Breast cancer. Cyr61 is overexpressed, estrogen-inducible, and associated with more advanced disease

Identification of a novel integrin alpha 6 beta 1 binding site in the angiogenic inducer CCN1 (CYR61)

The angiogenic inducer CCN1 (cysteine-rich 61, CYR61), a secreted matricellular protein of the CCN family, is a ligand of multiple integrins, including alpha 6 beta 1. Previous studies have shown that CCN1 interaction with integrin alpha 6 beta 1 mediates adhesion of fibroblasts, endothelial cells, and smooth muscle cells, as well as migration of smooth muscle cells. Recently, we have reported that CCN1-induced tubule formation of unactivated endothelial cells is also mediated through integrin alpha 6 beta 1. In this study, we demonstrate that human skin fibroblasts adhere specifically to the T1 sequence (GQKCIVQTTSWSQCSKS) within domain III of CCN1, and this process is blocked by anti-alpha 6 and anti-beta 1 monoclonal antibodies. Alanine substitution mutagenesis of the T1 sequence further defines the sequence TTSWSQCSKS as the critical determinant for mediating alpha 6 beta 1-dependent adhesion. Soluble T1 peptide specifically inhibits fibroblast adhesion to CCN1 in a dose-dependent manner. Furthermore, T1 also inhibits cell adhesion to other alpha 6 beta 1 ligands, including CCN2 (CTGF), CCN3 (NOV), and laminin, but not to ligands of other integrins. In addition, T1 specifically inhibits alpha 6 beta 1-dependent tubule formation of unactivated endothelial cells in a CCN1-containing collagen gel matrix. To confirm that T1 binds integrin alpha 6 beta 1 directly, we perform affinity chromatography and show that integrin alpha 6 beta 1 is isolated from an octylglucoside extract of fibroblasts on T1-coupled Affi-gel. Taken together, these findings define the T1 sequence in CCN1 as a novel binding motif for integrin alpha 6 beta 1, providing the basis for the development of peptide mimetics to examine the functional role of alpha 6 beta 1 in angiogenesis.

A structural approach to the role of CCN (CYR61/CTGF/NOV) proteins in tumourigenesis

The CCN (CYR61 [Cystein-rich61]/CTGF [connective tissue growth factor]/NOV [Nephroblastoma overexpressed]) proteins constitute a family of regulatory factors involved in many aspects of cell proliferation and differentiation. An increasing body of evidence indicates that abnormal expression of the CCN proteins is associated to tumourgenesis. The multimodular architecture of the CCN proteins, and the production of truncated isoforms in tumours, raise interesting questions regarding the participation of each individual module to the various biological properties of these proteins. In this article, we review the current data regarding the involvement of CCN proteins in tumourigenesis. We also attempt to provide structural basis for the stimulatory and inhibitory functions of the full length and truncated CCN proteins that are expressed in various tumour tissues.

Two domains of the progesterone receptor interact with the estrogen receptor and are required for progesterone activation of the c-Src/Erk pathway in mammalian cells

In breast cancer cells, estrogens activate the Src/Erk pathway through an interaction of the estrogen receptor alpha (ERalpha) with the SH2 domain of c-Src. Progestins have been reported to activate also this pathway either via an interaction of the progesterone receptor isoform B (PRB) with ERalpha, which itself activates c-Src, or by direct interaction of PRB with the SH3 domain of c-Src. Here we identify two domains of PRB, ERID-I and -II, mediating a direct interaction with the ligand-binding domain of ERalpha. ERID-I and ERID-II flank a proline cluster responsible for binding of PRB to c-Src. In mammalian cells, the interaction of PRB with ERalpha and the progestin activation of the Src/Erk cascade are abolished by deletion of either ERID-I or ERID-II. These regions are not required for transactivation of a progesterone-responsive reporter gene. Mutations in the proline cluster of PRB that prevent a direct interaction with c-Src do not affect the strong activation of c-Src by progestins in the presence of ERalpha. Thus, in cells with ERalpha, ERID-I and ERID-II are necessary and sufficient for progestin activation of the endogenous Src/Erk pathway.

