SPA-1 controls the invasion and metastasis of human prostate cancer

SIPA1 promotes epithelial-mesenchymal transition in colorectal cancer through STAT3 activation

Colorectal cancer (CRC) is the third leading cancer type worldwide and accounts for the second highest rate of cancer-related mortality. Liver metastasis significantly contributes to the mortality associated with CRC, but the fundamental mechanisms behind it remain unclear. Signal-induced proliferation-associated protein 1 (SIPA1), a GTPase activating protein, has been shown to promote metastasis in breast cancer. In this study, our objective was to explore the role of SIPA1 in regulating epithelial-mesenchymal transition (EMT) in CRC. The analysis of The Cancer Genome Atlas (TCGA) database revealed that the expression level of SIPA1 mRNA was notably upregulated and exhibited a positively correlated with EMT and STAT3 signaling pathways in CRC. Knockdown of SIPA1 impairs CRC cell proliferation and migration. Further studies on the reliance of SIPA1 on STAT3 signaling for EMT regulation have shown that SIPA1 stimulates the activation of STAT3, resulting in its nuclear translocation. The co-treatment of overexpressed SIPA1 with the STAT3 inhibitor STTITA has shown that SIPA1 regulates the expression of EMT-related markers through STAT3. Our study indicate that SIPA1 promotes CRC metastasis by activating the STAT3 signaling pathway, underscoring the potential of SIPA1 as a therapeutic target for metastatic CRC patients.

SIPA1 promotes angiogenesis by regulating VEGF secretion in Müller cells through STAT3 activation

Diabetic retinopathy (DR) is a prevalent complication of diabetes that can lead to vision loss. The chronic hyperglycemia associated with DR results in damage to the retinal microvasculature. Müller cells, as a kind of macroglia, play a crucial role in regulating the retinal vascular microenvironment. The objective of this study was to investigate the role of signal-induced proliferation-associated protein 1 (SIPA1) in regulating angiogenesis in Müller cells. Through proteomics, database analysis, endothelial cell function tests, and Western blot detection, we observed an up-regulation of SIPA1 expression in Müller cells upon high glucose stimulation. SIPA1 expression contributed to VEGF secretion in Müller cells and regulated the mobility of retinal vascular endothelial cells. Further investigation of the dependence of SIPA1 on VEGF secretion revealed that SIPA1 activated the phosphorylation STAT3, leading to its translocation into the nucleus. Overexpression of SIPA1 combined with the STAT3 inhibitor STATTIC demonstrated the regulation of SIPA1 in VEGF expression, dependent on STAT3 activation. These findings suggest that SIPA1 promotes the secretion of pro-angiogenic factors in Müller cells by activating the STAT3 signaling pathway, thereby highlighting SIPA1 as a potential therapeutic target for DR.

A novel transcription factor SIPA1: identification and verification in triple-negative breast cancer

Transcription factors (TFs) regulate the expression of genes responsible for cell growth, differentiation, and responses to environmental factors. In this study, we demonstrated that signal-induced proliferation-associated 1 (SIPA1), known as a Rap-GTPase-activating protein, bound DNA and served as a TF. Importin β1 was found to interact with SIPA1 upon fibronectin treatment. A TGAGTCAB motif was recognized and bound by DNA-binding region (DBR) of SIPA1, which was confirmed by electrophoretic mobility shift assay. SIPA1 regulated the transcription of multiple genes responsible for signal transduction, DNA synthesis, cell adhesion, cell migration, and so on. Transcription of fibronectin 1, which is crucial for cell junction and migration of triple-negative breast cancer (TNBC) cells, was regulated by SIPA1 in a DBR-dependent manner both in vivo and in vitro. Furthermore, single-cell transcriptome sequencing analysis of specimens from a metastatic TNBC patient revealed that SIPA1 was highly expressed in metastatic TNBC. Hence, this study demonstrated that SIPA1 served as a TF, promoting TNBC migration, invasion, and metastasis.

Extracellular Vesicles Derived from SIPA1high Breast Cancer Cells Enhance Macrophage Infiltration and Cancer Metastasis through Myosin-9

Simple Summary

The high expression of signal-induced proliferation-associated 1 (SIPA1) in breast cancer could aggravate cancer cell metastasis, but how the tumour microenvironment is involved in this incident is unknown. In this study, we investigated whether breast cancer cells with high SIPA1 expression recruited macrophages into the tumour microenvironment. We also found that extracellular vesicles (EVs) derived from MDA-MB-231 cells significantly enhanced macrophage migration, compared with that from SIPA1-knockdown MDA-MB-231 cells both in vitro and in vivo. In terms of the mechanism, SIPA1 in cancer cells modulated the key protein myosin-9 in EVs and promoted macrophage infiltration via EVs. We confirmed that either down-regulating SIPA1 expression or blocking myosin-9 by its inhibitor, blebbistatin, led to the suppression of macrophage infiltration. These findings contribute to a deep understanding of how SIPA1 regulates the tumour microenvironment in breast cancer to facilitate tumour metastasis and provide a basis for the development of therapeutics against breast cancer metastasis.

