating metastasis-initiating cancer stem cells and astrocytes in the tumor microenvironment

“…TGLI1 is an alternatively spliced variant of GLI1, as a result of a 41 amino acid in-frame deletion, which retains all of the functional domains as GLI1, and is activated by the Shh-PTCH1-SMO signaling axis 8 . We have shown that TGLI1 is expressed in GBM and breast cancer, but is not expressed in normal brain or breast tissue 5,8,9,11 . Consistent with our findings, TGLI1 was reported to be expressed in highly invasive hepatocellular carcinoma but is not detected in normal hepatocytes 12 .…”

<p>Functions and Clinical Significance of UPF3a Expression in Human Colorectal Cancer</p>

“…10 Sirkisoon et al have demonstrated that the expression of UPF3a can be elevated by upregulating STAT3 and GLI1/ tGLI1, suggesting that UPF3a acts as an oncogene in triple-negative breast cancers and HER2-enriched breast cancer. 11 Furthermore, Popp et al have reported that NMD eliminates mutated mRNAs that fail to function in a dominant-negative manner, but are partially functional and could help prevent cancer initiation. 21 UPF3a is unique among genes engaging in the NMD pathway and the GCR, possibly playing a balanced role within these two pathways.…”

“…9,10 Moreover, Sirkisoon et al have suggested that STAT3 and GLI1/tGLI1, both oncogenic transcription factors, enhance the aggressiveness of triple-negative breast cancers and HER2-enriched breast cancer by upregulating UPF3a expression. 11 Remarkably, distant tumor metastases affect patient prognosis. 12 Nevertheless, UPF3a participated in both NMD and GCR pathways in tumor; however, the association with patient prognosis in CRC remains poorly investigated.…”

Somatic mutations in genes associated with mismatch repair predict survival in patients with metastatic cancer receiving immune checkpoint inhibitors

“…Glioma oncogene homolog 1 (GLI1) is an oncogenic transcription factor playing important roles in cancer. Patients with GLI1 activation and breast tumors had worse metastasis-free survival compared with those with low levels (37). The association between the aforementioned gene variants and the efficacy of immunologic checkpoint inhibitors is not clear and needs to be further verified.…”