Mammalian MST2 kinase and human Salvador activate and reduce estrogen receptor alpha in the absence of ligand

STK3 higher expression association with clinical characteristics in intrinsic subtypes of breast cancer invasive ductal carcinoma patients

PURPOSE

STK3 has a central role in maintaining cell homeostasis, proliferation, growth, and apoptosis. Previously, we investigated the functional link between STK3/MST2, and estrogen receptor in MCF-7 breast cancer cells. To expand the investigation, this study evaluated STK3's higher expression and associated genes in breast cancer intrinsic subtypes using publicly available data.

METHODS

The relationship between clinical pathologic features and STK3 high expression was analyzed using descriptive and multivariate analysis.

RESULTS

Increased STK3 expression in breast cancer was significantly associated with higher pathological cancer stages, and a different expression level was observed in the intrinsic subtypes of breast cancer. Kaplan-Meier analysis showed that breast cancer with high STK3 had a lower survival rate in IDC patients than that with low STK3 expression (p < 0.05). The multivariate analysis unveiled a strong correlation between STK3 expression and the survival rate among IDC patients, demonstrating hazard ratios for lower expression. In the TCGA dataset, the hazard ratio was 0.56 (95% CI 0.34-0.94, p = 0.029) for patients deceased with tumor, and 0.62 (95% CI 0.42-0.92, p = 0.017) for all deceased patients. Additionally, in the METABRIC dataset, the hazard ratio was 0.76 (95% CI 0.64-0.91, p = 0.003) for those deceased with tumor. From GSEA outcomes 7 gene sets were selected based on statistical significance (FDR < 0.25 and p < 0.05). Weighted Sum model (WSM) derived top 5% genes also have higher expression in basal and lower in luminal A in association with STK3.

CONCLUSION

By introducing a novel bioinformatics approach that combines GSEA and WSM, the study successfully identified the top 5% of genes associated with higher expression of STK3.

Serine/Threonine Protein Kinase-3 Promotes Oral Squamous Cell Carcinoma by Activating Ras-MAPK Mediated Cell Cycle Progression

Purpose

Serine/threonine protein kinase-3 (STK3) is a key molecule in the Hippo pathway, but its biological function in the development of oral squamous cell carcinoma (OSCC) remains unclear, we explored the roles of STK3 in OSCC.

Methods

In this study, GEPIA was used to analyse STK3 expression in different types of tumor patients. OSCC patients were then collected from Liaocheng People's Hospital (Shandong, China), to further detect STK3 expression by qRT-PCR and Western blotting. To explore the function of STK3, overexpression and knockdown experiment were designed. Cell proliferation, migration and invasion were analyzed.

Results

First, STK3 is significantly up-regulated in OSCC patients, and high STK3 expression is associated with poor prognosis. Then, in vitro cell proliferation, migration, and invasion tests were used to determine the role of STK3. STK3 overexpression significantly promoted the proliferation, migration and invasion of OSCC cells. The downregulation of STK3 inhibited the proliferation, migration and invasion of OSCC cells. Finally, STK3 was demonstrated to promote oral squamous cell carcinoma by activating Ras-MAPK mediated cell cycle progression.

Conclusion

The results showed that STK3 was a potential cancer promoter for OSCC. It plays an important role in promoting the progression of oral squamous cell carcinoma. Inhibition of STK3 may prove beneficial as a therapeutic strategy for OSCC treatment.

Hypoxic induction of apoptosis occurs through HIF-1α and accompanies mammalian sterile 20-like kinase 2 cleavage in human endometrial adenocarcinoma Ishikawa cells

The incidence of endometrial cancer is increasing worldwide. One of the main causes of this cancer is a hormone imbalance; progesterone derivatives have been used for treatment. However, reports have shown that hypoxia plays important and possibly beneficial roles in endometrial function. Here, we show the effect of hypoxia on the proliferation of human endometrial adenocarcinoma Ishikawa cells. Hypoxia induced caspase-dependent apoptosis in Ishikawa cells. Overexpression and siRNA-mediated knockdown of hypoxia-inducible factor-1α (HIF-1α) confirmed that HIF-1α accelerates hypoxia-induced cell death. Treatment with dimethyloxalglycine, which stabilizes HIF-1α, suppressed cell proliferation. Kaplan-Meier analysis showed that the expression level of HIF-1α has a significant positive effect on the survival rate of endometrial cancer patients. In our search for cellular targets involved in hypoxic apoptosis, we noticed that mammalian sterile 20-like kinase 2 (MST2), a member of the Hippo pathway, was positively correlated with HIF-1α expression in 176 endometrial cancer patients extracted from the TCGA database. Hypoxia induced caspase-dependent MST2 cleavage. In addition, a MST2 inhibitor suppressed HIF-1α-mediated reporter activity. These results suggest HIF-1α and the Hippo signaling pathway are involved in endometrial cancer.