Abstract

Tumour cell metastasis can be genetically regulated by proteins contained in cancer cell-derived extracellular vesicles (EVs) released to the tumour microenvironment. Here, we found that the number of infiltrated macrophages was positively correlated with the expression of signal-induced proliferation-associated 1 (SIPA1) in invasive breast ductal carcinoma tissues and MDA-MB-231 xenograft tumours. EVs derived from MDA-MB-231 cells (231-EVs) significantly enhanced macrophage migration, compared with that from SIPA1-knockdown MDA-MB-231 cells (231/si-EVs) both in vitro and in vivo. We revealed that SIPA1 promoted the transcription of MYH9, which encodes myosin-9, and up-regulated the expression level of myosin-9 in breast cancer cells and their EVs. We also found that blocking myosin-9 by either down-regulating SIPA1 expression or blebbistatin treatment led to the suppression of macrophage infiltration. Survival analysis showed that breast cancer patients with high expression of SIPA1 and MYH9 molecules had worse relapse-free survival (p = 0.028). In summary, SIPA1^high breast cancer can enhance macrophage infiltration through EVs enriched with myosin-9, which might aggravate the malignancy of breast cancer.

Identification of metastasis-associated exoDEPs in colorectal cancer using label-free proteomics

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Exosomes play essential role in the metastasis of colorectal cancer from TME aspect.

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Finding out the prominent regulating exoDEPs by label-free proteomics in this research provided a lot of key information of CRC metastases.

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Metabolism, cytoskeleton-related pathways and immunosuppression are two key mechanisms by which exosomes regulate CRC malignant behavior.

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The discovery of the “all or none” exoDEPs was of great significance. The exoDEPs expressed only in SW620 cells can more clearly show their ability to promote the invasion and metastasis of CRC cells.

Exosomes are secreted nanovesicles consisting of biochemical molecules, including proteins, RNAs, lipids, and metabolites that play a prominent role in tumor progression. In this study, we performed a label-free proteomic analysis of exosomes from a pair of homologous human colorectal cancer cell line with different metastatic abilities. A total of 115 exoDEPs were identified, with 31 proteins upregulated and 84 proteins downregulated in SW620 exosome. We also detected 30 proteins expressed only in SW620 exosomes and 60 proteins expressed only in SW480 exosomes. Bioinformatics analysis enriched the components and pathways associated with the extracellular matrix, cytoskeleton-related pathways, and immune system changes of colorectal cancer (CRC). Cellular function experiments confirmed the role of SW620 exosomes in promoting the proliferation, migration, and invasion of SW480 cells. Further verifications were performed on six upregulated exoDEPs (FGFBP1, SIPA1, THBS1, TGFBI, COL6A1, and RPL10), three downregulated exoDEPs (SLC2A3, MYO1D, and RBP1), and three exoDEPs (SMOC2, GLG1, and CEMIP) expressed only in SW620 by WB and IHC. This study provides a complete and novel basis for exploring new drug targets to inhibit the invasion and metastasis of CRC.

SIPA1 Enhances Aerobic Glycolysis Through HIF-2α Pathway to Promote Breast Cancer Metastasis

Increased dependence on aerobic glycolysis is characteristic of most cancer cells, whereas the mechanism underlying the promotion of aerobic glycolysis in metastatic breast cancer cells under ambient oxygen has not been well understood. Here, we demonstrated that aberrant expression of signal-induced proliferation-associated 1 (SIPA1) enhanced aerobic glycolysis and altered the main source of ATP production from oxidative phosphorylation to glycolysis in breast cancer cells. We revealed that SIPA1 promoted the transcription of EPAS1, which is known as the gene encoding hypoxia-inducible factor-2α (HIF-2α) and up-regulated the expression of multiple glycolysis-related genes to increase aerobic glycolysis. We also found that blocking aerobic glycolysis by either knocking down SIPA1 expression or oxamate treatment led to the suppression of tumor metastasis of breast cancer cells both in vitro and in vivo. Taken together, aberrant expression of SIPA1 resulted in the alteration of glucose metabolism from oxidative phosphorylation to aerobic glycolysis even at ambient oxygen levels, which might aggravate the malignancy of breast cancer cells. The present findings indicate a potential target for the development of therapeutics against breast cancers with dysregulated SIPA1 expression.

SIPA1 boosts migration and proliferation, and blocks apoptosis of glioma by activating the phosphorylation of the FAK signaling pathway

Background

We aimed to analyze the regulatory effects of SIPA1 (signal-induced proliferation-associated protein 1) on glioma progression and the dominant signaling pathway.

Methods

Differential level of SIPA1 in glioma and normal tissues and cells was determined. Migratory, proliferative, apoptotic and cell cycle progression changes in A172 cells with overexpression or knockdown of SIPA1 were examined. Finally, protein levels of phosphorylated FAKs in A172 cells intervened by SIPA1, and the FAK inhibitor PF562271 were detected.

Results

SIPA1 was upregulated in glioma cases. Knock-down of SIPA1 reduced migratory and proliferative rates of glioma cells, increased apoptotic cell rate, and declined cell ratio in the S phase. The knockdown of SIPA1 also downregulated cell cycle proteins. In addition, SIPA1 upregulated phosphorylated FAKs in A172 cells and thus boosted malignant phenotypes of glioma.

Conclusions

SIPA1 is upregulated in glioma that boosts migratory and proliferative potentials of glioma cells by activating the phosphorylation of the FAK signaling pathway.

