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.     

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.     

The matrix protein CCN1 (CYR61) promotes proliferation, migration and tube formation of endothelial progenitor cells

Neovascularization and re-endothelialization relies on circulating endothelial progenitor cells (EPCs), but their recruitment and angiogenic roles are subjected to regulation by the vascular microenvironment, which remains largely unknown. The present study was designed to investigate the effects of mature ECs and matrix protein CCN1 on the properties of EPCs. In a coculture system, effects of ECs on proliferation, migration and participation in tube-like formation of EPCs were evaluated, and functional assays were employed to identify the exact role of CCN1 in EPCs vitality and function. We demonstrated that ECs, as an indispensable part of the cellular milieu, significantly promoted the proliferation, migration and tube formation activities of EPCs, and more importantly, CCN1 was potentially involved in such effects of ECs. Expression of CCN1 in EPCs was significantly increased by serum, VEGF, ECs-cocultivation and ECs conditioned medium. Moreover, Ad-CCN1-mediated overexpression of CCN1 directly enhanced migration and tube formation of EPCs, whereas silencing of endogenous CCN1 in EPCs inhibits cell functions. Furthermore, CCN1 induced the expressions of chemokines and growth factors, such as MCP-1 and VEGF, suggesting a complex interaction between those proangiogenic factors. Our data suggest that matrix protein CCN1 may play an important role in microenvironment-mediated biological properties of EPCs.     

Identification of a novel integrin alphavbeta3 binding site in CCN1 (CYR61) critical for pro-angiogenic activities in vascular endothelial cells

CCN1 (CYR61) is a matricellular inducer of angiogenesis essential for successful vascular development. Though devoid of the canonical RGD sequence motif recognized by some integrins, CCN1 binds to, and functions through integrin alphavbeta3 to promote pro-angiogenic activities in activated endothelial cells. In this study we identify a 20-residue sequence, V2 (NCKHQCTCIDGAVGCIPLCP), in domain II of CCN1 as a novel binding site for integrin alphavbeta3. Immobilized synthetic V2 peptide supports alphavbeta3-mediated cell adhesion; soluble V2 peptide inhibits endothelial cell adhesion to CCN1 and the homologous family members CCN2 (connective tissue growth factor, CTGF) or CCN3 (NOV) but not to collagen. These activities are obliterated by mutation of the aspartate residue in the V2 peptide to alanine. The corresponding D125A mutation in the context of the N-terminal half of CCN1 (domains I and II) greatly diminished direct solid phase binding to purified integrin alphavbeta3 and abolished alphavbeta3-mediated cell adhesion activity. Likewise, soluble full-length CCN1 with the D125A mutation is defective in binding purified alphavbeta3 and impaired in alphavbeta3-mediated pro-angiogenic activities in vascular endothelial cells, including stimulation of cell migration and enhancement of DNA synthesis. In contrast, immobilized full-length CCN1-D125A mutant binds alphavbeta3 and supports alphavbeta3-mediated cell adhesion similar to wild type CCN1. These results indicate that V2 is the primary alphavbeta3 binding site in soluble CCN1, whereas additional cryptic alphavbeta3 binding site(s) in the C-terminal half of CCN1 becomes exposed when the protein is immobilized. Together, these results identify a novel and functionally important binding site for integrin alphavbeta3 and provide a new approach for dissecting alphavbeta3-specific CCN1 functions both in cultured cells and in the organism.     

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.     

CCN1 (CYR61) and CCN3 (NOV) signaling drives human trophoblast cells into senescence and stimulates migration properties

ABSTRACT

During placental development, continuous invasion of trophoblasts into the maternal compartment depends on the support of proliferating extravillous trophoblasts (EVTs). Unlike tumor cells, EVTs escape from the cell cycle before invasion into the decidua and spiral arteries. This study focused on the regulation properties of glycosylated and non-glycosylated matricellular CCN1 and CCN3, primarily for proliferation control in the benign SGHPL-5 trophoblast cell line, which originates from the first-trimester placenta. Treating SGHPL-5 trophoblast cells with the glycosylated forms of recombinant CCN1 and CCN3 decreased cell proliferation by bringing about G0/G1 cell cycle arrest, which was accompanied by the upregulation of activated Notch-1 and its target gene p21. Interestingly, both CCN proteins increased senescence-associated β-galactosidase activity and the expression of the senescence marker p16. The migration capability of SGHPL-5 cells was mostly enhanced in response to CCN1 and CCN3, by the activation of FAK and Akt kinase but not by the activation of ERK1/2. In summary, both CCN proteins play a key role in regulating trophoblast cell differentiation by inducing senescence and enhancing migration properties. Reduced levels of CCN1 and CCN3, as found in early-onset preeclampsia, could contribute to a shift from invasive to proliferative EVTs and may explain their shallow invasion properties in this disease.     

