Relaxin promotes differentiation of human breast cancer cells MCF-7 transplanted into nude mice

Relaxin gene therapy: A promising new treatment option for various diseases with aberrant fibrosis or irregular angiogenesis

Relaxin (RLX) is an insulin-like polypeptide hormone that was initially introduced for its pregnancy-related function. Subsequent studies revealed that RLX possesses anti-fibrotic functions in tumors and nonreproductive tissues, such as skin, lungs, and others. This aspect of the RLX has been explored for the treatment of various illnesses, such as cardiac fibrosis, liver fibrosis, and solid tumors. With gene therapy coming into age with increasing number of products being approved by regulatory bodies in Europe and United States, we aim to discuss how RLX have been utilized in scope of gene therapy for treatment of various illnesses.

Relaxin 2/RXFP1 Signaling Induces Cell Invasion via the β-Catenin Pathway in Endometrial Cancer

Relaxin is known to play an important role in animal pregnancies, including those of humans. It is suggested that relaxin induces aggressive cell growth and invasiveness in several types of cancer, including endometrial cancer. However, the mechanisms of relaxin remain largely unclear. In this study, we examined the effects of relaxin 2 (RLN2), the major circulating relaxin in humans, on human endometrial carcinoma cell lines. RLN2 treatment induced invasion in HEC-1B and Ishikawa cells. RLN2-induced cell invasion was significantly decreased by transfection of relaxin receptor 1 (RXFP1) siRNAs. The β-catenin inhibitor, XAV939, also significantly inhibited the RLN2-induced cell invasions. Both a decrease of cadherin expression and an increase of β-catenin phosphorylation were observed in response to the RLN2 treatment in HEC-1B and Ishikawa cells. We then examined RLN2 and RXFP1 expression in 80 human endometrioid endometrial carcinoma tissues. RLN2 immunoreactivity was detected in the human endometrial carcinoma cells and had a correlative tendency with histological grade and RXFP1. These results suggest that adherens junctions in cancer cells are weakened by the breakdown of the cadherin/catenin complex, which is induced by β-catenin phosphorylation via RLN2/RXFP1 signaling.

Relaxins enhance growth of spontaneous murine breast cancers as well as metastatic colonization of the brain

Relaxins are known for their tissue remodeling capacity which is also a hallmark of cancer progression. However, their role in the latter context is still unclear, particularly in breast cancer. In a mouse model with spontaneously arising breast cancer due to erbB2-overexpression we show that exposure to porcine relaxin results in significantly enhanced tumour growth as compared to control animals. This is accompanied by increased serum concentrations of progesterone and estradiol as well as elevated expression of the respective receptors and the relaxin receptor RXFP1 in the tumour tissue. It is also associated with enhanced infiltration by tumour-associated macrophages which are known to promote tumour progression. Additionally, we show in an ex vivo model of metastatic brain colonization that porcine relaxin as well as human brain-specific relaxin-3 promotes invasion into the brain tissue and enhance interaction of breast cancer cells with the resident brain macrophages, the microglia. Relaxin signaling is mediated via RXFP1, since R 3/I5, a specific agonist of the relaxin-3 receptor RXFP3 in the brain, does not significantly enhance invasion. Taken together, these findings strongly support a role of relaxins in the progression of breast cancer where they foster primary tumour growth as well as metastatic colonization by direct and indirect means.

Relaxin reduces xenograft tumour growth of human MDA-MB-231 breast cancer cells

Introduction

Relaxin levels are increased in cases of human breast cancer and has been shown to promote cancer cell migration in carcinoma cells of the breast, prostate gland and thyroid gland. In oestrogen receptor alpha-negative MDA-MB-231 human breast cancer cells, relaxin was shown to down-regulate the metastasis-promoting protein S100A4 (metastasin), a highly significant prognostic factor for poor survival in breast cancer patients. The cellular mechanisms of relaxin exposure in breast cancer cells are not fully understood. The aim of this study was to investigate short-term and long-term effects of relaxin on cancer cell motility and S100A4 expression and to determine the long-term effects of relaxin on in vivo tumour growth in an oestrogen-independent context.

