Vitronectin is a multifunctional glycoprotein present in blood and in the extracellular matrix. It binds glycosaminoglycans, collagen, plasminogen and the urokinase-receptor, and also stabilizes the inhibitory conformation of plasminogen activation inhibitor-1. By its localization in the extracellular matrix and its binding to plasminogen activation inhibitor-1, vitronectin can potentially regulate the proteolytic degradation of this matrix. In addition, vitronectin binds to complement, to heparin and to thrombin-antithrombin III complexes, implicating its participation in the immune response and in the regulation of clot formation. The biological functions of vitronectin can be modulated by proteolytic enzymes, and by exo- and ecto-protein kinases present in blood. Vitronectin contains an RGD sequence, through which it binds to the integrin receptor alpha v beta 3, and is involved in the cell attachment, spreading and migration. Antibodies against alpha v beta 3 or synthetic peptides containing an RGD sequence are now being tested as therapeutic agents in the treatment of human cancers, bone diseases (e.g. osteoporosis) and in pathological disorders which involve angiogenesis.

The amino acid sequences of all known cGMP-binding phosphodiesterases (PDEs) contain internally homologous repeats (a and b) that are 80 -90 residues in length and are arranged in tandem within the putative cGMPbinding domains. In the bovine lung cGMP-binding, cGMP-specific PDE (cGB-PDE or PDE5A), these repeats span residues 228 -311 (a) and 410 -500 (b). An aspartic acid (residue 289 or 478) that is invariant in repeats a and b of all known cGMP-binding PDEs was changed to alanine by site-directed mutagenesis of cGB-PDE, and wild type (WT) and mutant cGB-PDEs were expressed in COS-7 cells. Purified bovine lung cGB-PDE (native) and WT cGB-PDE displayed identical cGMP-binding kinetics, with ϳ1.8 M cGMP required for half-maximal saturation. The D289A mutant showed decreased affinity for cGMP (K d > 10 M) and the D478A mutant showed increased affinity for cGMP (K d Ϸ 0.5 M) as compared to WT and native cGB-PDE. WT and native cGB-PDE displayed an identical curvilinear profile of cGMP dissociation which was consistent with the presence of distinct slowly dissociating (k off ‫؍‬ 0.26 h ؊1 ) and rapidly dissociating (k off ‫؍‬ 1.00 h ؊1 ) sites of cGMP binding. In contrast, the D289A mutant displayed a single k off ‫؍‬ 1.24 h ؊1 , which was similar to the calculated k off for the fast site of WT and native cGB-PDE, and the D478A mutant displayed a single k off ‫؍‬ 0.29 h ؊1, which was similar to that calculated for the slow site of WT and native cGB-PDE. These results were consistent with the loss of a slow cGMP-binding site in repeat a of the D289A mutant cGB-PDE, and the loss of a fast site in repeat b of the D478A mutant, suggesting that cGB-PDE possesses two distinct cGMP-binding sites located at repeats a and b, with the invariant aspartic acid being crucial for interaction with cGMP at each site. Cyclic nucleotide phosphodiesterases (PDEs)1 constitute a complex family of enzymes which catalyze the hydrolysis of 3Ј:5Ј-cyclic nucleotides to the corresponding nucleoside 5Ј-monophosphates. The multiple PDEs differ in their substrate specificities, sensitivities to inhibitors, modes of regulation, and tissue distributions. Most PDEs are chimeric multidomain proteins, possessing distinct catalytic and regulatory domains (1). A 250-amino acid segment of sequence, which is conserved among all mammalian PDEs and is located in the more carboxyl-terminal portions of the PDE molecules, contains the catalytic site of these enzymes (1-4). Domains of the PDEs which interact with allosteric/regulatory factors are thought to be located within the more amino-terminal regions (1, 5, 6).The cGMP-binding PDEs comprise a heterogeneous subgroup of PDEs, all of which exhibit allosteric cGMP-binding sites that are distinct from the sites of cyclic nucleotide hydrolysis. This group consists of at least three classes of PDEs: the cGMP-stimulated PDEs (cGS-PDEs, or PDE2s 2 ) (7), the photoreceptor PDEs (rod outer segment PDE (ROS-PDE; PDE6A/B) (8) and cone PDE (PDE6C) (9)), and the cGMP-binding, cGMPspecific PDE (cGB-PDE; PDE5A) (10). The s...