Multiple signals required for cyclic AMP-responsive element binding protein (CREB) binding protein interaction induced by CD3/CD28 costimulation

The optimal activation of cAMP-responsive element binding protein (CREB), similar to the full activation of T lymphocytes, requires the stimulation of both CD3 and CD28. Using a reporter system to detect interaction of CREB and CREB-binding protein (CBP), in this study we found that CREB binds to CBP only by engagement of both CD3 and CD28. CD3/CD28-promoted CREB-CBP interaction was dependent on p38 mitogen-activated protein kinase (MAPK) and calcium/calmodulin-dependent protein kinase (CaMK) IV in addition to the previously identified extracellular signal-regulated kinase pathway. Extracellular signal-regulated kinase, CaMKIV, and p38 MAPK were also the kinases involved in CREB Ser(133) phosphorylation induced by CD3/CD28. A reconstitution experiment illustrated that optimum CREB-CBP interaction and CREB trans-activation were attained when these three kinase pathways were simultaneously activated in T cells. Our results demonstrate that coordinated activation of different kinases leads to full activation of CREB. Notably, CD28 ligation activated p38 MAPK and CaMKIV, the kinases stimulated by CD3 engagement, suggesting that CD28 acts by increasing the activation extent of p38 MAPK and CaMKIV. These results support the model of a minimum activation threshold for CREB-CBP interaction that can be reached only when both CD3 and CD28 are stimulated.     

The CCN1 (CYR61) protein promotes skin growth by enhancing epithelial‐mesenchymal transition during skin expansion

The skin expansion technique is widely used to induce skin growth for large‐scale skin deformity reconstruction. However, the capacity for skin expansion is limited and searching for ways to improve the expansion efficiency is a challenge. In this study, we aimed to explore the possible mechanism of skin expansion and to find a potential therapeutic target on promoting skin growth. We conducted weighted gene coexpression network analysis (WGCNA) of microarray data generated from rat skin expansion and found CCN1 (CYR61) to be the central hub gene related to epithelial‐mesenchymal transition (EMT). CCN1 up‐regulation was confirmed in human and rat expanded skin and also in mechanically stretched rat keratinocytes, together with acquired mesenchymal phenotype. After CCN1 stimulation on keratinocytes, cell proliferation was promoted and partial EMT was induced by activating β‐catenin pathway. Treatment of CCN1 protein could significantly increase the flap thickness, improve the blood supply and restore the structure in a rat model of skin expansion, whereas inhibition of CCN1 through shRNA interference could dramatically reduce the efficiency of skin expansion. Our findings demonstrate that CCN1 plays a crucial role in skin expansion and that CCN1 may serve as a potential therapeutic target to promote skin growth and improve the efficiency of skin expansion.     

Identification of a novel integrin alphaMbeta2 binding site in CCN1 (CYR61), a matricellular protein expressed in healing wounds and atherosclerotic lesions

CCN1 (cysteine-rich 61) and CCN2 (connective tissue growth factor) are growth factor-inducible immediate-early gene products found in atherosclerotic lesions, restenosed blood vessels, and healing cutaneous wounds. Both CCN proteins have been shown to support cell adhesion and induce cell migration through interaction with integrin receptors. Recently, we have identified integrin alphaMbeta2 as the major adhesion receptor mediating monocyte adhesion to CCN1 and CCN2 and have shown that the alphaMI domain binds specifically to both proteins. In the present study, we demonstrated that activated monocytes adhered to a synthetic peptide (CCN1-H2, SSVKKYRPKYCGS) derived from a conserved region within the CCN1 C-terminal domain, and this process was blocked by the anti-alphaM monoclonal antibody 2LPM19c. Consistently, a glutathione S-transferase (GST) fusion protein containing the alphaMI domain (GST-alphaMI) bound to immobilized CCN1-H2 as well as to the corresponding H2 sequence in CCN2 (CCN2-H2, TSVKTYRAKFCGV). By contrast, a scrambled CCN1-H2 peptide and an 18-residue peptide derived from an adjacent sequence of CCN1-H2 failed to support monocyte adhesion or alphaMI domain binding. To confirm that the CCN1-H2 sequence within the CCN1 protein mediates alphaMbeta2 interaction, we developed an anti-peptide antibody against CCN1-H2 and showed that it specifically blocked GST-alphaMI binding to intact CCN1. Collectively, these results identify the H2 sequence in CCN1 and CCN2 as a novel integrin alphaMbeta2 binding motif that bears no apparent homology to any alphaMbeta2 binding sequence reported to date.     