SIPA1 Is a Modulator of HGF/MET Induced Tumour Metastasis via the Regulation of Tight Junction-Based Cell to Cell Barrier Function

BACKGROUND

Lung cancer is the leading cause of cancer death. SIPA1 is a mitogen induced GTPase activating protein (GAP) and may hamper cell cycle progression. SIPA1 has been shown to be involved in MET signaling and may contribute to tight junction (TJ) function and cancer metastasis.

METHODS

Human lung tumour cohorts were analyzed. In vitro cell function assays were performed after knock down of SIPA1 in lung cancer cells with/without treatment. Quantitative polymerase chain reaction (qPCR) and western blotting were performed to analyze expression of HGF (hepatocyte growth factor), MET, and their downstream markers. Immunohistochemistry (IHC) and immunofluorescence (IFC) staining were performed.

RESULTS

Higher expression of SIPA1 in lung tumours was associated with a poorer prognosis. Knockdown of SIPA1 decreased invasiveness and proliferation of in vitro cell lines, and the SIPA1 knockdown cells demonstrated leaky barriers. Knockdown of SIPA1 decreased tight junction-based barrier function by downregulating MET at the protein but not the transcript level, through silencing of Grb2, SOCS, and PKCμ (Protein kinase Cµ), reducing the internalization and recycling of MET. Elevated levels of SIPA1 protein are correlated with receptor tyrosine kinases (RTKs), especially HGF/MET and TJs. The regulation of HGF on barrier function and invasion required the presence of SIPA1.

CONCLUSIONS

SIPA1 plays an essential role in lung tumourigenesis and metastasis. SIPA1 may be a diagnostic and prognostic predictive biomarker. SIPA1 may also be a potential therapeutic target for non-small cell lung cancer (NSCLC) patients with aberrant MET expression and drug resistance.

A novel nuclear localization region in SIPA1 determines protein nuclear distribution and epirubicin-sensitivity of breast cancer cells

Signal-induced proliferation-associated protein 1 (SIPA1) is highly expressed and mainly located in the nucleus in some breast cancer cell lines and clinical tumor tissues. Previous study revealed that nuclear localization of SIPA1 is functionally involved in breast cancer metastasis in the lymphatic gland. In the current study, we identified a non-typical region (140-179aa) of SIPA1 as a novel nuclear localization region (NLR) which is crucial for translocating the proteins into the nucleus in HEK293 cells and breast cancer cells. This region contained one basic amino acid, His160, and had no common features of typical nuclear localization signals. In addition, overexpressing SIPA1 without NLR could suppress breast cancer cell proliferation but could not promote cell migration in MCF7 cells. Furthermore, we found that a high expression of SIPA1 upregulated the expression of ABCB1, encoding multi-drug resistance protein MDR1, and promoted the resistance to epirubicin in breast cancer cells, while this effect was largely abolished in the cells with the expression of NLR-deleted SIPA1. This study overall, identified a nuclear localization-dependent region determining the nuclear distribution of SIPA1 and its regulation on epirubicin-sensitivity in breast cancer cells, which could be a potential drug target to facilitate the development of breast cancer chemotherapy.

SIPA1 enhances SMAD2/3 expression to maintain stem cell features in breast cancer cells

SIPA1, a GTPase activating protein that negatively regulates Ras-related protein (Rap), is a potential modulator of tumor metastasis and recurrence. In this study, we first showed that SIPA1 facilitated the stemness features of breast cancer cells, such as of tumorsphere formation capability and the expression of stemness marker CD44. In addition, SIPA1 promoted the expression of four stemness-associated transcription factors through increasing the expression of SMAD2 and SMAD3 in vitro and in vivo. The stemness features were abolished by blocking the phosphorylation of SMAD3 with its specific inhibitor SIS3. Furthermore, SIPA1 decreased the breast cancer cell sensitivity to chemotherapy drugs. This effect was, however, competitively reversed by blocking the SMAD3 phosphorylation by SIS3 treatment in breast cancer cells. Taken together, SIPA1 promotes and sustains the stemness of breast cancer cells and their resistance to chemotherapy by increasing the expression of SMAD2 and SMAD3, and blocking SMAD3 phosphorylation could suppress the cancer cell stemness and increase the sensitivity to chemotherapy in breast cancer cells expressing a high level of SIPA1.

Inhibition of microRNA-300 inhibits cell adhesion, migration, and invasion of prostate cancer cells by promoting the expression of DAB1

Prostate cancer (PC) is the most common malignancy in men. As per recent findings, microRNA-300 (miR-300) were found to be overexpressed in numerous types of cancers. In this study, we aimed to explore the effects of miR-300 on the adhesion, invasion, and migration of PC cells by targeting Disabled 1 (DAB1). Firstly, the regulatory role of miRNAs on DAB1 was predicted by screening PC-related differentially expressed genes (DEGs). Immunohistochemistry was applied to determine the positive protein expression of DAB1, after which the target relationship between miR-300 and DAB1 was examined. Loss-of-function and gain-of-function experiments were conducted to determine cell proliferation, adhesion, migration, invasion capability, and cell cycle of PC cells. Our data illustrated that DAB1 had a low expression, while miR-300 was expressed at a relatively high level in PC tissues. Moreover, our clinicopathological analysis revealed that there was a correlation between miR-300 and tumor, node, metastases stage, Gleason score, and lymph node metastasis of PC patients. DAB1 was also found to be poorly expressed in PC based on the findings from the microarray analysis. The results from dual-luciferase reporter gene assay corroborated that miR-300 interacts with DAB1. Importantly, overexpression of miR-300 and/or si-DAB1 resulted in the enhancement of RAC1, MMP2, MMP9, CyclinD1, and CyclinE expressions, whereas the expression of DAB1 and Rap was reduced in PC cells, thus suggesting that down-regulated miR-300 suppressed proliferation, adhesion, migration, and invasion of PC cells. Collectively, our results provided evidence that down-regulation of miR-300 inhibits the adhesion, migration, and invasion of PC cells.