Method

We have established stable transfectants of highly invasive oestrogen-receptor alpha-negative MDA-MB-231 human breast cancer cells with constitutive expression of bioactive H2-relaxin (MDA/RLN2). RLN2 secretion was determined by ELISA. Relaxin receptor RXFP1 (Relaxin-family-peptide) was detected by reverse transcription (RT) PCR and its activation was assessed by induction of cyclic adenosine monophosphate (cAMP). Stable MDA/RLN2 clones and RLN2 treated MDA-MB-231 cells were subjected to motility and in vitro-invasion assays. Proliferation was assessed in bromodeoxyuridine (BrdU) and MTT assays. S100A4 expression was determined by RT-PCR and Western blot. Specific small interfering RNA was employed to down-regulate relaxin receptor and S100A4. MDA/EGFP vector control and two MDA/RLN2 clones were injected subcutaneously in nude mice to determine tumour growth and cancer cell invasiveness in vivo. Xenograft tumour tissues were assessed by histology and immunohistochemistry and frozen tissues were used for the detection of S100A4 and RLN2.

Results

Short-term exposure to relaxin for 24 hours increased cell motility in a relaxin receptor-dependent manner. This increase in cell motility was mediated by S100A4. Long-term exposure to relaxin secreted from stable transfectants reduced cell motility and in vitro invasiveness. Relaxin decreased cell proliferation and down-regulated cellular S100A4 levels in MDA-MB-231 and T47D breast cancer cells. Stable MDA/RLN2 transfectants produced smaller xenograft tumours containing reduced S100A4 protein levels in vivo.

Conclusion

Our results indicate that long-term exposure to relaxin confers growth inhibitory and anti-invasive properties in oestrogen-independent tumours in vivo, which may in part be mediated through a down-regulation of S100A4.

Relaxin promotes prostate cancer progression

PURPOSE

To understand the role of relaxin peptide in prostate cancer, we analyzed the expression of relaxin and its receptor in human prostate cancer samples, the effects of relaxin signaling on cancer cell phenotype in vitro, and the effects of increased serum relaxin concentrations on cancer progression in vivo.

EXPERIMENTAL DESIGN

The relaxin and its receptor leucine-rich repeat containing G protein-coupled receptor 7 (LGR7) expression were studied by quantitative reverse transcription-PCR (11 benign and 44 cancer tissue samples) and by relaxin immunohistochemistry using tissue microarrays containing 10 normal and 69 cancer samples. The effects of relaxin treatment and endogenous relaxin/LGR7 suppression via short interfering RNA in PC-3 and LNCaP cells were analyzed in vitro. The effect of transgenic relaxin overexpression [Tg(Rln1)] on cancer growth and survival was evaluated in autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP).

RESULTS

The relaxin mRNA expression was significantly higher in recurrent prostate cancer samples. In tissue microarrays of the 10 normal tissues, 8 had low staining in epithelial cells, whereas only 1 of 9 high-grade prostatic intraepithelial neoplasia lesions had low expression (P = 0.005) and only 29 of 65 cancers had low expression (P = 0.047). Stimulation with relaxin increased cell proliferation, invasiveness, and adhesion in vitro. The suppression of relaxin/LGR7 via short interfering RNAs decreased cell invasiveness by 90% to 95% and growth by 10% to 25% and increased cell apoptosis 0.6 to 2.2 times. The Tg(Rln1) TRAMP males had shorter median survival time, associated with the decreased apoptosis of tumor cells, compared with non-Tg(Rln1) TRAMP animals.

CONCLUSIONS

Relaxin signaling plays a role in prostate cancer progression.

Relaxin becomes upregulated during prostate cancer progression to androgen independence and is negatively regulated by androgens

BACKGROUND

Relaxin is a potent peptide hormone normally secreted by the prostate. This study characterized relaxin expression during prostate cancer progression to androgen independence (AI), and in response to androgens.

METHODS

The prostate cancer cell line, LNCaP, was assayed by microarrays and confirmatory Northern analysis to assess changes in relaxin levels due to androgen treatment and in LNCaP xenografts following castration. Relaxin protein levels were examined by immunohistochemistry (IHC) in tissue microarrays of human prostate cancer samples following androgen ablation.

RESULTS

Relaxin levels decreased in a time and concentration-dependent manner due to androgens in vitro, and increased in xenografts post-castration. Relaxin increased in radical prostatectomy specimens after 6 months of androgen ablation and in AI tumors, was highest in bone metastases.

CONCLUSIONS

Relaxin is negatively regulated by androgens in vitro and in vivo, which correlates to clinical prostate cancer specimens following androgen ablation. The role of relaxin in angiogenesis and tissue remodeling suggests it may contribute to prostate cancer progression.

