Relationship Between Increased Expression of the Axl/Gas6 Signal Cascade and Prognosis of Patients with Upper Tract Urothelial Carcinoma

Prognostic value and immunological role of AXL gene in clear cell renal cell carcinoma associated with identifying LncRNA/RBP/AXL mRNA networks

Backgrounds

This article aimed to explore the prognostic and immunological roles of AXL gene in clear cell renal cell carcinoma (ccRCC) for overall survival (OS) and to identify the LncRNA/RBP/AXL mRNA networks.

Methods

AXL-related gene expression matrix and clinical data were obtained from The Cancer Genome Atlas (TCGA) dataset and AXL-related pathways were identified by gene set enrichment analysis (GSEA). We performed univariate/multivariate Cox regression analysis to evaluate independent prognostic factors and the relationships between AXL and immunity were also investigated.

Results

The outcomes of us indicated that the AXL mRNA expression was up-regulated in ccRCC samples and high expression of AXL was associated with worse OS in TCGA dataset (P < 0.01). Further external verification results from HPA, UALCAN, ICGC dataset, GSE6344, GSE14994, and qRT-PCR remained consistent (all P < 0.05). AXL was also identified as an independent prognostic factor for ccRCC by univariate/multivariate Cox regression analysis (both P < 0.05). A nomogram including AXL expression and clinicopathological factors was established by us and GSEA results found that elevated AXL expression was associated with the JAK-STAT, P53, WNT, VEGF and MAPK signaling pathways. In terms of immunity, AXL was dramatically linked to tumor microenvironment, immune cells, immune infiltration, immune checkpoint molecules and tumor mutational burden (TMB). As for its potential mechanisms, we also identified several LncRNA/RBP/AXL mRNA axes.

Conclusions

AXL was revealed to play prognostic and immunological roles in ccRCC and LncRNA/RBP/AXL mRNA axes were also identified by us for its potential mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02322-y.

A review on the role of GAS6 and GAS6-AS1 in the carcinogenesis

Growth arrest specific 6 (GAS6) encodes a protein that serves as a ligand for AXL receptor tyrosine kinase and stimulates cell proliferation. Notably, an antisense RNA, namely GAS6-AS1 is transcribed from chromosome 13q34, near GAS6 gene. In vitro functional experiments have demonstrated that GAS6-AS1 can promote proliferation, migration and invasive properties of transformed cells through enhancing entry into S-phase. Notably, mechanistic investigations have shown that GAS6-AS1 can regulate expression of GAS6 at the transcriptional or translational stages through constructing a RNA-RNA duplex, thus enhancing expression of AXL and inducing AXL signaling. Both GAS6 and its antisense transcript contribute in the pathogenesis of human malignancies. In the current review, we provide a summary of studies that appraised the role of these genes in the carcinogenesis.

Gas6 expression and Tyrosine kinase Axl Sky receptors: Their relation with tumor stage and grade in patients with bladder cancer

OBJECTIVES

It has been shown that the dysregulation of tyrosine kinase Axl receptor and its ligand growth arrest-specific gene (Gas6) are associated with poor prognosis in various types of tumors but there is not enough study about their importance in bladder cancer (BC). We evaluated the relation of Gas6 gene expression and tyrosine- kinase Axl and Sky (Tyro 3) receptors with tumor stage and grade in patients with BC.

MATERIAL AND METHODS

The study group consists of 55 patients whose transurethral resection of bladder (TUR-B) has been performed due to BC and the control group consists of 12 patients with normal bladder mucosa. In tissues mRNAs of Gas6, Axl, and Sky receptors were examined by quantitative (Real-Time) PCR (qPCR). Protein expression was measured by immunohistochemistry. Plasma Gas6 protein levels were compared with control group by ELISA method.

