Identification of nuclear localization sequence of CXCR4 in renal cell carcinoma by constructing expression plasmids of different deletants

Understanding the impact of nuclear-localized GPCRs on cellular signalling

G protein-coupled receptors (GPCRs) have historically been associated with signalling events driven from the plasma membrane. More recently, signalling from endosomes has been recognized as a feature of internalizing receptors. However, there was little consideration given to the notion that GPCRs can be targeted to distinct subcellular locations that did not involve an initial trafficking to the cell surface. Here, we focus on the evidence for and the potential impact of GPCR signalling specifically initiated from the nuclear membrane. We also discuss the possibilities for selectively targeting this and other internal pools of receptors as novel venues for drug discovery.

CXCR4 Expression as a Prognostic Biomarker in Soft Tissue Sarcomas

Poor long-term survival in localized high-risk soft tissue sarcomas (STSs) of the extremities and trunk highlights the need to identify new prognostic factors. CXCR4 is a chemokine receptor involved in tumor progression, angiogenesis, and metastasis. The aim of this study was to evaluate the association between CXCR4 expression in tumor tissue and survival in STSs patients treated with neoadjuvant therapy. CXCR4 expression was retrospectively determined by immunohistochemical analysis in serial specimens including initial biopsies, tumors post-neoadjuvant treatment, and tumors after relapse. We found that a positive cytoplasmatic expression of CXCR4 in tumors after neoadjuvant treatment was a predictor of poor recurrence-free survival (RFS) (p = 0.003) and overall survival (p = 0.019) in synovial sarcomas. We also found that positive nuclear CXCR4 expression in the initial biopsies was associated with poor RFS (p = 0.022) in undifferentiated pleomorphic sarcomas. In conclusion, our study adds to the evidence that CXCR4 expression in tumor tissue is a promising prognostic factor for STSs.

The CXC Chemokine Receptors in Four-Eyed Sleeper (Bostrychus sinensis) and Their Involvement in Responding to Skin Injury

CXC Chemokine signaling plays an important role in wound healing. The four-eyed sleeper (Bostrychus sinensis) is a commercially important marine fish, which is prone to suffer skin ulceration at high temperature seasons, leading to mass mortality of fish in aquaculture farms. The genetic background related to skin ulceration and wound healing has remained unknown in this fish. Herein, we identified 10 differentially expressed Bostrychus sinensis CXC chemokine receptors (BsCXCRs) in skin ulcerated fish by de novo transcriptome sequencing. The transcripts of these BsCXCRs were classified in seven types, including BsCXCR1a/1b, BsCXCR2, BsCXCR3a1/3a2, BsCXCR4a/4b, and BsCXCR5-7, and BsCXCR6 was the first CXCR6 homologue experimentally identified in teleost fish. These BsCXCRs were further characterized in gene and protein structures, as well as phylogenetics, and the results revealed that BsCXCRs have expanded to divergent homologues. Our results showed that, in healthy fish, the BsCXCR transcripts was mainly distributed in the muscle and immune related organs, and that BsCXCR1a/1b proteins located in the cytomembrane, BsCXCR4a/4b/5/6 in the cytomembrane and perinuclear region, and BsCXCR3a1/3a2/7 in the cytomembrane, perinuclear region, and nuclear membrane, respectively. In skin injured fish, the transcripts of all BsCXCRs were transiently increased within one hour after injury, suggesting the involvement of BsCXCRs into the early inflammatory response to skin injury in the four-eyed sleeper. These results are valuable for understanding the evolutionary events of fish CXCR genes and provide insights into the roles of CXCR family in fish skin injury.

NMMHC-IIA-dependent nuclear location of CXCR4 promotes migration and invasion in renal cell carcinoma

The chemokine receptor cysteine (C)-X-C receptor (CXCR4) is a G-protein-coupled receptor that exerts a vital role in distant metastasis of renal cell carcinoma (RCC). Emerging evidence demonstrates that CXCR4 as the cytomembrane receptor translocated into the nucleus to facilitate cell migration and, therefore, determine the prognosis of several types of malignancies. However, the biological mechanism of nuclear location of CXCR4 remains unclear. In the present study, we confirmed the significant implications of the putative nuclear localization sequence (NLS) '146RPRK149̓ on CXCR4 subcellular localization and metastatic potential by point-mutation assay in RCC cell lines. Importantly, mass spectrum followed by immunoprecipitation identified non-muscle myosin heavy chain-IIA (NMMHC-IIA) as the CXCR4-interacting protein. Furthermore, pharmaceutical inhibition of NMMHC-IIA by blebbistatin dampened the nuclear translocation of CXCR4 as well as the metastatic capacity of RCC cells. In conclusion, the present study may drive the comprehensive progress toward elucidating the mechanism responsible for CXCR4 nuclear function and metastasis in tumors.

Intracellular trafficking and endocytosis of CXCR4 in fetal mesenchymal stem/stromal cells

Background

Fetal mesenchymal stem/stromal cells (MSC) represent a developmentally-advantageous cell type with translational potential.

To enhance adult MSC migration, studies have focussed on the role of the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12), but more recent work implicates an intricate system of CXCR4 receptor dimerization, intracellular localization, multiple ligands, splice variants and nuclear accumulation. We investigated the intracellular localization of CXCR4 in fetal bone marrow-derived MSC and role of intracellular trafficking in CXCR4 surface expression and function.