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.     

Transcriptional activation of the rat glucagon gene by the cyclic AMP-responsive element in pancreatic islet cells.

The 5'-flanking region of the rat glucagon gene contains, from nucleotides -291 to -298, a sequence (TGA CGTCA) which mediates cyclic AMP (cAMP) responsiveness in several genes (cAMP-responsive element [CRE]). However, because of nonpermissive bases surrounding the CRE octamer, the glucagon CRE does not confer cAMP responsiveness to an inert heterologous promoter in placental JEG cells that do not express the glucagon gene. This report describes transient transfection experiments with glucagon-reporter fusion genes that show that glucagon gene expression is activated by cAMP-dependent protein kinase A in a glucagon-expressing pancreatic islet cell line. This activation is mediated through the glucagon CRE.     

Fas-Mediated Apoptosis Is Regulated by the Extracellular Matrix Protein CCN1 (CYR61) In Vitro and In Vivo

Although Fas ligand (FasL) is primarily expressed by lymphoid cells, its receptor Fas (CD95/Apo-1) is broadly expressed in numerous nonlymphoid tissues and can mediate apoptosis of parenchymal cells upon injury and infiltration of inflammatory cells. Here we show that CCN1 (CYR61) and CCN2 (CTGF), matricellular proteins upregulated at sites of inflammation and wound repair, synergize with FasL to induce apoptosis by elevating cellular levels of reactive oxygen species (ROS). CCN1 acts through engagement of integrin α₆β₁ and cell surface heparan sulfate proteoglycans, leading to ROS-dependent hyperactivation of p38 mitogen-activated protein kinase in the presence of FasL to enhance mitochondrial cytochrome c release. We show that CCN1 activates neutral sphingomyelinase, which functions as a key source of CCN1-induced ROS critical for synergism with FasL. Furthermore, Fas-dependent hepatic apoptosis induced by an agonistic monoclonal anti-Fas antibody or intragastric administration of alcohol is severely blunted in knock-in mice expressing an apoptosis-defective Ccn1 allele. These results demonstrate that CCN1 is a physiologic regulator of Fas-mediated apoptosis and that the extracellular matrix microenvironment can modulate Fas-dependent apoptosis through CCN1 expression.Cell adhesion to several abundant extracellular matrix (ECM) proteins via engagement of integrin receptors is known to induce potent prosurvival signals, whereas detachment from the ECM triggers many cell types to undergo anoikis, a form of apoptotic cell death (13). This regulation of cell survival through integrin-mediated cell adhesion plays a critical role in controlling homeostasis and the integrity of tissue architecture, whereas unligated or inappropriately ligated integrins may elicit apoptotic signals (12). However, during embryogenesis, inflammation, tissue remodeling, and wound repair, death-inducing factors can provoke programmed or apoptotic death in normal cells without requiring their detachment from the ECM (4).Fas (CD95/APO-1) is a member of the tumor necrosis factor (TNF) receptor family of cell surface death receptors that mediates apoptotic signals upon binding to its specific ligand, FasL. Ligation of Fas to FasL or its agonistic antibodies results in receptor clustering, recruitment of the adaptor protein FADD, and activation of the proteolytic caspase cascade (19, 50). Whereas FasL is primarily expressed in activated T lymphocytes, natural killer cells, and tissues of immune privilege, Fas is broadly expressed in most lymphoid and nonlymphoid tissues (50). Fas-mediated apoptosis is critical for the regulation of the immune response, including deletion of activated T and B lymphocytes, cell death-inducing activity of cytotoxic T cells, and removal of infiltrating lymphocytes in immune-privileged tissues (19, 50). Fas also plays an important role in parenchymal cell apoptosis in many organs during tissue injury and upon inflammatory infiltration of lymphocytes (7, 20, 38, 42, 46). Consistent with the notion that cell adhesion promotes cell survival, integrin-matrix interactions inhibit Fas-dependent apoptosis in a variety of cell types (22, 32). Thus, optimal apoptotic responses to Fas/FasL signaling in adherent parenchymal cells must override the cytoprotective effects of integrin-mediated cell adhesion. In these instances, dynamic changes in the ECM induced by inflammation or injury repair may establish conditions that are permissive of, or conducive to, the apoptotic responses to FasL.Recent studies have described the emergence of ECM proteins that can induce or promote apoptosis (49, 60, 65). Among them are members of the CCN family (9), which are secreted cysteine-rich proteins that serve regulatory rather than structural roles in the ECM and are therefore considered matricellular proteins (6). CCN1 (CYR61) and CCN2 (CTGF) support cell adhesion, stimulate cell migration, induce angiogenesis, and promote chondrogenic differentiation, exerting their functions primarily through direct binding to integrin receptors. CCN1 and CCN2 promote the survival of endothelial cells through integrin α_vβ₃ but induce apoptosis in p21-deficient fibroblasts through α₆β₁ via a caspase-8-independent mechanism (3, 40, 60). CCN1 and CCN2 are also critical for embryonic development, as Ccn1-null mice die during midgestation due to cardiovascular abnormalities and Ccn2-deficient mice perish perinatally as a consequence of severe skeletal malformations (29, 47, 48). In the adult, CCN proteins are highly expressed at sites of inflammation, injury repair, and tissue remodeling and are implicated in diseases where inflammation plays a role, including fibrosis, atherosclerosis, arthritis, and cancer (9). Furthermore, the presence of CCN1 in the ECM enables TNF-α to induce apoptotic death in normal cells without inhibition of NF-κB signaling or de novo protein synthesis, conditions thought to be necessary for TNF-α to be cytotoxic (10).Here we show that CCN1 and CCN2 can synergize with FasL and significantly enhance FasL-induced apoptosis in fibroblasts. Mechanistically, CCN1 engages integrin α₆β₁ and cell surface heparan sulfate proteoglycans (HSPGs), leading to the reactive oxygen species (ROS)-dependent hyperactivation of p38 mitogen-activated protein kinase (MAPK) in the presence of FasL, which greatly enhances mitochondrial cytochrome c release and apoptosis. We show that CCN1 is a novel activator of neutral sphingomyelinase (nSMase), which is an essential contributor to CCN1-induced ROS. Further, Fas-dependent hepatic cell death is greatly diminished in knock-in mice expressing an apoptosis-defective mutant of CCN1 that is unable to bind α₆β₁-HSPGs. Together, these results show that CCN1 is a physiologic regulator of Fas-mediated apoptosis and indicate that Fas-dependent cell death at sites of inflammation and injury repair may be controlled by the matrix microenvironment through CCN1 expression.     