Relaxin—a pleiotropic hormone and its emerging role for experimental and clinical therapeutics

The insulin-related peptide hormone relaxin (Rlx) is known as pregnancy hormone for decades. In the 1980s, researchers began to recognize the highly intriguing fact that Rlx plays a role in a multitude of physiological processes far beyond pregnancy and reproduction. So, Rlx's contribution to the regulation of vasotonus, plasma osmolality, angiogenesis, collagen turnover, and renal function has been established. In addition, the peptide has been demonstrated to represent a mediator of cardiovascular pathology. The ongoing efforts to identify Rlx receptors eventually precipitated the discovery of the G protein-coupled receptors (GPCR) LGR7 and LGR8 as membrane receptors for human Rlx-2 in 2002. This review will summarize the current state of insight into this rapidly evolving field, which has further been expanded by the discovery of GPCR135 and GPCR142 as receptors for Rlx-3. In addition, Rlx has also been shown to activate the human glucocorticoid receptor (GR). There is evidence from Rlx and Rlx receptor knockouts suggesting that LGR7 is the only relevant receptor for mouse Rlx-1 (corresponding to human Rlx-2) in vivo and that insulin-like peptide (INSL)-3 represents the physiological ligand for LGR8. Regarding Rlx signal transduction, the cyclic adenosine monophosphate (cAMP) and nitric oxide (NO) pathways will be characterized as major cascades. Investigation of downstream signaling remains an important field for future research. Finally, the current state of therapeutical strategies using Rlx in animal models as well as in humans is summarized.

Relaxin Downregulates the Calcium Binding Protein S100A4 in MDA-MB-231 Human Breast Cancer Cells

Expressed in the human breast and in human breast cancer tissues, the heterodimeric peptide hormone relaxin is involved in extracellular matrix turnover. To investigate the role of relaxin in estrogen receptor-alpha negative human breast cancer cells, we established transfectants of the human MDA-MB-231 breast cancer cell line stably overexpressing H2-relaxin (MDA-MB-231/pIRES-EGFP-H2). These transfectants produced and secreted functional relaxin. Our investigations revealed downregulation of mRNA and protein of the calcium binding protein S100A4 (metastasin) in MDA-MB-231/pIRES-EGFP-H2 transfectants, indicating a distinct and novel role for relaxin in estrogen receptor-alpha negative human breast cancer cells.

Photonic Monitoring in Real Time of Vascular Endothelial Growth Factor Receptor 2 Gene Expression under Relaxin-Induced Conditions in a Novel Murine Wound Model

Relaxin is known to promote vascular endothelial growth factor (VEGF) expression in reproductive tissue, and successful wound healing depends on good vascularization of wound sites, a process that relaxin may facilitate. Thus, the objective of this study was to evaluate the efficacy of relaxin on the development of vascular tissue at wound sites in a novel VEGF receptor 2-luc (VEGFR2-luc) transgenic mouse wound model by monitoring the rate of VEGFR2-luc-mediated gene expression using bioluminescence and real-time imaging. To this end, 12 FVB/N VEGFR2-luc transgenic male mice were assigned to treatments (six per group): saline alone or relaxin (1 g/6 h/14 days) administered intraperitoneally (i.p.). On day 0, a set of full-thickness wounds (6-mm punch) were generated under anesthesia on the dorsal aspect of each mouse. Photonic emissions were recorded (5-min collection of photons) from wound sites 10 min after the administration of luciferin (150 mg/kg i.p.) on day 0 and on days 1, 2, 4, 7, 9, 11, and 14 postwounding to quantify luciferase activity using an IVIS 100 biophotonic imaging system. Animals were sacrificed (three per group) on day 7 or 14, and wound tissue specimens were recovered for molecular and histologic analyses. Although photonic emission from wound sites increased (P < .001) over time with peak values obtained by day 7, no significant (P > .05) effect of relaxin treatment on VEGFR2-luc gene expression was noted at wound sites. Whereas measuring relaxin's effect on angiogenesis indirectly via the VEGFR2 model was not successful, photonic imaging provides an exciting new tool using alternative models (i.e., VEGF-luc mouse) to study relaxin-induced gene expression in normal (i.e., wound healing) or tumorigenic tissues in real time.

