Ras Suppressor-1 (RSU-1) in Cancer Cell Metastasis: Friend or Foe?

Comprehensive analysis of cell-extracellular matrix protein Ras suppressor-1 in function and prognosis of gastrointestinal cancers

BACKGROUND

Ras suppressor 1 (RSU1), a highly conserved protein, plays an important role in actin cytoskeleton remodeling and cell-extracellular matrix adhesion. Aberration of RSU1 activity can cause changes in cell adhesion and migration, thereby enhancing tumor proliferation and metastasis. However, the correlation between RSU1 and gastrointestinal cancers (GICs), as well as its prognostic role related to tumor-infiltrating immune cells (TIICs) remains unclear.

AIM

To shows RSU1 plays a potential promoting role in facilitating tumor immune escape in GIC.

METHODS

Differential expression of RSU1 in different tumors and their corresponding normal tissues was evaluated by exploring the Gene Expression Profiling Interactive Analysis (GEPIA) dataset. The correlation between RSU1 expression and prognosis of GIC cancer patients was evaluated by Kaplan-Meier plotter. Then, RSU1-correlated genes were screened and functionally characterized via enrichment analysis. The correlation between RSU1 and TIICs was further characterized using the Tumor Immune Estimation Resource (TIMER). In addition, the correlation between RSU1 and immune cell surface molecules was also analyzed by TIMER.

RESULTS

High RSU1 expression was associated with poor overall survival of gastric cancer patients, exhibiting a hazard ratio (HR) = 1.36, first progression HR = 1.53, and post progression survival HR = 1.6. Specifically, high RSU1 Levels were associated with prognosis of gastric cancer in females, T4 and N3 stages, and Her-2-negative subtypes. Regarding immune-infiltrating cells, RSU1 expression level was positively correlated with infiltration of CD4+ T cells, macrophages, neutrophils, and dendritic cells (DCs) in colorectal adenocarcinoma and stomach adenocarcinoma. RSU1 expression was also predicted to be strongly correlated with immune marker sets in M2 macrophage, DCs and T cell exhaustion in GICs.

CONCLUSION

In gastrointestinal cancers, RSU1 is increased in tumor tissues, and predicts poor survival of patients. Increased RSU1 may be involved in promoting macrophage polarization, DC infiltration, and T cell exhaustion, inducing tumor immune escape and the development of tumors in GICs. We suggest that RSU1 is a promising prognostic biomarker reflecting immune infiltration level of GICs, as well as a potential therapeutic target for precision treatment through improving the immune response.

Ras suppressor-1 (RSU1) exerts a tumor suppressive role with prognostic significance in lung adenocarcinoma

Ras suppressor-1 (RSU1), originally described as a suppressor of Ras oncogenic transformation, localizes to focal adhesions interacting with the ILK-PINCH-PARVIN (IPP) complex that exerts a well-established oncogenic role in cancer. However, RSU1 implication in lung cancer is currently unknown. Our study aims to address the role of RSU1 in lung adenocarcinoma (LUADC). We here show that RSU1 protein expression by immunohistochemistry is downregulated in LUADC human tissue samples and represents a significant prognostic indicator. In silico analysis of gene chip and RNA seq data validated our findings. Depletion of RSU1 by siRNA in lung cancer cells promotes anchorage-independent cell growth, cell motility and epithelial to mesenchymal transition (EMT). Silencing of RSU1 also alters IPP complex expression in lung cancer cells. The p29 RSU1 truncated isoform is detected in lung cancer cells, and its expression is downregulated upon RSU1 silencing, whereas it is overexpressed upon ILK overexpression. These findings suggest that RSU1 exerts a tumor suppressive role with prognostic significance in LUADC.

Complex structures of Rsu1 and PINCH1 reveal a regulatory mechanism of the ILK/PINCH/Parvin complex for F-actin dynamics

Communications between actin filaments and integrin-mediated focal adhesion (FA) are crucial for cell adhesion and migration. As a core platform to organize FA proteins, the tripartite ILK/PINCH/Parvin (IPP) complex interacts with actin filaments to regulate the cytoskeleton-FA crosstalk. Rsu1, a Ras suppressor, is enriched in FA through PINCH1 and plays important roles in regulating F-actin structures. Here, we solved crystal structures of the Rsu1/PINCH1 complex, in which the leucine-rich-repeats of Rsu1 form a solenoid structure to tightly associate with the C-terminal region of PINCH1. Further structural analysis uncovered that the interaction between Rsu1 and PINCH1 blocks the IPP-mediated F-actin bundling by disrupting the binding of PINCH1 to actin. Consistently, overexpressing Rsu1 in HeLa cells impairs stress fiber formation and cell spreading. Together, our findings demonstrated that Rsu1 is critical for tuning the communication between F-actin and FA by interacting with the IPP complex and negatively modulating the F-actin bundling.