CYR61 (CCN1) is essential for placental development and vascular integrity

CYR61 (CCN1) is a member of the CCN family of secreted matricellular proteins that includes connective tissue growth factor (CCN2), NOV (CCN3), WISP-1 (CCN4), WISP-2 (CCN5), and WISP-3 (CCN6). First identified as the product of a growth factor-inducible immediate-early gene, CYR61 is an extracellular matrix-associated angiogenic inducer that functions as a ligand of integrin receptors to promote cell adhesion, migration, and proliferation. Aberrant expression of Cyr61 is associated with breast cancer, wound healing, and vascular diseases such as atherosclerosis and restenosis. To understand the functions of CYR61 during development, we have disrupted the Cyr61 gene in mice. We show here that Cyr61-null mice suffer embryonic death: approximately 30% succumbed to a failure in chorioallantoic fusion, and the reminder perished due to placental vascular insufficiency and compromised vessel integrity. These findings establish CYR61 as a novel and essential regulator of vascular development. CYR61 deficiency results in a specific defect in vessel bifurcation (nonsprouting angiogenesis) at the chorioallantoic junction, leading to an undervascularization of the placenta without affecting differentiation of the labyrinthine syncytiotrophoblasts. This unique phenotype is correlated with impaired Vegf-C expression in the allantoic mesoderm, suggesting that CYR61-regulated expression of Vegf-C plays a role in vessel bifurcation. The genetic and molecular basis of vessel bifurcation is presently unknown, and these findings provide new insight into this aspect of angiogenesis.

Pro-angiogenic activities of CYR61 (CCN1) mediated through integrins alphavbeta3 and alpha6beta1 in human umbilical vein endothelial cells

CYR61 (CCN1) is an extracellular matrix-associated protein of the CCN family, which also includes CTGF (CCN2), NOV (CCN3), WISP-1 (CCN4), WISP-2 (CCN5), and WISP-3 (CCN6). Purified CYR61 induces neovascularization in corneal implants, and Cyr61-null mice suffer embryonic death due to vascular defects, thus establishing that CYR61 is an important regulator of angiogenesis. Aberrant expression of Cyr61 is associated with breast cancer, wound healing, and vascular diseases such as atherosclerosis and restenosis. In culture, CYR61 functions through integrin-mediated pathways to promote cell adhesion, migration, and proliferation. Here we show that CYR61 can also promote cell survival and tubule formation in human umbilical vein endothelial cells. Furthermore, we have dissected the integrin receptor requirements of CYR61 with respect to its pro-angiogenic activities. Thus, CYR61-induced cell adhesion and tubule formation occur through interaction with integrin alpha(6)beta(1) in early passage endothelial cells in which integrins have not been activated. By contrast, in endothelial cells in which integrins are activated by phorbol ester or vascular endothelial growth factor, CYR61-promoted cell adhesion, migration, survival, growth factor-induced mitogenesis, and endothelial tubule formation are all mediated through integrin alpha(v)beta(3). These findings indicate that CYR61 is an activation-dependent ligand of integrin alpha(v)beta(3) and an activation-independent ligand of integrin alpha(6)beta(1) and that these integrins differentially mediate the pro-angiogenic activities of CYR61. These findings help to define the mechanisms by which CYR61 acts as an angiogenic regulator, provide a molecular interpretation for the loss of vascular integrity and increased apoptosis of vascular cells in Cyr61-null mice, and underscore the importance of CYR61 in the development and homeostasis of the vascular system.

Cyr61 promotes breast tumorigenesis and cancer progression

Cyr61, a member of the CCN family of genes, is an angiogenic factor. We have shown that it is overexpressed in invasive and metastatic human breast cancer cells and tissues. Here, we investigated whether Cyr61 is necessary and/or sufficient to bypass the 'normal' estrogen (E2) requirements for breast cancer cell growth. Our results demonstrate that Cyr61 is sufficient to induce MCF-7 cells to grow in the absence of E2. Cyr61-transfected MCF-7 cells (MCF-7/Cyr61) became E2-independent but still E2-responsive. On the other hand, MCF-7 cells transfected with the vector DNA (MCF-7/V) remain E2-dependent. MCF-7/Cyr61 cells acquire an antiestrogen-resistant phenotype, one of the most common clinical occurrences during breast cancer progression. MCF-7/Cyr61 cells are anchorage-independent and capable of forming Matrigel outgrowth patterns in the absence of E2. ER alpha expression in MCF-7/Cyr61 cells is decreased although still functional. Moreover, MCF-7/Cyr61 cells are tumorigenic in ovariectomized athymic nude mice. The tumors resemble human invasive carcinomas with increased vascularization and overexpression of vascular endothelial growth factor (VEGF). Our results demonstrate that Cyr61 is a tumor-promoting factor and a key regulator of breast cancer progression. This study provides evidence that Cyr61 is sufficient to induce E2-independence and antiestrogen-resistance, and to promote invasiveness in vitro, and to induce tumorigenesis in vivo, all of which are characteristics of an aggressive breast cancer phenotype.