Relaxin stimulates protein kinase C zeta translocation: requirement for cyclic adenosine 3',5'-monophosphate production

Relaxin is a polypeptide hormone that activates the leucine-rich repeat containing G protein-coupled receptors, LGR7 and LGR8. In an earlier study, we reported that relaxin produces a biphasic time course and the second wave of cAMP is highly sensitive to phosphoinositide-3 kinase inhibitors (LY294002 and wortmannin). LY294002 inhibits relaxin-mediated increases in cAMP production by 40-50% across a large range of relaxin concentrations. Here we show that protein kinase C zeta (PKCzeta) is a component of relaxin signaling in THP-1 cells. Sphingomyelinase increases cAMP production due to the release of ceramide, a direct activator of PKCzeta. Chelerythrine chloride (a general PKC inhibitor) inhibits relaxin induced cAMP production to the same degree (approximately 40%) as LY294002. Relaxin stimulates PKCzeta translocation to the plasma membrane in THP-1, MCF-7, pregnant human myometrial 1-31, and mouse mesangial cells, as shown by immunocytochemistry. PKCzeta translocation is phosphoinositide-3 kinase dependent and independent of cAMP production. Antisense PKCzeta oligodeoxynucleotides (PKCzeta-ODNs) deplete both PKCzeta transcript and protein levels in THP-1 cells. PKCzeta-ODNs abolish relaxin-mediated PKCzeta translocation and inhibit relaxin stimulation of cAMP by 40%, as compared with mock and random ODN controls. Treatment with LY294002 in the presence of PKCzeta-ODNs results in little further inhibition. In summary, we present a novel role for PKCzeta in relaxin-mediated stimulation of cAMP.

Elevated Concentrations of Serum Relaxin are Associated with Metastatic Disease in Breast Cancer Patients

Relaxin (RLX) is known to induce remodeling of benign stromal tissues through upregulation of matrix metalloproteases (MMPs). Recently, we could show that RLX also induces MMPs in breast cancer cells and enhances in vitro invasiveness. To investigate its potential role for progression of breast cancer in vivo, RLX serum concentrations were determined in 160 breast cancer patients during post-surgical follow-up. RLX concentrations in cancer patients were significantly higher than in a control population of healthy blood donors and patients with various other diseases (0.47 versus 0.29 ng/ml, p < 0.0001). There was a significant difference between patients with metastases (0.62 ng/ml) and those without (0.38 ng/ml, p < 0.0001). Overall survival was shorter in RLX-positive ( > 0.4 ng/ml) than in RLX-negative patients (p = 0.016). Cox regression analysis showed that RLX was not an independent variable, in contrast to metastatic disease and primary lymph node involvement. Taken together, the detection of elevated RLX concentrations especially in patients with metastases supports the assumption that there is a role for RLX in tissue remodeling during breast cancer progression.

Cadherins in cancer

The presence of a functional E-cadherin/catenin cell-cell adhesion complex is a prerequisite for normal development and maintenance of epithelial structures in the mammalian body. This implies that the acquisition of molecular abnormalities that disturb the expression or function of this complex is related to the development and progression of most, if not all, epithelial cell-derived tumors, i.e. carcinomas. E-cadherin downregulation is indeed correlated with malignancy parameters such as tumor progression, loss of differentiation, invasion and metastasis, and hence poor prognosis. Moreover, E-cadherin has been shown to be a potent invasion suppressor as well as a tumor suppressor. Disturbed expression profiles of the E-cadherin/catenin complex have been demonstrated in histological sections of many human tumor types. In different kinds of carcinomas, biallelic downregulation of the E-cadherin gene, resulting in tumor-restricted decrease or even complete loss of E-cadherin expression, appears to be caused by a variety of inactivation mechanisms. Gene deletion due to loss of heterozygosity of the CDH1 locus on 16q22.1 frequently occurs in many carcinoma types. However, somatic inactivating mutations resulting in aberrant E-cadherin expression by loss of both wild-type alleles is rare and restricted to only a few cancer types. A majority of carcinomas thus seems to show deregulated E-cadherin expression by other mechanisms. The present evidence proposes transcriptional repression as a powerful and recurrent molecular mechanism for silencing E-cadherin expression. The predominant mechanisms emerging in most carcinomas are hypermethylation of the E-cadherin promoter and expression of transrepressor molecules such as SIP1, Snail, and Slug that bind sequence elements in the proximal E-cadherin promoter. Interestingly, complex differential expression of other cadherins seems to be associated with loss of E-cadherin and to reinforce effects of this loss on tumor progression. Multiple agents can upregulate and stabilize the E-cadherin/catenin complex. Especially for those tumors with transcriptional and thus reversible downregulation of E-cadherin expression, these drug agents offer important therapeutic opportunities.