Probing single-cell metabolism reveals prognostic value of highly metabolically active circulating stromal cells in prostate cancer

Despite their important role in metastatic disease, no general method to detect circulating stromal cells (CStCs) exists. Here, we present the Metabolic Assay-Chip (MA-Chip) as a label-free, droplet-based microfluidic approach allowing single-cell extracellular pH measurement for the detection and isolation of highly metabolically active cells (hm-cells) from the tumor microenvironment. Single-cell mRNA-sequencing analysis of the hm-cells from metastatic prostate cancer patients revealed that approximately 10% were canonical EpCAM⁺ hm-CTCs, 3% were EpCAM^- hm-CTCs with up-regulation of prostate-related genes, and 87% were hm-CStCs with profiles characteristic for cancer-associated fibroblasts, mesenchymal stem cells, and endothelial cells. Kaplan-Meier analysis shows that metastatic prostate cancer patients with more than five hm-cells have a significantly poorer survival probability than those with zero to five hm-cells. Thus, prevalence of hm-cells is a prognosticator of poor outcome in prostate cancer, and a potentially predictive and therapy response biomarker for agents cotargeting stromal components and preventing epithelial-to-mesenchymal transition.

Circular RNA circEXOC6B Inhibits the Progression of Ovarian Cancer by Sponging miR-421 and Regulating RUS1 Expression

Background

Evidence has been shown that circular RNAs (circRNAs) play a vital role during the development of ovarian cancer. However, the mechanism by which circEXOC6B regulates tumorigenesis of ovarian cancer remains unknown. Thus, this study aimed to investigate the role of circEXOC6B during the progression of ovarian cancer.

Materials and Methods

The dual-luciferase reporter system assay was used to determine the interaction between circEXOC6B, miR-421 and RUS1 in ovarian cancer, respectively. CCK8 and colony formatting were used to evaluate cell proliferation. Meanwhile, the expressions of RSU1, PINCH1 and ILK in SKOV3 cells were detected with Western blot.

Results

Downregulation of circEXOC6B markedly promoted the proliferation and invasion in A2780 cells. In contrast, upregulation of circEXOC6B significantly inhibited the proliferation and invasion in SKOV3 cells. Moreover, overexpression of circEXOC6B obviously induced the apoptosis of SKOV3 cells. Furthermore, luciferase reporter assay identified that miR-421 was the potential miRNA binding of circEXOC6B, and RUS1 was the potential binding target of miR-421. Mechanism analysis indicated that upregulation of circEXOC6B increased the level of RUS1 by acting as a competitive "sponge" of miR-421.

Conclusion

In this study, we found that circEXOC6B suppressed the growth of ovarian cancer cells through upregulating RSU1 partially via sponging miR-421. Therefore, circEXOC6B might be a potential target for the treatment of ovarian cancer.

Integrin-linked kinase (ILK) regulates KRAS, IPP complex and Ras suppressor-1 (RSU1) promoting lung adenocarcinoma progression and poor survival

Integrin-linked kinase (ILK) forms a heterotrimeric protein complex with PINCH and PARVIN (IPP) in Focal Adhesions (FAs) that acts as a signaling platform between the cell and its microenvironment regulating important cancer-related functions. We aimed to elucidate the role of ILK in lung adenocarcinoma (LUADC) focusing on a possible link with KRAS oncogene. We used immunohistochemistry on human tissue samples and KRAS-driven LUADC in mice, analysis of large scale publicly available RNA sequencing data, ILK overexpression and pharmacological inhibition as well as knockdown of KRAS in lung cancer cells. ILK, PINCH1 and PARVB (IPP) proteins are overexpressed in human LUADC and KRAS-driven LUADC in mice representing poor prognostic indicators. Genes implicated in ILK signaling are significantly enriched in KRAS-driven LUADC. Silencing of KRAS, as well as, overexpression and pharmacological inhibition of ILK in lung cancer cells provide evidence of a two-way association between ILK and KRAS. Upregulation of PINCH, PARVB and Ras suppressor-1 (RSU1) expression was demonstrated in ILK overexpressing lung cancer cells in addition to a significant positive correlation between these factors in tissue samples, while KRAS silencing downregulates IPP and RSU1. Pharmacological inhibition of ILK in KRAS mutant lung cancer cells suppresses cell growth, migration, EMT and increases sensitivity to platinum-based chemotherapy. ILK promotes an aggressive lung cancer phenotype with prognostic and therapeutic value through functions that involve KRAS, IPP complex and RSU1, rendering ILK a promising biomarker and therapeutic target in lung adenocarcinoma.

Ras Suppressor-1 (RSU1) in Cancer Cell Metastasis: A Tale of a Tumor Suppressor

Cancer is a multifactorial disease responsible for millions of deaths worldwide. It has a strong genetic background, as mutations in oncogenes or tumor suppressor genes contribute to the initiation of cancer development. Integrin signaling as well as the signaling pathway of Ras oncogene, have been long implicated both in carcinogenesis and disease progression. Moreover, they have been involved in the promotion of metastasis, which accounts for the majority of cancer-related deaths. Ras Suppressor-1 (RSU1) was identified as a suppressor of Ras-induced transformation and was shown to localize to cell-extracellular matrix adhesions. Recent findings indicate that its expression is elevated in various cancer types, while its role in regulating metastasis-related cellular processes remains largely unknown. Interestingly, there is no in vivo work in the field to date, and thus, all relevant knowledge stems from in vitro studies. In this review, we summarize recent studies using breast, liver and brain cancer cell lines and highlight the role of RSU1 in regulating cancer cell invasion.