Cyr61 and CTGF are molecular markers of bladder wall remodeling after outlet obstruction

Cysteine-rich protein (Cyr61) and connective tissue growth factor (CTGF) are key immediate early growth factors with functions in cell proliferation, differentiation, and extracellular matrix synthesis. Studies were performed to assess the gene expression profile of Cyr61 and CTGF in rat urinary bladder during growth in response to partial outlet obstruction. The mRNA levels of Cyr61 as determined by ribonuclease protection assay increased sharply after 1 day and remained elevated throughout the time period of the obstruction. This correlates well with increased bladder weight. The CTGF mRNA levels seemed to peak within the second week of the urethral obstruction and correlate well with increased type I collagen mRNA. The expression pattern of either Cyr61 or CTGF proteins corroborated that of their respective mRNAs. Immunohistochemical analyses showed that immunoreactivity of Cyr61 was confined to detrusor smooth muscle and that of CTGF was detected within both detrusor muscle and lamina propria layers. These data strongly indicate the involvement of Cyr61 and CTGF in bladder wall remodeling as a result of the outlet obstruction.

Gene expression during the priming phase of liver regeneration after partial hepatectomy in mice

Understanding the gene-expression patterns during liver regeneration may help to reveal how regenerative processes are initiated and controlled as well as shed new light onto processes that lead to liver disease. Using high-density oligonucleotide arrays, we have examined the gene-expression program in the livers of mice after partial hepatectomy. A time course was constructed for gene expression between 0 and 4 h after partial hepatectomy, corresponding to the priming phase of liver regeneration. The genomic program for liver regeneration involves transcription-factor generation, stress and inflammatory responses, cytoskeletal and extracellular matrix modification, and regulation of cell-cycle entry. The genome-wide changes that are observed provide a detailed and comprehensive map of the initial priming stage of liver regeneration.

Expression of CYR61, an angiogenic immediate early gene, in arteriosclerosis and its regulation by angiotensin II

BACKGROUND

The renin-angiotensin system is thought to be involved in development and progression of arteriosclerosis, thereby contributing to adverse cardiovascular events. To elucidate the role of angiotensin II (Ang II) at a cellular level, we analyzed the Ang II-induced gene expression profile.

METHODS AND RESULTS

Genes induced on Ang II stimulation (10(-7) mol/L, 45 minutes) in rat smooth muscle cells were analyzed by polymerase chain reaction selected subtraction. In addition to known genes, such as interleukin 6, leukemia inhibitory factor, and c-fos, we identified CYR61, an angiogenic immediate early gene. Northern blot analysis revealed a rapid 2.5-fold increase of CYR61 transcript levels by Ang II, peaking at 30 minutes, which was blunted by Ang II type 1 receptor blockade. Exposure of rat aortic rings to Ang II (30 minutes) revealed a 2-fold, and intraperitoneal injection of Ang II (30 minutes) in mice a 3-fold, increase of aortic CYR61 transcripts. In arteriosclerotic aortas of apolipoprotein E-deficient mice, CYR61 transcripts confirmed by in situ hybridization and proteins shown by immunohistochemistry were elevated, whereas they were hardly detectable in wild types. In human carotid atherectomies and arteriosclerotic coronary arteries, immunohistochemical analysis revealed expression of CYR61 within connective tissue in neointima, adventitia, and surrounding small capillaries and blood vessels, colocalized with ACE and Ang II. Normal human arteries showed no significant staining for CYR61.