The role of SIPA1 in the development of cancer and metastases (Review)

Cancer is a leading cause of mortality and the majority of deaths are due to metastases. Many molecules have been implicated in the development of metastases. Signal induced proliferation associated protein 1 (SIPA1), a mitogen-inducible gene, has been demonstrated to be involved in the metastasis of various solid tumours and may indicate a poor prognosis. Polymorphisms of SIPA1 can be associated with several different types of cancer and interactions between SIPA1 and binding molecules integrate a series of cellular functions, which may promote the development and metastasis of cancer. The mechanisms by which SIPA1 promotes the development and metastasis of cancer varies among tumour types. The present review describes the structure, function and regulation of SIPA1 and focuses on its role in cancer metastasis. Possibilities for future research and the clinical application of SIPA1 are also discussed.

5-Aza-2'-deoxycytidine advances the epithelial-mesenchymal transition of breast cancer cells by demethylating Sipa1 promoter-proximal elements

Human breast cancer cells exhibit considerable diversity in the methylation status of genomic DNA CpGs that regulate metastatic transcriptome networks. In this study, we identified human Sipa1 promoter-proximal elements that contained a CpG island and demonstrated that the methylation status of the CpG island was inversely correlated with SIPA1 protein expression in cancer cells. 5-Aza-2′-deoxycytidine (5-Aza-CdR), a DNA methyltransferase inhibitor, promoted the expression of Sipa1 in the MCF7 breast cancer cells with a low level of SIPA1 expression. On the contrary, in MDA-MB-231 breast cancer cells with high SIPA1 expression levels, hypermethylation of the CpG island negatively regulated the transcription of Sipa1. In addition, the epithelial–mesenchymal transition (EMT) was reversed after knocking down Sipa1 in MDA-MB-231 cells. However, the EMT was promoted in MCF7 cells with over-expression of SIPA1 or treated with 5-Aza-CdR. Taken together, hypomethylation of the CpG island in Sipa1 promoter-proximal elements could enhance SIPA1 expression in breast cancer cells, which could facilitate EMT of cancer cells, possibly increasing a risk of cancer cell metastasis in individuals treated with 5-Aza-CdR.

Summary: Hypomethylation by 5-Aza-CdR upregulates the SIPA1 expression and promotes epithelial–mesenchymal transition in breast cancer cells, possibly increasing the risk of cancer cell metastasis.

The prostate cancer risk variant rs55958994 regulates multiple gene expression through extreme long-range chromatin interaction to control tumor progression

Genome-wide association studies identified single-nucleotide polymorphism (SNP) rs55958994 as a significant variant associated with increased susceptibility to prostate cancer. However, the mechanisms by which this SNP mediates increased risk to cancer are still unknown. In this study, we show that this variant is located in an enhancer active in prostate cancer cells. Deletion of this enhancer from prostate tumor cells resulted in decreased tumor initiation, tumor growth, and invasive migration, as well as a loss of stem-like cells. Using a combination of capture chromosome conformation capture (Capture-C) and RNA sequencing, we identified genes on the same and different chromosomes as targets regulated by the enhancer. Furthermore, we show that expression of individual candidate target genes in an enhancer-deleted cell line rescued different aspects of tumorigenesis. Our data suggest that the rs55958994-associated enhancer affects prostate cancer progression by influencing expression of multiple genes via long-range chromatin interactions.

Sipa1 deficiency unleashes a host-immune mechanism eradicating chronic myelogenous leukemia-initiating cells

Chronic myelogenous leukemia (CML) caused by hematopoietic stem cells expressing the Bcr-Abl fusion gene may be controlled by Bcr-Abl tyrosine kinase inhibitors (TKIs). However, CML-initiating cells are resistant to TKIs and may persist as minimal residual disease. We demonstrate that mice deficient in Sipa1, which encodes Rap1 GTPase-activating protein, rarely develop CML upon transfer of primary hematopoietic progenitor cells (HPCs) expressing Bcr-Abl, which cause lethal CML disease in wild-type mice. Resistance requires both T cells and nonhematopoietic cells. Sipa1^−/− mesenchymal stroma cells (MSCs) show enhanced activation and directed migration to Bcr-Abl⁺ cells in tumor tissue and preferentially produce Cxcl9, which in turn recruits Sipa1^−/− memory T cells that have markedly augmented chemotactic activity. Thus, Sipa1 deficiency uncovers a host immune mechanism potentially capable of eradicating Bcr-Abl⁺ HPCs via coordinated interplay between MSCs and immune T cells, which may provide a clue for radical control of human CML.