Coordinated Expression of Ras Suppressor 1 (RSU-1) and Growth Differentiation Factor 15 (GDF15) Affects Glioma Cell Invasion

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor due to its invasive phenotype. Ras suppressor 1 (RSU-1) is a cell-extracellular matrix adhesion protein and we recently found that it promotes cell invasion in aggressive cells and inhibits it in non-invasive. Growth differentiation factor-15 (GDF15) is known to be involved in actin cytoskeleton reorganization and metastasis. In this study, we used three brain cell lines (H4, SW1088 and A172) with increasing RSU-1 expression levels and invasive capacity and decreasing GDF15 levels to investigate the interplay between RSU-1 and GDF15 with regard to cell invasion. Four experimental approaches were used: (a) GDF15 treatment, (b) Rsu-1 silencing, (c) GDF15 silencing, and (d) combined GDF15 treatment and RSU-1 silencing. We found that the differential expression of RSU-1 and GDF15 in H4 and A172 cells leading to inhibition of cell invasion in H4 cells and promotion in A172 through respective changes in PINCH1, RhoA and MMP-13 expression. Interestingly SW1088, with intermediate RSU-1 and GDF15 expression, were not affected by any treatment. We conclude that there is a strong connection between RSU-1 and GDF15 in H4, SW1088 and A172 cells and the relative expression of these two proteins is fundamental in affecting their invasive fate.

Ras suppressor-1 (RSU-1) promotes cell invasion in aggressive glioma cells and inhibits it in non-aggressive cells through STAT6 phospho-regulation

Most gliomas are invasive tumors formed from glial cells and associated with high mortality rates. In this study, we characterized four glioma cell lines of varying degree of aggressiveness (H4, SW1088, A172 and U87-MG) in terms of morphology, cytoskeleton organization and stiffness, and evaluated their invasive potential by performing invasion, colony forming and spheroid invasion assays. Cells were divided into two distinct groups: aggressive cell lines (A172 and U87-MG) with more elongated, softer and highly invasive cells and less aggressive cells (H4 and SW088). Interestingly, we found that Ras Suppressor-1 (RSU-1), a cell-matrix adhesion protein involved in cancer cell invasion, was significantly upregulated in more aggressive glioma cells compared to less aggressive. Importantly, RSU-1 silencing had opposing effects on glioma cell invasion depending on their aggressiveness, inhibiting migration and invasion of aggressive cells and promoting those of less aggressive cells. Finally, we found that RSU-1 silencing in aggressive cells led to decreased Signal Transducer and Activator of Transcription6 (STAT6) phosphorylation and Matrix Metalloproteinase13 (MMP13) expression in contrast to less invasive cells. Our study demonstrates that RSU-1 promotes invasion of aggressive glioma cells and inhibits it in the non-aggressive cells, indicating that it could serve as a predictor of gliomas progression.

Inhibition of Breast Cancer Cell Invasion by Ras Suppressor-1 (RSU-1) Silencing Is Reversed by Growth Differentiation Factor-15 (GDF-15)

Extracellular matrix (ECM)-related adhesion proteins are important in metastasis. Ras suppressor-1 (RSU-1), a suppressor of Ras-transformation, is localized to cell–ECM adhesions where it interacts with the Particularly Interesting New Cysteine-Histidine rich protein (PINCH-1), being connected to Integrin Linked Kinase (ILK) and alpha-parvin (PARVA), a direct actin-binding protein. RSU-1 was also found upregulated in metastatic breast cancer (BC) samples and was recently demonstrated to have metastasis-promoting properties. In the present study, we transiently silenced RSU-1 in BC cells, MCF-7 and MDA-MB-231. We found that RSU-1 silencing leads to downregulation of Growth Differentiation Factor-15 (GDF-15), which has been associated with both actin cytoskeleton reorganization and metastasis. RSU-1 silencing also reduced the mRNA expression of PINCH-1 and cell division control protein-42 (Cdc42), while increasing that of ILK and Rac regardless of the presence of GDF-15. However, the downregulation of actin-modulating genes PARVA, RhoA, Rho associated kinase-1 (ROCK-1), and Fascin-1 following RSU-1 depletion was completely reversed by GDF-15 treatment in both cell lines. Moreover, complete rescue of the inhibitory effect of RSU-1 silencing on cell invasion was achieved by GDF-15 treatment, which also correlated with matrix metalloproteinase-2 expression. Finally, using a graph clustering approach, we corroborated our findings. This is the first study providing evidence of a functional association between RSU-1 and GDF-15 with regard to cancer cell invasion.