CONCLUSIONS

CYR61, an angiogenic factor, is induced by Ang II in vascular cells and tissue. The expression of CYR61, colocalized with Ang II and ACE, in small vessels of human arteriosclerotic lesions is consistent with the notion that the activated renin-angiotensin system may contribute to plaque neovascularization by enhancing regulators of microvessel formation and cell proliferation.

The angiogenic factor cysteine-rich 61 (CYR61, CCN1) supports vascular smooth muscle cell adhesion and stimulates chemotaxis through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans

Cysteine-rich 61 (CYR61, CCN1) is a heparin-binding, extracellular, matrix-associated protein of the cysteine-rich 61/nephroblastoma family, which also includes connective tissue growth factor, nephroblastoma overexpressed, Wnt-induced secreted protein-1 (WISP-1), WISP-2, and WISP-3. CYR61 induces angiogenesis in vivo and supports cell adhesion, promotes cell migration, and enhances growth factor-stimulated mitogenesis in fibroblasts and endothelial cells. Although the expression of CYR61 has been observed in arterial walls, its function in vascular smooth muscle cells (VSMCs) has not been examined to date. Here we show that purified CYR61 supports VSMC adhesion in a dose-dependent, saturable manner through integrin alpha(6)beta(1) with an absolute requirement of cell surface heparan sulfate proteoglycans. In addition, CYR61 induces VSMC chemotaxis, but not chemokinesis, through integrin alpha(6)beta(1) and heparan sulfate proteoglycans. Heparin-binding defective CYR61 mutants are unable to support VSMC adhesion but can still induce chemotaxis at a reduced level. Following balloon angioplasty in rat carotid artery, CYR61 protein level is elevated in the media and neointima of the injured vessel by d 4 post angioplasty, peaks from d 7 to 14, and remains high for at least 28 d. These data demonstrate the activities of CYR61 in VSMCs, identify the receptors that mediate its functions, and show that CYR61 is synthesized in arterial smooth muscle walls during proliferative restenosis. Together, these results implicate CYR61 as a novel factor that modulates the responses of VSMCs to vascular injury.

Expression and regulation of Cyr61 in human breast cancer cell lines

We have shown that Cyr61, an angiogenic regulator, is overexpressed in invasive and metastatic human breast cancer cells and tumor biopsies. We have further demonstrated that Cyr61 promotes acquisition of estrogen-independence and anti-estrogen resistance in vivo in breast cancer cells. Moreover, we have demonstrated that Cyr61 induces tumor formation and tumor vascularization in vivo, events mediated through the activation of the MAPK and the Akt signaling pathways. Here we investigate how Cyr61 expression is regulated in both estrogen receptor (ER)-positive and ER-negative breast cancer cells. We demonstrate that Cyr61 mRNA and protein expression is inducible by estrogen and anti-estrogens in ER-positive breast cancer cells. We show that a labile protein as well as a negative regulator might be involved in Cyr61 expression in estrogen-dependent breast cancer cells. Other important regulators of Cyr61 expression in breast cancer cells that we found are the phorbol ester TPA, vitamin D, and retinoic acid. TPA causes positive regulation of Cyr61 expression in ER-positive MCF-7 cells. Vitamin D induces a transient stimulatory effect on Cyr61 gene expression. Lastly, retinoic acid has a negative effect on Cyr61 expression and downregulates its expression in MCF-7 cells. Interestingly, most of these effects are not seen in aggressive breast cancer cells that do not express ER and express high levels of Cyr61, such as the MDA-MB-231 cells. Our results are in agreement with our knowledge that Cyr61 promotes tumor growth, and that tumor-promoting agents have a positive impact on cells that express low levels of Cyr61, such as the ER-positive breast cancer cells; however, these agents have no significant effect on cells that express high levels of Cyr61. Our findings suggest an association between increased Cyr61 expression and an aggressive phenotype of breast cancer cells.