Cysteine-rich protein 61 (CCN1) and connective tissue growth factor (CCN2) at the crosshairs of ocular neovascular and fibrovascular disease therapy

Abstract

The vasculature forms a highly branched network investing every organ of vertebrate organisms. The retinal circulation, in particular, is supported by a central retinal artery branching into superficial arteries, which dive into the retina to form a dense network of capillaries in the deeper retinal layers. The function of the retina is highly dependent on the integrity and proper functioning of its vascular network and numerous ocular diseases including diabetic retinopathy, age-related macular degeneration and retinopathy of prematurity are caused by vascular abnormalities culminating in total and sometimes irreversible loss of vision. CCN1 and CCN2 are inducible extracellular matrix (ECM) proteins which play a major role in normal and aberrant formation of blood vessels as their expression is associated with developmental and pathological angiogenesis. Both CCN1 and CCN2 achieve disparate cell-type and context-dependent activities through modulation of the angiogenic and synthetic phenotype of vascular and mesenchymal cells respectively. At the molecular level, CCN1 and CCN2 may control capillary growth and vascular cell differentiation by altering the composition or function of the constitutive ECM proteins, potentiating or interfering with the activity of various ligands and/or their receptors, physically interfering with the ECM-cell surface interconnections, and/or reprogramming gene expression driving cells toward new phenotypes. As such, these proteins emerged as important prognostic markers and potential therapeutic targets in neovascular and fibrovascular diseases of the eye. The purpose of this review is to highlight our current knowledge and understanding of the most recent data linking CCN1 and CCN2 signaling to ocular neovascularization bolstering the potential value of targeting these proteins in a therapeutic context.     

Targeted mutagenesis of the angiogenic protein CCN1 (CYR61). Selective inactivation of integrin alpha6beta1-heparan sulfate proteoglycan coreceptor-mediated cellular functions