Chronic myelogenous leukemia (CML)-initiating cells are resistant to kinase inhibitors. Here the authors show that deficiency of the Rap1 GTPase-activating protein Sipa1 in the tumor microenvironment releases an immune response that eradicates CML-initiating cells via interplay between stromal and T cells.

Roles of Rap1 signaling in tumor cell migration and invasion

Ras-associated protein-1 (Rap1), a small GTPase in the Ras-related protein family, is an important regulator of basic cellular functions (e.g., formation and control of cell adhesions and junctions), cellular migration, and polarization. Through its interaction with other proteins, Rap1 plays many roles during cell invasion and metastasis in different cancers. The basic function of Rap1 is straightforward; it acts as a switch during cellular signaling transduction and regulated by its binding to either guanosine triphosphate (GTP) or guanosine diphosphate (GDP). However, its remarkably diverse function is rendered by its interplay with a large number of distinct Rap guanine nucleotide exchange factors and Rap GTPase activating proteins. This review summarizes the mechanisms by which Rap1 signaling can regulate cell invasion and metastasis, focusing on its roles in integrin and cadherin regulation, Rho GTPase control, and matrix metalloproteinase expression.

[Identification analysis of eukaryotic expression plasmid Rap2a and its effect on the migration of lung cancer cells]

背景与目的

小G蛋白家族成员Rap2a可调控内皮素和细胞粘附从而影响细胞运动及细胞与基质间相互作用，但其在肿瘤发生发展中的作用仍属未知。克隆人Ras家族小G蛋白Rap2a的cDNA，构建其真核表达质粒并在肺癌细胞表达，初步探讨Rap2a在肺癌发生发展中的作用。

方法

Western blot检测Rap2a在肺癌细胞中的内源性表达。人骨肉瘤细胞株U2OS提取细胞总RNA，经逆转录聚合酶链式反应逆转录成cDNA，PCR扩增Rap2a基因，酶切后插入pcDNA3.1(+)构建真核表达质粒pcDNA3.1(+)-Rap2a，采用酶切及测序鉴定。重组质粒转染H1299和A549细胞，Western blot检测目的基因表达。Transwell小室迁移实验观察Rap2a对肺癌细胞迁移能力的影响。明胶酶谱实验检测Rap2a对细胞分泌基质金属蛋白酶（matrix metalloproteinase, MMP）2的影响。

结果

与正常细胞相比，肺癌细胞中Rap2a基础表达水平明显增高。双酶切及测序结果显示重组质粒pcDNA3.1(+)-Rap2a成功构建，Werstern blot检测到H1299和A549细胞有相应蛋白表达。迁移实验结果显示转染Rap2a基因后肿瘤细胞迁移能力明显增加。明胶酶谱实验结果显示Rap2a过表达后肺癌细胞分泌MMP2的量随之增加。

结论

人Rap2a真核表达质粒成功构建，Rap2a基因在肺癌细胞株成功表达并能促进肺癌细胞的迁移能力。

Suppression of SIPA-1 expression may reduce bladder cancer invasion and metastasis via the downregulation of E-cadherin and ZO-1

The aim of the present study was to investigate the capacity of signal-induced proliferation-associated protein 1 (SIPA-1) to regulate bladder cancer cell invasion and metastasis. BIU-87 and T24 cells were transfected with the SIPA gene and SIPA short hairpin (sh)RNA, respectively. Western blot analysis was conducted to analyze the expression levels of SIPA-1, Ras-related protein 1 (Rap1), Rap1 guanosine triphosphate (Rap1GTP), E-cadherin and zona occludens-1 (ZO-1). Cell motility and invasion were evaluated in vitro using wound and Transwell assays. Transfected cells were inoculated into the pelvic region of BALB/c nude mice, and the number of resulting tumors was recorded after 6 weeks. Western blot analysis revealed that expression levels of E-cadherin and ZO-1 were reduced in the cells with enhanced levels of SIPA-1. By contrast, the levels of E-cadherin and ZO-1 were elevated in the cells in which SIPA-1 was knocked down. In comparison with untransfected cells, the cells with reduced levels of SIPA-1 exhibited reduced wound closure and fewer cells crossed the chamber in the Transwell experiment, whereas the cells with enhanced levels of SIPA-1 exhibited increased migration and invasion In vivo, an increased tumor count was obtained in the mice with elevated levels of SIPA-1. Therefore, the results of the present study indicate that SIPA-1 is able to regulate bladder cancer cell metastasis and invasion by reducing the expression of E-cadherin and ZO-1.

Rap2a is a novel target gene of p53 and regulates cancer cell migration and invasion

The p53 transcription factor is a critical regulator of the cell cycle, DNA repair, and apoptosis. Recent evidences suggest that p53 may contribute to the regulation of cell invasion and migration. Rap2a, a member of the small GTPase superfamily, mediates diverse cellular events such as cell adhesion, migration and proliferation through various signaling pathways. In this study, we identify that Rap2a is a novel target of p53 and is induced upon DNA damage in a p53-dependent manner. Upon DNA damage, p53 directly binds to the promoter of Rap2a and activates its transcription. We show that Rap2a is significantly upregulated in many types of tumors. In addition, the ectopic expression of Rap2a enhances the migration and invasive ability of cancer cells and increases activities of matrix metalloproteinase MMP2 and MMP9. In contrast, the inactivation of Rap2a inhibits cell invasion and activities of MMP2 and MMP9. We also show that Rap2a regulates the phosphorylation level of Akt. Collectively, our results show that ectopic expression of Rap2a has a key role in enhancing migration, invasion and metastasis by upregulating p-Akt.