RESULTS

Patients with BC were grouped as Ta low (n=17), Ta high (n=5), T1 low (n=9), T1 high (n=8) and T2 (n=16) according to their TUR-B pathologies. The qPCR analysis showed that the expression of Gas6 gene and Axl receptor is higher in the tumor-positive group and the immune-histochemical showed that the bladder samples of the tumor-positive group stained significantly positive. When the patients are grouped according to the TUR-B pathologies, a statistical significant difference was observed among groups in the qPCR analysis ratios of Gas6 gene and Axl receptor by (p < 0.05) but no significance was found for Sky receptor (p > 0.05). When Gas6 protein levels in plasma samples were compared by ELISA method, a statistical significance was determined among groups (p = 0.001).

CONCLUSIONS

Our findings indicate that mRNAs of Gas6 and Axl receptor are closely related to tumor stage and grade in patients with BC. Further studies are needed for understanding the role of Gas6 and its receptors on the neoplastic transformation in terms of novel biomarkers and potential therapeutic targets.

The role of epithelial-mesenchymal transition-regulating transcription factors in anti-cancer drug resistance

The complex orchestration of gene expression that mediates the transition of epithelial cells into mesenchymal cells is implicated in cancer development and metastasis. As the primary regulator of the process, epithelial-mesenchymal transition-regulating transcription factors (EMT-TFs) play key roles in metastasis. They are also highlighted in recent preclinical studies on resistance to cancer therapy. This review describes the role of three main EMT-TFs, including Snail, Twist1, and zinc-finger E homeobox-binding 1 (ZEB1), relating to drug resistance and current possible approaches for future challenges targeting EMT-TFs.

Cabozantinib in Combination with Immunotherapy for Advanced Renal Cell Carcinoma and Urothelial Carcinoma: Rationale and Clinical Evidence

The treatment landscape for metastatic renal cell carcinoma (mRCC) and urothelial carcinoma (mUC) has evolved rapidly in recent years with the approval of several checkpoint inhibitors. Despite these advances, survival rates for metastatic disease remain poor, and additional strategies will be needed to improve the efficacy of checkpoint inhibitors. Combining anti-VEGF/VEGFR agents with checkpoint inhibitors has emerged as a potential strategy to advance the immunotherapy paradigm, because VEGF inhibitors have immunomodulatory potential. Cabozantinib is a tyrosine kinase inhibitor (TKI) whose targets include MET, AXL, and VEGFR2. Cabozantinib has a unique immunomodulatory profile and has demonstrated clinical efficacy as a monotherapy in mRCC and mUC, making it a potentially suitable partner for checkpoint inhibitor therapy. In this review, we summarize the current status of immunotherapy for mRCC and mUC and discuss the development of immunotherapy-TKI combinations, with a focus on cabozantinib. We discuss the rationale for such combinations based on our growing understanding of the tumor microenvironment, and we review in detail the preclinical and clinical studies supporting their use.

Overexpression of GAS6 Promotes Cell Proliferation and Invasion in Bladder Cancer by Activation of the PI3K/AKT Pathway

Background

Growth arrest-specific 6 (GAS6) is a secreted vitamin K-dependent protein abnormally expressed in various human tumor tissues and can activate the receptor Tyro3, Axl, and Mer to promote cancer cell proliferation and invasion. Until now, the role of GAS6 has been poorly understood in bladder cancer (BCa).

Materials and Methods

Using bioinformatics analysis, we screened genes significantly associated with overall survival in BCa. The association between GAS6 and survival was evaluated by tissue microarray and IHC staining. We investigated the effect of GAS6 on the development of BCa through in vitro and in vivo experiments.

Results

Here, we report that GAS6 is highly expressed in bladder cancer and is significantly associated with tumor grade, T stage, and worse prognosis. We found that GAS6 depletion inhibited proliferation, migration, and invasion of BCa cells. In addition, bioinformatics analysis revealed that GAS6 may be involved in the regulation of PI3K-AKT signaling pathway by binding to receptor TAM and has a significant positive correlation with PI3K family gene expression. Furthermore, Western blot experiments have shown that GAS6 might modulate the PI3K-AKT signaling to regulate proliferation and invasion of BCa cells. Treatment of BCa cells with SC79, an AKT activator, partially restored the effect of GAS6 silencing on cell proliferation and invasion.