We report on a short host defense-like peptide that targets and arrests the growth of aggressive and hormone-resistant primary human prostate and breast tumors and prevents their experimental and spontaneous metastases, respectively, when systemically inoculated to immuodeficient mice. These effects are correlated with increased necrosis of the tumor cells and a significant decrease in the overall tumor microvessel density, as well as newly formed capillary tubes and prostate-specific antigen secretion (in prostate tumors). Growth inhibition of orthotopic tumors derived from stably transfected highly fluorescent human breast cancer cells and prevention of their naturally occurring metastases were visualized in real time by using noninvasive whole-body optical imaging. The exclusive selectivity of the peptide towards cancer derives from its specific binding to surface phosphatidylserine and the killing of the cancer cells via cytoplasmic membrane depolarization. These data indicate that membrane disruption can provide a therapeutic means of inhibiting tumor growth and preventing metastases of various cancers. (Cancer Res 2006; 66(10): 5371-8)

Using a bovine 61-kDa (PDE1A2) calmodulin-stimulated phosphodiesterase (CaM-PDE) cDNA and a bovine lung 59-kDa (PDE1A1) CaM-PDE cDNA reported here, we have identified two new regions within the primary structure of these two related isozymes that are important for regulation by Ca 2؉ /CaM. PDE1A1 is identical to the PDE1A2 isozyme except for the amino-terminal 18 residues. In agreement with earlier studies, the CaM concentration required for half-maximal activation (K CaM ) of recombinant PDE1A1 (0.3 nM) was Ϸ10-fold less than the K CaM for recombinant PDE1A2 (4 nM). A series of deletion mutations of the PDE1A2 cDNA removing nucleotide sequence encoding the first 46 -106 aminoterminal residues were constructed and expressed using the baculovirus system. Deletion of the amino acids encompassing a previously identified, putative CaMbinding domain (residues 4 -46) produced a polypeptide that was still activated 3-fold by CaM (K CaM Ϸ 3 nM). However, complete CaM-independent activation occurred when residues 4 -98 were deleted. To determine the location of the additional CaM-binding domain(s), the inhibitory potency of seven overlapping, synthetic peptides spanning amino acids 76 -149 of PDE1A2 was tested using the CaM-activated enzyme. One peptide spanning amino acids 114 -137 of PDE1A2 appeared to be the most potent inhibitor of CaM-stimulated activity. These results reveal the existence of a CaM-binding domain located approximately 90 residues carboxyl-terminal to the putative CaM-binding domains previously identified within the PDE1A1 and PDE1A2 isozymes. Moreover, a discrete segment important for holding these CaM-PDEs in a less active state at low Ca 2؉ concentrations is located between the two CaM-binding domains.Calmodulin-stimulated cyclic nucleotide phosphodiesterases (CaM-PDEs) 1 constitute a genetically diverse class of cAMP and cGMP hydrolyzing activities that are activated by calcium and calmodulin (1). Several different CaM-PDE activities have been identified (2). These CaM-PDE isozymes are distributed among discrete cell types in various tissues and have varying substrate specificity, specific activities, and activation constants (K CaM ) for CaM (2, 3). In cells that express CaM-PDEs, hormones that increase cytosolic Ca 2ϩ would be predicted to activate this isozyme, thereby decreasing cyclic nucleotide accumulation in response to hormones that stimulate cAMP or cGMP synthesis.In addition to Ca 2ϩ /CaM, certain CaM-PDEs may be subject to a secondary form of regulation via phosphorylation. In vitro, the 59-kDa (PDE1A1) and 61-kDa (PDE1A2) CaM-PDEs 2 are phosphorylated by cAMP-dependent protein kinase (4, 5), while the autophosphorylated form of CaM-dependent protein kinase II catalyzes the phosphorylation of the 63-kDa (PDE1B1) CaM-PDE (6). Phosphorylation increases the K CaM , effectively rendering these isozymes less sensitive to activation by Ca 2ϩ (7,8). In vivo, CaM-PDE phosphorylation would likely result in potentiation of cAMP or cGMP accumulation in response to hormonal stimuli involving coin...

No abstract

Amplified HER2, which encodes a member of the epidermal growth factor receptor (EGFR) family, is a target of effective therapies against breast cancer. In search for similarly targetable genomic aberrations, we identified copy number gains in SYNJ2, which encodes the 5'-inositol lipid phosphatase synaptojanin 2, as well as overexpression in a small fraction of human breast tumors. Copy gain and overexpression correlated with shorter patient survival and a low abundance of the tumor suppressor microRNA miR-31. SYNJ2 promoted cell migration and invasion in culture and lung metastasis of breast tumor xenografts in mice. Knocking down SYNJ2 impaired the endocytic recycling of EGFR and the formation of cellular lamellipodia and invadopodia. Screening compound libraries identified SYNJ2-specific inhibitors that prevented cell migration but did not affect the related neural protein SYNJ1, suggesting that SYNJ2 is a potentially druggable target to block cancer cell migration.