High SIPA-1 expression in proximal tubules of human kidneys under pathological conditions

Systemic lupus erythematosus (SLE) and clear cell renal cell carcinoma (CC-RCC) are serious disorders and usually fatal, and always accompanied with pathological changes in the kidney. Signal-induced proliferation-associated protein 1 (SIPA-1) is a Rap1GTPase activating protein (Rap1GAP) expressed in the normal distal and collecting tubules of the murine kidney. Lupus-like autoimmune disease and leukemia have been observed in SIPA-1 deficient mice, suggesting a pathological relevance of SIPA-1 to SLE and carcinoma in human being. The expression pattern of SIPA-1 is as yet undefined and the pathogenesis of these diseases in humans remains elusive. In this study, we used both immunohistochemistry and quantum dot (QD)-based immunofluorescence staining to investigate the expression of SIPA-1 in renal specimens from SLE and CC-RCC patients. MTT assay and Western blotting were employed to evaluate the effects of SIPA-1 overexpression on the proliferation and apoptosis of renal cell lines. Semi-quantitative reverse transcriptase-PCR (RT-PCR) was applied to examine the changes of hypoxia-inducible factor-1α (HIF-1α) mRNA level. Results showed that SIPA-1 was highly expressed in the proximal and collecting tubules of nephrons in SLE patients compared to normal ones, and similar results were obtained in the specimens of CC-RCC patients. Although SIPA-1 overexpression did not affect cellular proliferation and apoptosis of both human 786-O renal cell carcinoma cells and rat NRK-52E renal epithelial cell lines, RT-PCR results showed that HIF-1α mRNA level was down-regulated by SIPA-1 overexpression in 786-O cells. These findings suggest that SIPA-1 may play critical roles in the pathological changes in kidney, and might provide a new biomarker to aid in the diagnosis of SLE and CC-RCC.

The SIPA1 -313A>G polymorphism is associated with prognosis in inoperable non-small cell lung cancer

Polymorphism in signal-induced proliferation-associated 1 (SIPA1) gene may contribute to the development of metastasis in human cancers. In this preliminary study, we examined the association of the SIPA1 -313A>G (rs931127) polymorphism with overall survival (OS) and progression-free survival (PFS) in 351 inoperable patients with non-small cell lung cancer (NSCLC) treated with radiotherapy or radiochemotherapy (curative or palliative). The GG homozygotes had significantly shorter PFS under codominant and recessive models in all patients (hazard ratio (HR) 1.47, p = 0.035, and HR 1.47, p = 0.022, respectively) and in advanced stage subgroup (HR 1.49, p = 0.037, and HR 1.48, p = 0.023, respectively). The GG genotype was also associated with reduced OS and PFS (codominant model: HR 2.41, p = 0.020, and HR 2.34, p = 0.020, respectively; recessive model: HR 2.16, p = 0.026, and HR 2.18, p = 0.022, respectively) in radiotherapy alone subgroup. Moreover, the SIPA1 -313GG was identified as an independent adverse prognostic factor for PFS in the cohort. Our results indicate, for the first time, that the SIPA1 -313A>G may have a prognostic role in unresected NSCLC making it a potential predictor of poor survival due to earlier progression.

Use of pharmacogenetics for predicting cancer prognosis and treatment exposure, response and toxicity

Cancer treatment is complicated because of a multitude of treatment options and little patient-specific information to help clinicians choose appropriate therapy. There are two genomes relevant in cancer treatment: the tumor (somatic) and the patient (germline). Together, these two genomes dictate treatment outcome through four processes: the somatic genome primarily determines tumor prognosis and response while the germline genome modulates treatment exposure and toxicity. In this review, we describe the influence of these genomes on treatment outcomes by highlighting examples of genetic variation that are predictors of each of these four factors, prognosis, response, toxicity and exposure, and discuss the translation and clinical implementation of each. Use of pre-treatment pharmacogenetic testing will someday enable clinicians to make individualized therapy decisions about aggressiveness, drug selection and dose, improving treatment outcomes for cancer patients.

Sipa1 promoter polymorphism predicts risk and metastasis of lung cancer in Chinese

Signal-induced proliferation associated gene 1 (Sipa1) is a signal transducer to activate the Ras-related proteins and modulate cell progression, differentiation, adhesion and cancer metastasis. In this study, we tested the hypothesis that single nucleotide polymorphisms (SNPs) in Sipa1 are associated with lung cancer risk and metastasis. Three common SNPs (rs931127A > G, rs2448490G > A, and rs3741379G > T) were genotyped in a discovery set of southern Chinese population and then validated the promising SNPs in a validation set of an eastern Chinese population in a total of 1559 lung cancer patients and 1679 cancer-free controls. The results from the two sets were consistent, the rs931127GG variant genotype had an increased risk of lung cancer compared to the rs931127AA/GA genotypes (OR = 1.27; 95% CI = 1.09-1.49) after combination of the two populations, and the rs931127GG interacted with pack-year smoked on increasing lung cancer risk (P = 0.037); this SNP also had an effect on patients' clinical stages (P = 0.012) that those patients with the rs931127GG genotype had a significant higher metastasis rate and been advanced N, M stages at diagnosis. However, these associations were not observed for rs2448490G > A and rs3741379G > T in the discovery set. Our data suggest that the SNP rs931127A > G in the promoter of Sipa1 was significantly associated with lung cancer risk and metastasis, which may be a biomarker to predict the risk and metastasis of lung cancer.