Conclusion

The present study suggests that GAS6 may play a pivotal role in the development of BCa and may be a potential target for its treatment.

Rational Drug Design of Axl Tyrosine Kinase Type I Inhibitors as Promising Candidates Against Cancer

The high level of Axl tyrosine kinase expression in various cancer cell lines makes it an attractive target for the development of anti-cancer drugs. In this study, we carried out several sets of in silico screening for the ATP-competitive Axl kinase inhibitors based on different molecular docking protocols. The best drug-like candidates were identified, after parental structure modifications, by their highest affinity to the target protein. We found that our newly designed compound R5, a derivative of the R428 patented analog, is the most promising inhibitor of the Axl kinase according to the three molecular docking algorithms applied in the study. The molecular docking results are in agreement with the molecular dynamics simulations using the MM-PBSA/GBSA implicit solvation models, which confirm the high affinity of R5 toward the protein receptor. Additionally, the selectivity test against other kinases also reveals a high affinity of R5 toward ABL1 and Tyro3 kinases, emphasizing its promising potential for the treatment of malignant tumors.

Genomics in upper tract urothelial carcinoma

PURPOSE OF REVIEW

Upper tract urothelial carcinoma (UTUC) is a relatively rare and poorly investigated disease. The objective of this review was to discuss recent advances in genomics and their implication regarding prognosis and treatment.

RECENT FINDINGS

UTUC were compared with urothelial carcinoma of the bladder (UCB) at genomic and transcriptomic levels. Molecular studies focused on identifying new prognostic biomarkers that were often initially described in UCB and extrapolated to UTUC. Some of them could be interesting to improve the management of UTUC.

SUMMARY

Recent studies improved our understanding of UTUC as a distinct entity compared with UCB. Although UTUC shares many of the same genomic alterations with UCB, some key differences have been identified as oncogenic drivers of these cancers. This better comprehension of genomics could lead to new prognostic markers that may refine UTUC treatment.

Axl inhibitors as novel cancer therapeutic agents

Overexpression and activation of Axl receptor tyrosine kinase have been widely accepted to promote cell proliferation, chemotherapy resistance, invasion, and metastasis in several human cancers, such as lung, breast, and pancreatic cancers. Axl, a member of the TAM (Tyro3, Axl, Mer) family, and its inhibitors can specifically break the kinase signaling nodes, allowing advanced patients to regain drug sensitivity with improved therapeutic efficacy. Therefore, the research on Axl is promising and it is worthy of further investigations. In this review, we present an update on the Axl inhibitors and provide new insights into their latent application.

The prognostic role of Gas6/Axl axis in solid malignancies: a meta-analysis and literature review

Background

Axl is a receptor tyrosine kinase that is involved in many pathological conditions and carcinogenesis. Gas6 is the major ligand of Axl. Activation of Gas6/Axl pathway is essential for cancer development. However, its prognostic significance in solid tumors remains unclear. Therefore, we performed this meta-analysis to elucidate the prognostic impact of Axl.

Methods

Published studies on Axl or Gas6 expression and overall survival (OS) and/or disease-free survival (DFS) were searched from databases. The outcome measurement is hazard ratio (HR) for OS or DFS related to Axl/Gas6 expression. Meta-analysis was performed using RevMan. The pooled HR was calculated by fixed-/random-effect models.

Results

A total of 3,344 patients from 25 studies were included. The results of meta-analysis showed that Axl overexpression was correlated with shorter OS (HR: 2.03, p<0.0001) and DFS (HR: 1.85, p<0.0001). In subgroup analysis, Axl expression was significantly correlated with poor prognosis in hepatocellular, esophageal and lung cancer. Axl expression was associated with differentiation grade, TNM stage, lymph node and distant metastasis.