Cyr61, a member of CCN family, is a tumor suppressor in non-small cell lung cancer

Cysteine-rich protein 61 (Cyr61) is a member of a family of growth factor-inducible immediate-early genes. It regulates cell adhesion, migration, proliferation, and differentiation and is involved in tumor growth. In our experiments, the role of Cyr61 in non-small cell lung cancer (NSCLC) was examined. Expression of Cyr61 mRNA was decreased markedly in four of five human lung tumor samples compared with their normal matched lung samples. NSCLC cell lines NCI-H520 and H460, which have no endogenous Cyr61, formed 60-90% fewer colonies after being transfected with a Cyr61 cDNA expression vector than cells transfected with the same amount of empty vector. After stable transfection of a Cyr61 cDNA expression vector, proliferation of both H520-Cyr61 and H460-Cyr61 sublines decreased remarkably compared with the cells stably transfected with empty vector. The addition of antibody against Cyr61 partially rescued the growth suppression of both H520-Cyr61 and H460-Cyr61 cells. Cell cycle analysis revealed that both H520-Cyr61 and H460-Cyr61 cells developed G(1) arrest, prominently up-regulated expression of p53 and p21(WAF1), and had decreased activity of cyclin-dependent kinase 2. The increase of pocket protein pRB2/p130 was also detected in these cells. Notably, both of the Cyr61-stably transfected lung cancer cell lines developed smaller tumors than those formed by the wild-type cells in nude mice. Taken together, we conclude that Cyr61 may play a role as a tumor suppressor in NSCLC.

The angiogenic factor Cyr61 activates a genetic program for wound healing in human skin fibroblasts

Cyr61 is a heparin-binding, extracellular matrix-associated protein of the CCN family, which also includes connective tissue growth factor, Nov, WISP-1, WISP-2, and WISP-3. Cyr61 is capable of multiple functions, including induction of angiogenesis in vivo. Purified Cyr61 mediates cell adhesion and induces adhesive signaling, stimulates cell migration, enhances cell proliferation, and promotes cell survival in both fibroblasts and endothelial cells. In this study, we have used cDNA array hybridization to identify genes regulated by Cyr61 in primary human skin fibroblasts. The Cyr61-regulated genes fall into several groups known to participate in processes important for cutaneous wound healing, including: 1) angiogenesis and lymphogenesis (VEGF-A and VEGF-C); 2) inflammation (interleukin-1beta); 3) extracellular matrix remodeling (MMP1, MMP3, TIMP1, uPA, and PAI-1); and 4) cell-matrix interactions (Col1alpha1, Col1alpha2, and integrins alpha(3) and alpha(5)). Cyr61-mediated gene expression requires heparin binding activity of Cyr61, cellular de novo transcription, and protein synthesis and is largely dependent on the activation of p42/p44 MAPKs. Cyr61 regulates gene expression not only in serum-free medium but also in fibroblasts cultured on various matrix proteins or in the presence of 10% serum. These effects of Cyr61 can be sustained for at least 5 days, consistent with the time course of wound healing in vivo. Interestingly, Cyr61 can interact with transforming growth factor-beta1 to regulate expression of specific genes in an antagonistic, additive, or synergistic manner. Furthermore, we show that the Cyr61 gene is highly induced in dermal fibroblasts of granulation tissue during cutaneous wound repair. Together, these results show that Cyr61 is inducibly expressed in granulation tissues after wounding and that Cyr61 activates a genetic program for wound repair in skin fibroblasts. We propose a model in which Cyr61 integrates its activities on endothelial cells, fibroblasts, and macrophages to regulate the processes of angiogenesis, inflammation, and matrix remodeling in the context of cutaneous wound healing.

Regulation of Cyr61 gene expression by mechanical stretch through multiple signaling pathways

The cysteine-rich protein 61 (Cyr61) is a signaling molecule with functions in cell migration, adhesion, and proliferation. This protein is encoded by an immediate early gene whose expression is mainly induced by serum growth factors. Here we show that Cyr61 mRNA levels increase sharply in response to cyclic mechanical stretch applied to cultured bladder smooth muscle cells. Stretch-induced changes of Cyr61 transcripts were transient and accompanied by an increase of the encoded protein that localized mainly to the cytoplasm and nucleus of the cells. With the use of pharmacological agents that interfere with known signaling pathways, we show that transduction mechanisms involving protein kinase C and phosphatidylinositol 3-kinase activation partly blocked stretch-induced Cyr61 gene expression. Selective inhibition of Rho kinase pathways altered this stretch effect as well. Meanwhile, using inhibitors of the actin cytoskeleton, we show that Cyr61 gene expression is sensitive to mechanisms that sense actin dynamics. These results establish the regulation of Cyr61 gene by mechanical stretch and provide clues to the key signaling molecules involved in this process.