The matricellular protein CCN1 (CYR61) regulates multiple cellular processes and plays essential roles in embryonic vascular development. A ligand of several integrin receptors, CCN1 acts through integrin alpha6beta1 and heparan sulfate proteoglycans (HSPGs) to promote specific functions in fibroblasts, smooth muscle cells, and endothelial cells. We have previously identified a novel alpha6beta1 binding site, T1, in domain III of CCN1. Here we uncover two novel 16-residue sequences, H1 and H2, in domain IV that can support alpha6beta1- and HSPGs-dependent cell adhesion, suggesting that these sequences contain closely juxtaposed or overlapping sites for interaction with alpha6beta1 and HSPGs. Furthermore, fibroblast adhesion to the H1 and H2 peptides is sufficient to induce prolonged MAPK activation, whereas adhesion to T1 induces transient MAPK activation. To dissect the roles of these sites in CCN1 function, we have created mutants disrupted in T1, H1, and H2 or in all three sites in the context of full-length CCN1. We show that the T1 and H1/H2 sites are functionally non-equivalent, and disruption of these sites differentially affected cell adhesion, migration, mitogen-activated protein kinase activation, and regulation of gene expression. Disruption of all three sites completely abolished alpha6beta1-HSPG-mediated cellular activities. All mutants disrupting T1, H1, and H2 fully retain alphavbeta3-mediated pro-angiogenic activities, indicating that these mutants are biologically active and are defective only in alpha6beta1-HSPG-mediated functions. Together, these findings identify and dissect the differential roles of the three sites (T1, H1, H2) required for alpha6beta1-HSPG-dependent CCN1 activities and provide a strategy to investigate these alpha6beta1-HSPG-specific activities in vivo.     

Interaction of early growth response protein 1 (Egr-1), specificity protein 1 (Sp1), and cyclic adenosine 3'5'-monophosphate response element binding protein (CREB) at a proximal response element is critical for gastrin-dependent activation of the chromogranin A promoter

Recently, binding of specific protein 1 (Sp1) and cAMP response element binding protein (CREB) to a GC-rich element at -92/-62 has been identified as a critical step in gastrin-dependent regulation of the chromogranin A (CgA) gene in gastric epithelial cells. Here we demonstrate that binding of early growth response protein 1 (Egr-1) to the distal part of the -92/-62 site is also required for gastrin-dependent CgA transactivation. Gastrin elevated cellular and nuclear Egr-1 levels in a time-dependent manner and also increased Egr-1 binding to the CgA -92/-73 region. Disruption of this site reduced gastrin responsiveness without influencing basal promoter activity, while loss of Sp1 and/or CREB binding sites diminished basal and gastrin-stimulated CgA promoter activity. Ectopic Egr-1 overexpression potently stimulated the CgA promoter, whereas coexpression of Egr-1 with Sp1 and/or CREB resulted in additive effects. Functional analysis of Sp1-, Egr-1-, or CREB-specific promoter mutations in transfection studies confirmed the tripartite organization of the CgA -92/-62 element. Signaling studies revealed that MAPK kinase 1 (MEK1)/ERK1/2 cascades are critical for gastrin-dependent Egr-1 protein accumulation as well as Egr-1 binding to the CgA promoter. Our studies for the first time identify Egr-1 as a nuclear target of gastrin and show that functional interplay of Egr-1, Sp1, and CREB is indispensable for gastrin-dependent CgA transactivation in gastric epithelial cells.     

Cysteine-rich protein 61 (CCN1) mediates replicative senescence-associated aberrant collagen homeostasis in human skin fibroblasts

Dermal fibroblasts produce a collagen-rich extracellular matrix, which confers mechanical strength and resiliency to human skin. During aging, collagen production is reduced and collagen fragmentation is increased, which is initiated by matrix metalloproteinase-1 (MMP-1). This aberrant collagen homeostasis results in net collagen deficiency, which impairs the structural integrity and function of skin. Cysteine-rich protein 61 (CCN1), a member of the CCN family, negatively regulates collagen homeostasis, in primary human skin dermal fibroblasts. As replicative senescence is a form of cellular aging, we have utilized replicative senescent dermal fibroblasts to further investigate the connection between elevated CCN1 and aberrant collagen homeostasis. CCN1 mRNA and protein levels were significantly elevated in replicative senescent dermal fibroblasts. Replicative senescent dermal fibroblasts also expressed significantly reduced levels of type I procollagen and increased levels of MMP-1. Knockdown of elevated CCN1 in senescent dermal fibroblasts partially normalized both type I procollagen and MMP-1 expression. These data further support a key role of CCN1 in regulation of collagen homeostasis. Elevated expression of CCN1 substantially increased collagen lattice contraction and fragmentation caused by replicative senescent dermal fibroblasts. Atomic force microscopy (AFM) further revealed collagen fibril fragmentation and disorganization were largely prevented by knockdown of CCN1 in replicative senescent dermal fibroblasts, suggesting CCN1 mediates MMP-1-induced alterations of collagen fibrils by replicative senescent dermal fibroblasts. Given the ability of CCN1 to regulate both production and degradation of type I collagen, it is likely that elevated-CCN1 functions as an important mediator of collagen loss, which is observed in aged human skin.