Conclusion

These results suggest that Axl overexpression is correlated with poor prognosis in solid tumors. This correlation varies among different types of cancers. More studies are needed to further investigate the prognostic value of Axl.

Protein S drives oral squamous cell carcinoma tumorigenicity through regulation of AXL

The TAM family of proto-oncogenic receptor protein tyrosine kinases, comprising of TYRO3, AXL, and MERTK, is implicated in many human cancers. Their activation leads to cancer cell proliferation, enhanced migration, invasion, and drug resistance; however how TAMs are activated in cancers is less understood. We previously showed that Protein S (PROS1) is a ligand of the TAM receptors. Here we identify PROS1 as a mediator of Oral Squamous Cell Carcinoma (OSCC) in proliferation, cell survival and migration. We demonstrate that excess PROS1 induces OSCC proliferation and migration. Conversely, blocking endogenous PROS1 expression using shRNA significantly inhibits cell proliferation and migration in culture. This inhibition was rescued by the addition of purified PROS1. Moreover, PROS1 knockdown reduced anchorage-independent growth in-vitro, reduced tumor xenograft growth in nude mice and altered their differentiation profile. Mechanistically, we identify the downregulation of AXL transcripts and protein following PROS1 knockdown. Re-introducing PROS1 rescues AXL expression both at the protein and transcriptional levels. The anti-proliferative effect of the AXL inhibitor R428 was significantly reduced following PROS1 inhibition, indicating the functional significance of PROS1-mediated regulation of AXL in OSCC. Taken together, we identify PROS1 as a driver of OSCC tumor growth and a modulator of AXL expression. Our results point to PROS1 as a potential novel anti-cancer therapeutic target.

Role of AXL in invasion and drug resistance of colon and breast cancer cells and its association with p53 alterations

AIM

To characterize AXL receptor tyrosine kinase (AXL) expression in relationship to tumor protein P53 (TP53 gene, p53 protein) and its role in tumor invasion and response to therapy.

METHODS

We used 14 cell lines, including 3 isogenic pairs carrying mutant/knockout p53, to gain insight into the relationship between AXL and TP53. These included HCT116, HCT116.p53 mutant, RKO, and RKO.p53-/- lines (all from colon cancers) as well as breast cancer cell lines MCF7 and 1001 (MCF7-p53 mutant clone). HeLa cell line was used as a positive control for epithelial to mesenchymal transition (EMT). AXL expression was determined by Western blotting using rabbit monoclonal antibody clone C89E7. AXL siRNA silencing was performed and followed by collagen invasion assay. Cell viability analysis using the sulforhodamine B assay and the invasion assay were performed after exposure to chemotherapeutic agents (doxorubicin for breast cancer cells; 5FU or irinotecan for colon cancer cells).

RESULTS

We showed that the introduction of p53 mutations or knockout increased expression levels of AXL in isogenic cells compared to the matching p53 wild-type parental cells. Overall, we found a trend for correlation between the potential EMT candidate AXL, p53 alterations, and EMT markers in colorectal and breast cancers. The expression of AXL in RKO cells, a rare colon cancer cell line with inactive Wnt signaling, suggests that the AXL oncogene might provide an alternative genetic pathway for colorectal carcinogenesis in the absence of Wnt signaling activation and TP53 mutation. AXL silencing in the TP53 mutant isogenic cell lines 1001, HCT116.p53 mutant and RKO.P53-/- was > 95% efficient and the silenced cells were less invasive compared to the parental TP53 wild-type cells. AXL silencing showed a subtle trend to restore colon cancer cell sensitivity to 5FU or irinotecan. Importantly, AXL expressing cells developed more invasive potential after exposure to chemotherapy compared to the AXL-silenced cells.