The tumor suppressor role of salvador family WW domain-containing protein 1 (SAV1): one of the key pieces of the tumor puzzle

PURPOSE

In the complex tumor scenario, understanding the function of proteins with protumor or antitumor roles is essential to support advances in the cancer clinical area. Among them, the salvador family WW domain-containing protein 1 (SAV1) is highlighted. This protein plays a fundamental role in the tumor suppressor face of the Hippo pathway, which are responsible for controlling cell proliferation, organ size, development and tissue homeostasis. However, the functional dysregulation of this pathway may contribute to tumorigenesis and tumor progression. As SAV1 is a tumor suppressor scaffold protein, we explored the functions performed by SAV1 with its partners, the regulation of its expression, and its antitumor role in various types of cancer.

METHODS

We selected and analyzed 80 original articles and reviews from Pubmed that focuses on the study of SAV1 in cancer.

RESULTS

SAV1 interacts with several proteins, has different functions and acts as tumor suppressor by other mechanisms besides Hippo pathway. SAV1 expression regulation seems to occur by microRNAs and rarely by mutation or promoter methylation. It is downregulated in different types of cancer, which leads to cancer promotion and progression and is associated with poor prognosis. In vivo models have shown that the loss of SAV1 contributes to tumorigenesis.

CONCLUSION

SAV1 plays a relevant role as tumor suppressor in several types of cancer, highlighting SAV1 and the Hippo pathway's importance to cancer. Thus, encouraging further studies to include the SAV1 as a molecular key piece in cancer biology and in clinical approaches to cancer.

STK3 Suppresses Ovarian Cancer Progression by Activating NF-κB Signaling to Recruit CD8+ T-Cells

Serine/threonine protein kinase-3 (STK3) is a critical molecule of the Hippo pathway but little is known about its biological functions in the ovarian cancer development. We demonstrated the roles of STK3 in ovarian cancer. Existing databases were used to study the expression profile of STK3. STK3 was significantly downregulated in OC patients, and the low STK3 expression was correlated with a poor prognosis. In vitro cell proliferation, apoptosis, and migration assays, and in vivo subcutaneous xenograft tumor models were used to determine the roles of STK3. The overexpression of STK3 significantly inhibited cell proliferation, apoptosis, and migration of ovarian cancer cells in vitro and tumor growth in vivo. Bisulfite sequencing PCR analysis was performed to validate the methylation of STK3 in ovarian cancer. RNA sequencing and gene set enrichment analysis (GSEA) were used to compare the transcriptome changes in the STK3 overexpression ovarian cancer and control cells. The signaling pathway was analyzed by western blotting. STK3 promoted the migration of CD8⁺ T-cells by activating nuclear transcription factor κB (NF-κB) signaling. STK3 is a potential predictor of OC. It plays an important role in suppressing tumor growth of ovarian cancer and in chemotaxis of CD8⁺ T-cells.

MST2 silencing induces apoptosis and inhibits tumor growth for estrogen receptor alpha-positive MCF-7 breast cancer

Mammalian sterile 20-like kinase 1/2 (MST1/2) plays an important role in cell growth and apoptosis and functions as a tumor suppressor. Previously, we showed that MST2 overexpression activates Estrogen receptor alpha (ERα) in human breast cancer MCF-7 cells in the absence of a ligand. Here, we examined the role of MST2 in the growth of ER-positive MCF-7 cells. Cell cycle, apoptosis, and mammosphere formation assay method were implemented to detect the biological effects of MST2 ablation on the growth of MCF-7 cells in vitro. The effect of MST2-siRNA on MCF-7 cells tumor growth in vivo was studied in tumor-bearing mouse model. Kaplan-Meier plotter analysis was used to determine the effect of MST2 on overall survival in breast cancer patients. MST2 overexpression increased cell viability marginally. The ablation of MST2 using siRNA dramatically suppressed the viability of the MCF-7 cells, but not ER-negative MDA-MB-231 breast cancer cells. Furthermore, MST2 knockdown increased caspase-dependent apoptosis and led to decreased mammosphere formation. Treatment of MCF-7 tumor-bearing mice with MST2 siRNA significantly inhibited tumor growth. The tumor weight was reduced further when tamoxifen was added. Patients with ER-positive breast cancer with low MST2 expression had better overall survival than did those with high MST2 expression in Kaplan-Meier survival analyses using public datasets. Our results provide new insight into the role of MST2, a key component of the Hippo signaling pathway, in mediating breast cancer progression.