Results

We found that up to 4% of human fetal MSC have detectable surface-localized CXCR4. In the majority of cells, CXCR4 is located not at the cell surface, as would be required for ‘sensing’ migratory cues, but intracellularly. CXCR4 was identified in early endosomes, recycling endosomes, and lysosomes, indicating only a small percentage of CXCR4 travelling to the plasma membrane. Notably CXCR4 was also found in and around the nucleus, as detected with an anti-CXCR4 antibody directed specifically against CXCR4 isoform 2 differing only in N-terminal sequence. After demonstrating that endocytosis of CXCR4 is largely independent of endogenously-produced SDF-1, we next applied the cytoskeletal inhibitors blebbistatin and dynasore to inhibit endocytotic recycling. These increased the number of cells expressing surface CXCR4 by 10 and 5 fold respectively, and enhanced the number of cells migrating to SDF1 in vitro (up to 2.6 fold). These molecules had a transient effect on cell morphology and adhesion, which abated after the removal of the inhibitors, and did not alter functional stem cell properties.

Conclusions

We conclude that constitutive endocytosis is implicated in the regulation of CXCR4 membrane expression, and suggest a novel pharmacological strategy to enhance migration of systemically-transplanted cells.

Cysteine (C)-x-C receptor 4 undergoes transportin 1-dependent nuclear localization and remains functional at the nucleus of metastatic prostate cancer cells

The G-protein coupled receptor (GPCR), Cysteine (C)-X-C Receptor 4 (CXCR4), plays an important role in prostate cancer metastasis. CXCR4 is generally regarded as a plasma membrane receptor where it transmits signals that support transformation, progression and eventual metastasis. Due to the central role of CXCR4 in tumorigenesis, therapeutics approaches such as antagonist and monoclonal antibodies have focused on receptors that exist on the plasma membrane. An emerging concept for G-protein coupled receptors is that they may localize to and associate with the nucleus where they retain function and mediate nuclear signaling. Herein, we demonstrate that CXCR4 associated with the nucleus of malignant prostate cancer tissues. Likewise, expression of CXCR4 was detected in nuclear fractions among several prostate cancer cell lines, compared to normal prostate epithelial cells. Our studies identified a nuclear pool of CXCR4 and we defined a nuclear transport pathway for CXCR4. We reveal a putative nuclear localization sequence (NLS), ‘RPRK’, within CXCR4 that contributed to nuclear localization. Additionally, nuclear CXCR4 interacted with Transportinβ1 and Transportinβ1-binding to CXCR4 promoted its nuclear translocation. Importantly, G_αi immunoprecipitation and calcium mobilization studies indicated that nuclear CXCR4 was functional and participated in G-protein signaling, revealing that the nuclear pool of CXCR4 retained function. Given the suggestion that functional, nuclear CXCR4 may be a mechanism underlying prostate cancer recurrence, increased metastatic ability and poorer prognosis after tumors have been treated with therapy that targets plasma membrane CXCR4, these studies addresses a novel mechanism of nuclear signaling for CXCR4, a novel mechanism of clinical targeting, and demonstrate an active nuclear pool that provides important new information to illuminate what has been primarily clinical reports of nuclear CXCR4.

Silencing of CXCR4 by RNA interference inhibits cell growth and metastasis in human renal cancer cells

Renal cell carcinoma (RCC) is the third most common genitourinary malignancy, accounting for 3% of cancer in adults. The mortality and morbidity of RCC is strongly associated with its high propensity to metastasize to specific organs. This may be attributed to the fact that the CXCR4 G protein-coupled receptor (GPCR) on RCC cells mediates chemoattraction toward stromal-derived factor 1 (SDF-1) secreted by target organs. RNA interference (RNAi), which has been proven to be a powerful tool for suppressing gene expression, may lead to novel strategies for treating RCC. Our previous experiments confirmed that RCC A-498 cells overexpressing CXCR4 are associated with increased invasiveness. In this study, we constructed recombinant CXCR4-RNAi plasmids and transfected them into A-498 cells in vitro. Reverse transcription polymerase chain reaction (RT-PCR) and western blotting revealed that CXCR4 was downregulated in transfected cells compared with control cells. Our results from MTT and transwell migration assays indicated that specific downregulation of CXCR4 inhibited cell growth, invasiveness and migration. Flow cytometric analysis indicated that silencing of CXCR4 in A-498 cells by RNA interference induced cell apoptosis in RCC in vitro. Thus, siRNA targeting of CXCR4 can effectively inhibit the growth and metastasis of RCC cells and may be a promising innovative anticancer therapy.

Effects of transplantation of adipose tissue-derived stem cells on prostate tumor

BACKGROUND

Obesity is a risk factor for prostate cancer development, but the underlying mechanism is unknown. The present study tested the hypothesis that stromal cells of the adipose tissue might be recruited by cancer cells to help tumor growth.

METHODS

PC3 prostate cancer cells were transplanted into the subcutaneous space of the right flank of athymic mice. One week later, adipose tissue-derived stromal or stem cells (ADSC) or phosphate-buffered saline (PBS, as control) was transplanted similarly to the left flank. Tumor size was monitored for the next 34 days; afterwards, the mice were sacrificed and their tumors harvested for histological examination. The ability of PC3 cells to attract ADSC was tested by migration assay. The involvement of the CXCL12/CXCR4 axis was tested by migration assay in the presence of a specific inhibitor AMD3100.

RESULTS

Throughout the entire course, the average size of PC3 tumors in ADSC-treated mice was larger than in PBS-treated mice. ADSC were identified inside the tumors of ADSC-treated mice; CXCR4 expression was also detected. Migration assay indicated the involvement of the CXCL12/CXCR4 axis in the migration of ADSC toward PC3 cells. Capillary density was twice as high in the tumors of ADSC-treated mice than in the tumors of PBS-treated mice. VEGF expression was similar but FGF2 expression was significantly higher in tumors of ADSC-treated mice than in the tumors of PBS-tread mice.

CONCLUSION

Prostate cancer cells recruited ADSC by the CXCL12/CXCR4 axis. ADSC helps tumor growth by increasing tumor vascularity, and which was mediated by FGF2.