CONCLUSION

AXL is influenced by p53 status and could cause the emergence of aggressive clones after exposure to chemotherapy. These findings could have applications in cancer management.

AXL and MET receptor tyrosine kinases are essential for lung cancer metastasis

The AXL and MET receptors regulate key processes in tumor growth, metastasis, and drug resistance; thus, they have recently been implicated as promising therapeutic targets in various tumors. We investigated the metastatic potential and crosstalk between these receptors in non‑small cell lung cancer (NSCLC). We found that the treatment of NSCLC cells with hepatocyte growth factor (HGF) and growth arrest-specific 6 (Gas6), as ligands for MET and AXL, respectively, promoted their migration and invasion ability. However, treatment with inhibitors of each of these receptors significantly reduced the migratory and invasiveness of the cells, although their inhibitory rates varied according to the inhibition of each receptor. In addition, the suppression of each receptor by shRNA resulted in reduced migration and invasiveness. Notably, the suppression of AXL was more effective than the suppression of MET in the inhibition of migration and invasion. In accordance with in vitro results, when the cells were transferred via tail vein injection, AXL inhibition was more efficient in attenuating metastasis than MET inhibition. Clinically, AXL or MET expression is associated with a poor prognosis in primary tumors of NSCLC. In summary, AXL and MET can regulate tumor metastasis, but AXL was shown to be more potent than MET in lung metastasis. Thus, we conclude that AXL might be a suitable therapeutic target for the inhibition of lung metastasis.

The Receptor Tyrosine Kinase AXL in Cancer Progression

The AXL receptor tyrosine kinase (AXL) has emerged as a promising therapeutic target for cancer therapy. Recent studies have revealed a central role of AXL signaling in tumor proliferation, survival, stem cell phenotype, metastasis, and resistance to cancer therapy. Moreover, AXL is expressed within cellular components of the tumor microenvironment where AXL signaling contributes to the immunosuppressive and protumorigenic phenotypes. A variety of AXL inhibitors have been developed and are efficacious in preclinical studies. These agents offer new opportunities for therapeutic intervention in the prevention and treatment of advanced disease. Here we review the literature that has illuminated the cellular and molecular mechanisms by which AXL signaling promotes tumor progression and we will discuss the therapeutic potential of AXL inhibition for cancer therapy.

Gas6/Axl Axis Contributes to Chemoresistance and Metastasis in Breast Cancer through Akt/GSK-3β/β-catenin Signaling

Chemoresistance in breast cancer has been of great interest in past studies. However, the development of rational therapeutic strategies targeting chemoresistant cells is still a challenge in clinical oncology. By integrating data from global differences of gene expression and phospho-receptor tyrosine kinases between sensitive parental cells (MCF-7) and doxorubicin-resistant cells (MCF-7/ADR), we identified Axl as a potential target for chemoresistance and metastasis in multidrug resistant breast cancer cells. We analyzed Axl expression in 57 breast cancer cell lines and detected a dramatic increase in its expression level in mesenchymal breast cancer cell lines. Axl silencing suppressed invasive and metastatic potentials of chemoresistant breast cancer cells as well as increased elimination of cancer cells when combined with doxorubicin. Furthermore, in preclinical assays, an Axl inhibitor R428 showed increased cell death upon doxorubicin treatment. Additionally, using phospho-kinase array based proteomic analysis, we identified that Akt/GSK-3β/β-catenin cascade was responsible for Axl-induced cell invasion. Nuclear translocation of β-catenin then induced transcriptional upregulation of ZEB1, which in turn regulated DNA damage repair and doxorubicin-resistance in breast cancer cells. Most importantly, Axl was correlated with its downstream targets in tumor samples and was associated with poor prognosis in breast cancer patients. These results demonstrate that Gas6/Axl axis confers aggressiveness in breast cancer and may represent a therapeutic target for chemoresistance and metastasis.