Rap G protein signal in normal and disordered lymphohematopoiesis

Rap proteins (Rap1, Rap2a, b, c) are small molecular weight GTPases of the Ras family. Rap G proteins mediate diverse cellular events such as cell adhesion, proliferation, and gene activation through various signaling pathways. Activation of Rap signal is regulated tightly by several specific regulatory proteins including guanine nucleotide exchange factors and GTPase-activating proteins. Beyond cell biological studies, increasing attempts have been made in the past decade to define the roles of Rap signal in specific functions of normal tissue systems as well as in cancer. In the immune and hematopoietic systems, Rap signal plays crucial roles in the development and function of essentially all lineages of lymphocytes and hematopoietic cells, and importantly, deregulated Rap signal may lead to unique pathological conditions depending on the affected cell types, including various types of leukemia and autoimmunity. The phenotypical studies have unveiled novel, even unexpected functional aspects of Rap signal in cells from a variety of tissues, providing potentially important clues for controlling human diseases, including malignancy.

Association of SIPA1 545 C > T polymorphism with survival in Chinese women with metastatic breast cancer

It has been demonstrated that single nucleotide polymorphisms (SNPs) of SIPA1 (signal-induced proliferation associated gene 1) are associated with metastatic efficiency in both human and rodents. The purpose of this study was to determine whether SIPA1 545 C > T polymorphism was associated with overall survival in patients with metastatic breast cancer. In this study, SIPA1 545 C > T polymorphism was detected in 185 metastatic breast cancer patients using polymerase chain reaction-restriction fragment length polymorphism assay (PCR-RFLP). Survival curves for patients with SIPA1 545 C > T polymorphism was compared using the Kaplan-Meier method with log-rank tests. We found that SIPA1 545 C > T polymorphism was significantly associated with survival in 185 patients with metastatic breast cancer. Patients with SIPA1 545 T/T genotype had a significantly worse overall survival (OS) than did patients with C/T or C/C genotype (50.0% vs. 62.9%, P = 0.042). Moreover, in multivariate analysis, as compared with the C/C or C/T genotype, the T/T genotype remained an independent unfavorable prognostic marker of OS in this cohort (hazard ratio [HR] = 2.16; 95% CI = 1.12-4.15; P = 0.022). Our findings indicate that metastatic breast cancer patients with SIPA1 545 T/T genotype have a poorer survival compared to patients with C/C or C/T genotype.

p53 expression controls prostate cancer sensitivity to chemotherapy and the MDM2 inhibitor Nutlin-3

Prostate cancer is the second most commonly diagnosed cancer in men, and approximately one-third of those diagnosed succumb to the disease. The development of prostate cancer from small regions of hyperplasia to invasive tumors requires genetic and epigenetic alterations of critical cellular components to aid in the development of cells more adapted for aberrant growth. The p53 transcription factor is a critical element in the cell's ability to regulate the cell cycle and its response to DNA damage. Mutations within the DNA-binding domain of p53 are common and allow the formation of tetramers; however, these alterations prevent this protein complex from associating with target gene promoters. In the present study, we examined the effects of p53 functionality in prostate cancer cells that harbored wild-type (WT) or mutant forms of the protein in response to commonly used chemotherapeutic drugs. The androgen receptor positive 22Rv-1 and LNCaP prostate cancer cell lines carry WT p53 and were demonstrated to have a decrease in chemotherapeutic drug sensitivity when transfected with a dominant-negative (DN) p53. Conversely, expression of the WT p53 in the p53-mutated and more advanced DU145 prostate cancer cell line significantly increased its overall sensitivity to anti-neoplastic drugs. Furthermore, analysis of colony formation in soft agar revealed that the functional status of p53 in each cell line altered the cell's ability to proliferate in an anchorage-independent fashion. Prostate cancer colony growth was more prevalent when p53 transcriptional activity was decreased, whereas growth was more limited in the presence of functional p53. These results demonstrate that the functional status of the tumor suppressor p53 is important in the progression of prostate cancer and dictates the overall effectiveness a given drug would have on disease treatment.

Aggressiveness of human melanoma xenograft models is promoted by aneuploidy-driven gene expression deregulation