Cancer cells utilize glucose as their main energy source and convert it to lactate at high rates, even in the presence of high oxygen concentrations. 1 Previous studies have indicated that the enhanced rate of glucose uptake in tumors might be related to an overexpression of the facilitated glucose transporter proteins. 2,3 Further studies of inducing malignant transformation of fibroblast cells by transfection with ras or src demonstrated upregulation of the glucose transporters as well. 4,5 More recently transformation of cells by c-myc transfection of rat fibroblasts showed specific induction of the glucose transporter 1 (GLUT1) expression. 6 Enhanced glycolysis and high expression of the glucose transporters were specifically identified in human breast cancer cells. [7][8][9][10][11] In addition, the expression of GLUT1 was found to be a characteristic feature in breast cancer biopsies, with a positive correlation between this expression and tumor grade, extent of proliferation and invasiveness. [12][13][14][15][16] Recently, Kang et al. 17 investigated the clinical significance of GLUT1 expression in human breast carcinoma and found a significant correlation between GLUT1 expression and estrogen and progesterone receptor status. These results are in accord with studies of human breast cancer cells in vitro, where induction of cellular differentiation of human breast cancer cells resulted in decreased expression of protein GLUT1. 9 The above findings emphasize that malignant transformation is involved in the deregulation of the expression of the glucose transporters and consequently the augmentation of glucose metabolism and glycolysis.A large number of breast tumors express receptors for estrogen, which regulates various cellular activities by modulating metabolism in the course of tumor growth and progression. 18,19 The estrogen receptors (ER ␣ and ␤), which are ligand-dependent transcription factors, 20 play a key role in the development and progression of breast cancer, as well as in the treatment of breast cancer patients. 21 Tamoxifen, the leading antiestrogenic drug, has been proven to be effective in improving overall survival in both pre-and postmenopausal women. 22 Furthermore, tamoxifen also has been shown to reduce cancer incidence and prevent new tumor formation and growth. 23 Estrogen binding to its receptor induces critical metabolic and physiologic activities via activating various ER-responsive genes. Specifically, estrogen was shown to stimulate glucose metabolism and glycolysis in various target organs, including the uterus-the classic estrogen target organ. 24,25 Furthermore, in the uterus and primate cerebral cortex, it was found that estrogen regulation of glycolysis is mediated by altering the expression levels of GLUT1. 26,27 In breast cancer, kinetic studies of perfused cells in vitro have demonstrated induction of glycolysis by estrogen and its inhibition by tamoxifen. 7,8 The prevalent role of estrogen in breast cancer progression and the need for developing objective surrogate ma...

Metastatic spread to regional lymph nodes is one of the earliest events of tumor cell dissemination and presents a most significant prognostic factor for predicting survival of cancer patients. Real-time in vivo imaging of the spread of tumor cells through the lymphatic system can enhance our understanding of the metastatic process. Herein, we describe the use of in vivo fluorescence microscopy imaging to monitor the progression of lymph node metastasis as well as the course of spontaneous metastasis through the lymphatic system of orthotopic MDA-MB-231 human breast cancer tumors in severe combined immunodeficient mice. High-resolution noninvasive visualization of metastasizing cancer cells in the inguinal lymph nodes was achieved using cells expressing high levels of red fluorescent protein. Sequential imaging of these lymph nodes revealed the initial invasion of the tumor cells through the lymphatic system into the subcapsular sinuses followed by intrusion into the parenchyma of the nodes. FITCdextran injected i.d. in the tumor area enabled simultaneous tracking of lymphatic vessels, labeled in green, and disseminated red cancer cells within these vessels. Fast snapshots of spontaneously metastasizing cells in the lymphatic vessels monitored the movement of a few tumor cells and the development of clumps clustered at lymphatic vessel junctions. Quantification of high interstitial fluid pressure (IFP) in the tumors and fast drainage rates of the FITC-dextran into the peritumoral lymphatic vessels suggested an IFP-induced intravasation into the lymphatic system. This work presents unprecedented live fluorescence images that may help to clarify the steps occurring in the course of spontaneous lymphogenic metastasis. (Cancer Res 2006; 66(16): 8037-41)