Hypoxia induced phosphorylation of estrogen receptor at serine 118 in the absence of ligand

The estrogen receptor (ER) plays an important role in breast cancer development and progression. Hypoxia modulates the level of ERα expression and induces ligand-independent transcriptional activation of ERα, which is closely related with the biology of breast carcinomas. Since phosphorylation itself affects the transcriptional activity and stabilization of ERα, we examined changes in ERα phosphorylation under hypoxic conditions. Hypoxia induced phosphorylation of ERα at serine residue 118 (S118) in the absence of estrogen through the mitogen-activated protein kinase (MAPK)/ERK1/2 pathway. Cell proliferation was significantly decreased under normoxia or hypoxia when ERα harboring the S118A mutation was overexpressed. Our previous studies showed that ER degradation is the most prominent phenomenon under hypoxia. E2-induced ER protein downregulation is dependent on phosphorylation of S118. However, hypoxia-induced ERα degradation did not involve S118 phosphorylation. Our study implies the existence of a differential mechanism between E2 and hypoxia-mediated ERα protein degradation. Understanding the mechanistic behavior of ER under hypoxia will likely facilitate understanding of endocrine therapy resistance and development of treatment strategies for breast cancer.

MST1/MST2 Protein Kinases: Regulation and Physiologic Roles

The MST1 and MST2 protein kinases comprise the GCK-II subfamily of protein kinases. In addition to their amino-terminal kinase catalytic domain, related to that of the Saccharomyces cerevisiae protein kinase Ste20, their most characteristic feature is the presence near the carboxy terminus of a unique helical structure called a SARAH domain; this segment allows MST1/MST2 to homodimerize and to heterodimerize with the other polypeptides that contain SARAH domains, the noncatalytic polypeptides RASSF1-6 and Sav1/WW45. Early studies emphasized the potent ability of MST1/MST2 to induce apoptosis upon being overexpressed, as well as the conversion of the endogenous MST1/MST2 polypeptides to constitutively active, caspase-cleaved catalytic fragments during apoptosis initiated by any stimulus. Later, the cleaved, constitutively active form of MST1 was identified in nonapoptotic, quiescent adult hepatocytes as well as in cells undergoing terminal differentiation, where its presence is necessary to maintain those cellular states. The physiologic regulation of full length MST1/MST2 is controlled by the availability of its noncatalytic SARAH domain partners. Interaction with Sav1/WW45 recruits MST1/MST2 into a tumor suppressor pathway, wherein it phosphorylates and activates the Sav1-bound protein kinases Lats1/Lats2, potent inhibitors of the Yap1 and TAZ oncogenic transcriptional regulators. A constitutive interaction with the Rap1-GTP binding protein RASSF5B (Nore1B/RAPL) in T cells recruits MST1 (especially) and MST2 as an effector of Rap1's control of T cell adhesion and migration, a program crucial to immune surveillance and response; loss of function mutation in human MST1 results in profound immunodeficiency. MST1 and MST2 are also regulated by other protein kinases, positively by TAO1 and negatively by Par1, SIK2/3, Akt, and cRaf1. The growing list of candidate MST1/MST2 substrates suggests that the full range of MST1/MST2's physiologic programs and contributions to pathophysiology remains to be elucidated.

Activation of Estrogen Receptor by Bavachin from Psoralea corylifolia

In this study, we examined the estrogenic activity of bavachin, a component of Psoralea corylifolia that has been used as a traditional medicine in Asia. Bavachin was purified from ethanolic extract of Psoralea corylifolia and characterized its estrogenic activity by ligand binding, reporter gene activation, and endogenous estrogen receptor (ER) target gene regulation. Bavachin showed ER ligand binding activity in competitive displacement of [(3)H] E2 from recombinant ER. The estrogenic activity of bavachin was characterized in a transient transfection system using ERα or ERβ and estrogen-responsive luciferase plasmids in CV-1 cells with an EC50 of 320 nM and 680 nM, respectively. Bavachin increased the mRNA levels of estrogen-responsive genes such as pS2 and PR, and decreased the protein level of ERα by proteasomal pathway. However, bavachin failed to activate the androgen receptor in CV-1 cells transiently transfected with the corresponding receptor and hormone responsive reporter plasmid. These data indicate that bavachin acts as a weak phytoestrogen by binding and activating the ER.