Relaxin-like peptides in cancer

The members of the relaxin-like hormone family, relaxin and INSL3, also known as relaxin-like factor (RLF) or Leydig cell-derived insulin-like factor (LEY-I-L), are implicated in various mechanisms associated with tumor cell growth, differentiation, invasion and neovascularization. The recent discovery of the relaxin receptor LGR7 and the INSL3/relaxin receptor LGR8 has provided evidence of an auto/paracrine relaxin-like action in tumor tissues and enables the elucidation of the cellular pathways involved in the proposed functions of relaxin in tumor biology. Our review summarizes our current knowledge of the expression of relaxin and INSL3 in human neoplastic tissues and discusses the etiological roles of these heterodimeric peptide hormones in cancer. Discussion of possible cellular cascades involved in actions linking relaxin-like peptides and neoplasia include the role of relaxin-like peptides in tumor cell growth and differentiation; the effect of relaxin in stimulating the synthesis of the vasodilatory and tumor cell cytostatic and antiapoptotic molecule, nitric oxide; the potential ability of relaxin to upregulate vascular endothelial growth factor to promote angiogenesis and neovascularization and the concerted fine-tuned action of relaxin on the matrix metalloproteinases on the extracellular matrix to facilitate tumor cell attachment, migration and invasion.

Adenovirus-mediated expression of human prorelaxin promotes the invasive potential of canine mammary cancer cells

This study reports the characterization of a recombinant adenoviral vector containing a tetracycline-regulatable promoter, driving the bicistronic expression of the human H2 preprorelaxin (hH2) cDNA and enhanced green fluorescent protein, via an internal ribosomal entry site. An hH2 ELISA was used to measure the secreted levels of recombinant hH2 in transfected canine (CF33.Mt) and human (MDA-MB-435) mammary cancer cell lines over a 6-d period; secreted peptide peaked on d 2 and 4 for the canine and human cell types, respectively. An unprocessed hH2 immunoreactive form of approximately 18 kDa was identified by Western blotting analysis and confirmed by mass spectrometry, suggesting that prorelaxin remains unprocessed in these cell types. The biological activity of the adenovirally expressed human prorelaxin was measured in the established human monocytic cell line THP-1 cAMP ELISA and in an in vitro Transwell cell migration system. Exogenous recombinant hH2 and adenovirally-mediated delivery of prorelaxin to CF33.Mt cells conferred a significant migratory action in the cells, compared with controls. Cell proliferation assays were performed to discount the possibility that the effect of relaxin was mitogenic. Thus, we have demonstrated that prorelaxin has the ability to facilitate cell migration processes exclusive of its ability to stimulate cell proliferation. In validating this adenovirus-based system, we have created a potential tool for further exploration of the physiology of relaxin in mammalian systems.

JNK/SAPK mediates doxorubicin-induced differentiation and apoptosis in MCF-7 breast cancer cells

Pharmacologic induction of cancer cell differentiation has potential in the treatment of breast cancer. Doxorubicin, a widely used anthracycline antibiotic, was previously reported to induce differentiation of MCF-7 breast cancer cells. We demonstrate in this study that inhibition of MCF-7 breast cancer cell growth by low dose doxorubicin (0.01 microg/ml) was accompanied by an increase in cytokeratin 8/18 and milk fat globule membrane protein expression, biomarkers for differentiation of breast cancer, as well as an increase in JNK/SAPK phosphorylation. High dose doxorubicin (10.0 microg/ml) induced apoptosis in these cells. Overexpression of dominant-inhibitory forms of JNK1 and c-Jun blocked both the differentiation and apoptotic effects of doxorubicin. These results suggest that JNK/SAPK pathway signaling plays a prominent role in doxorubicin-induced cell cycle withdrawal, differentiation and control of apoptosis in this cell system. These findings support the possibility that JNK/SAPK pathway activation may be a means of therapeutic intervention in breast cancer.

Relaxin peptides are new global players

Relaxin (RLX) has come of age. From being one of the earliest hormones described with a very specific function in parturition, recent research has now shown that it is involved in a variety of roles, from endometrial differentiation during embryo implantation, to being a response factor in infarct and wound situations. It ameliorates fibrosis, and might also be involved in tumour growth and progression. And it is not alone: two other closely related peptide hormones have recently been identified, one specific for the brain, the other with roles in testicular descent and ovarian apoptosis. Finally, the recent cloning of the RLX receptors now provides the basis for a new molecular pharmacology for these peptide hormones, and preliminary studies suggest that their signal transduction is both interesting and unusual.