Melanoma is a devastating skin cancer characterized by distinct biological subtypes. Besides frequent mutations in growth- and survival-promoting genes like BRAF and NRAS, melanomas additionally harbor complex non-random genomic alterations. Using an integrative approach, we have analysed genomic and gene expression changes in human melanoma cell lines (N=32) derived from primary tumors and various metastatic sites and investigated the relation to local growth aggressiveness as xenografts in immuno-compromised mice (N=22). Although the vast majority >90% of melanoma models harbored mutations in either BRAF or NRAS, significant differences in subcutaneous growth aggressiveness became obvious. Unsupervised clustering revealed that genomic alterations rather than gene expression data reflected this aggressive phenotype, while no association with histology, stage or metastatic site of the original melanoma was found. Genomic clustering allowed separation of melanoma models into two subgroups with differing local growth aggressiveness in vivo. Regarding genes expressed at significantly altered levels between these subgroups, a surprising correlation with the respective gene doses (>85% accordance) was found. Genes deregulated at the DNA and mRNA level included well-known cancer genes partly already linked to melanoma (RAS genes, PTEN, AURKA, MAPK inhibitors Sprouty/Spred), but also novel candidates like SIPA1 (a Rap1GAP). Pathway mining further supported deregulation of Rap1 signaling in the aggressive subgroup e.g. by additional repression of two Rap1GEFs. Accordingly, siRNA-mediated down-regulation of SIPA1 exerted significant effects on clonogenicity, adherence and migration in aggressive melanoma models. Together our data suggest that an aneuploidy-driven gene expression deregulation drives local aggressiveness in human melanoma.

The conserved 12-amino acid stretch in the inter-bromodomain region of BET family proteins functions as a nuclear localization signal

The bromodomain and extraterminal (BET) family is a group of chromatin-binding proteins characterized by two bromodomains, an extraterminal (ET) domain, and several other conserved regions of unknown function. In humans, the BET family consists of four members, BRD2, BRD3, BRD4 and BRDT, that all normally localize to the nucleus. We identified a 12-amino acid stretch in the inter-bromodomain region that is perfectly conserved among the BET family members. We deleted these residues and expressed the mutant proteins in HEK293T cells to investigate the function of this motif. We found that the deletion of this motif alters the localization of BET proteins. Mutated BRD3 and BRD4 were excluded from the nucleus, and BRDT was found to be diffused throughout the nucleus and cytoplasm. Although the mutant BRD2 remained predominantly in the nucleus, a punctate distribution was also observed in the cytosol. It has been reported that a conserved motif between the second bromodomain and the ET domain serves as a nuclear localization signal for BRD2. Nevertheless, BET mutants lacking the reported nuclear localization signal motif but retaining the 12-amino acid stretch resided in the nucleus. Furthermore, these mutants were diffused throughout the cytoplasm when the 12 residues were removed. These results indicate that the conserved amino acid stretch in the inter-bromodomain region of the BET family functions as a nuclear localization signal.

Perturbation of microRNAs in rat heart during chronic doxorubicin treatment

Anti-cancer therapy based on anthracyclines (DNA intercalating Topoisomerase II inhibitors) is limited by adverse effects of these compounds on the cardiovascular system, ultimately causing heart failure. Despite extensive investigations into the effects of doxorubicin on the cardiovascular system, the molecular mechanisms of toxicity remain largely unknown. MicroRNAs are endogenously transcribed non-coding 22 nucleotide long RNAs that regulate gene expression by decreasing mRNA stability and translation and play key roles in cardiac physiology and pathologies. Increasing doses of doxorubicin, but not etoposide (a Topoisomerase II inhibitor devoid of cardiovascular toxicity), specifically induced the up-regulation of miR-208b, miR-216b, miR-215, miR-34c and miR-367 in rat hearts. Furthermore, the lowest dosing regime (1 mg/kg/week for 2 weeks) led to a detectable increase of miR-216b in the absence of histopathological findings or alteration of classical cardiac stress biomarkers. In silico microRNA target predictions suggested that a number of doxorubicin-responsive microRNAs may regulate mRNAs involved in cardiac tissue remodeling. In particular miR-34c was able to mediate the DOX-induced changes of Sipa1 mRNA (a mitogen-induced Rap/Ran GTPase activating protein) at the post-transcriptional level and in a seed sequence dependent manner. Our results show that integrated heart tissue microRNA and mRNA profiling can provide valuable early genomic biomarkers of drug-induced cardiac injury as well as novel mechanistic insight into the underlying molecular pathways.

Rap1 and its regulatory proteins: the tumor suppressor, oncogene, tumor suppressor gene axis in head and neck cancer

Squamous cell carcinoma of the head and neck (SCCHN) is the sixth most common cancer, globally. Previously, we showed that Rap1GAP is a tumor suppressor gene that inhibits tumor growth, but promotes invasion in SCCHN. In this work, we discuss the role of Rap1 and Rap1GAP in SCCHN progression in the context of a microRNA-oncogene-tumor suppressor gene axis, and investigate the role of Rap1GAP in EZH2-mediated invasion. Loss of expression of microRNA-101 in SCCHN leads to upregulation of EZH2, a histone methyltransferase. Overexpression of EZH2 silences Rap1GAP via methylation, thereby promoting activation of its target, Rap1. This microRNA-controlled activation of Rap1, via EZH2-mediated silencing of Rap1GAP, is a novel mechanism of Rap1 regulation. In two independent SCCHN cell lines, downregulation of EZH2 inhibits proliferation and invasion. In both cell lines, stable knockdown of EZH2 (shEZH2) recovers Rap1GAP expression and inhibits proliferation. However, siRNA-mediated knockdown of Rap1GAP in these cells rescues proliferation but not invasion. Thus, EZH2 promotes proliferation and invasion via Rap1GAP-dependent and -independent mechanisms, respectively. Although the studies presented here are in the context of SCCHN, our results may have broader implications, given that Rap1GAP acts as a tumor suppressor in pancreatic cancer, thyroid cancer, and melanoma.