The molecular structure of corticotropin-induced secreted protein, a novel member of the thrombospondin family

Thrombospondin-2 acts as a critical regulator of cartilage regeneration: A review

The degeneration of articular cartilage tissue is the most common cause of articular cartilage diseases such as osteoarthritis. There are limitations in chondrocyte self-renewal and conventional treatments. During cartilage regeneration and repair, growth factors are typically used to induce cartilage differentiation in stem cells. The role of thrombospondin-2 in cartilage formation has received much attention in recent years. This paper reviews the role of thrombospondin-2 in cartilage regeneration and the important role it plays in protecting cartilage from damage caused by inflammation or trauma and in the regenerative repair of cartilage by binding to different receptors and activating different intracellular signaling pathways. These studies provide new ideas for cartilage repair in clinical settings.

A comparison between the equine and bovine hypothalamus-pituitary-adrenocortical axis

In this review, we address the function of the hypothalamus-pituitary-adrenocortical (HPA) axis with special emphasis on the comparison between the bovine and equine species. The pars intermedia of the pituitary gland is particularly well developed in horses and cattle. However, its function is not well appreciated in cattle yet. The Wulzen's cone of the adenohypophysis is a special feature of ruminants. Total basal cortisol concentration is much higher in horses than that in cows with similar free cortisol fractions. Corticotropin-releasing factor (CRF) concentrations in equine pituitary venous blood are lower compared with other species, whereas plasma ACTH concentrations in cows are higher than those in horses. A CRF challenge test induced a more pronounced cortisol response in horses compared with cattle, whereas regarding ACTH challenge testing, the opposite seems true. Based on data from literature, the bovine species is characterized by relatively high basal blood CRF and ACTH and low cortisol and glucose concentrations. Obviously, further lowering of blood cortisol in cattle is easily prevented by the high sensitivity to ACTH, and as a consequence, subsequent increased gluconeogenesis prevents imminent hypoglycemia. Hypoglycemia is less likely in horses given their high muscle glycogen content and their relatively high cortisol concentration. When assessing HPA axis reactivity, response patterns to exogenous ACTH or CRH might be used as a reliable indicator of animal welfare status in cows and horses, respectively, although it is emphasized that considerable caution should be exercised in using measures of HPA activity solely to assess animal welfare.

Differential zonal expression and adrenocorticotropin regulation of secreted protein acidic and rich in cysteine (SPARC), a matricellular protein, in the midgestation human fetal adrenal gland: implications for adrenal development

CONTEXT

Matricellular proteins are a group of secreted, multifunctional extracellular matrix glycoproteins that includes thrombospondins (TSPs), tenascin-C, and secreted protein acidic and rich in cysteine (SPARC). They may be implicated in the dynamic developmental processes of the human fetal adrenal (HFA) in which the outer, definitive zone (DZ) cells are postulated to proliferate, migrate centripetally, differentiate, and populate the inner, steroidogenic fetal zone (FZ).

OBJECTIVE

The objective of the study was to identify a matricellular molecule that likely plays a major role in HFA development.

DESIGN

Studies involved RNA, cryosections, and cell cultures from 14- to 23-wk HFAs and human adult adrenal RNA.

MAIN OUTCOME MEASURES

Measures included transcripts encoding matricellular proteins, using real-time quantitative RT-PCR; SPARC localization by immunostaining; and ACTH regulation of SPARC expression and secretion by quantitative RT-PCR and Western blot.

RESULTS

SPARC HFA mRNA was 100-, 700-, and 300-fold higher than TSP-1, TSP-2, and tenascin-C mRNA, respectively. HFA SPARC mRNA was 3-fold higher than adult adrenals (P < 0.005), comparable with levels in adult brain (positive control), whereas mRNAs encoding TSP-1 and TSP-2 were lower in fetal than adult adrenals. SPARC immunoreactivity was detected exclusively in the FZ, not DZ. ACTH, a key regulator of HFA growth and function, increased SPARC mRNA (by 1.7-fold at 1 nm, 48 h, P < 0.05) in isolated FZ cells but not DZ cells. ACTH up-regulation of SPARC protein was also detected in FZ cell lysates and culture medium.

CONCLUSIONS

Results suggest a possible role for SPARC in development of functional and/or structural zonation of the HFA.

An N-Terminal 80 kDa Recombinant Fragment of Human Thrombospondin-2 Inhibits Vascular Endothelial Growth Factor Induced Endothelial Cell Migration In Vitro and Tumor Growth and Angiogenesis In Vivo

We have previously shown that stable overexpression of the thrombospondin-2 (TSP-2) gene inhibited the tumor growth and angiogenesis of human squamous cell carcinoma xenotransplants. To investigate the potential antitumoral efficacy of systemic TSP-2 therapy, we expressed a recombinant 80 kDa fragment of human TSP-2 (TSP-2/NTF), encompassing the N-terminal globular region through the three type 1 repeats, in human kidney 293 EBNA cells, using a modified pCEP4 expression vector. Daily intraperitoneal injections of TSP-2/NTF resulted in a significant inhibition of the growth of human A431 squamous cell carcinomas in vivo and in reduced tumor vascularization. To further investigate possible mechanisms of the antiangiogenic activity of TSP-2/NTF, several in vitro angiogenesis assays were performed in human dermal microvascular endothelial cells. TSP-2/NTF inhibited vascular endothelial growth factor induced migration of human dermal microvascular endothelial cells and inhibited tube formation on Matrigel in vitro. TSP-2/NTF also inhibited vascular endothelial growth factor induced angiogenesis in an in vivo Matrigel assay. Moreover, TSP-2/NTF potently induced human dermal microvascular endothelial cell apoptosis in vitro but did not affect A431 tumor cell proliferation or apoptosis. These findings identify TSP-2/NTF as a potent systemic inhibitor of tumor growth and angiogenesis, acting by direct inhibition of several endothelial cell functions involved in neovascularization.

Thrombospondin 2, a matricellular protein with diverse functions

Thrombospondin (TSP) 2 is a close relative of TSP1 but differs in its temporal and spatial distribution in the mouse. This difference in expression undoubtedly reflects the marked disparity in the DNA sequences of the promoters in the genes encoding the two proteins. The synthesis of TSP2 occurs primarily in connective tissues of the developing and growing mouse. In the adult animal the protein is again produced in response to tissue injury and in association with the growth of tumors. Despite the abnormalities in collagen fibrillogenesis, fragility of skin, and laxity of tendons and ligaments observed in the TSP2-null mouse, TSP2 does not appear to contribute directly to the structural integrity of connective tissue elements. Instead, emerging evidence supports a mode of action of TSP2 'at a distance', i.e. by modulating the activity and bioavailability of proteases and growth factors in the pericellular environment and, very likely, by interaction with cell-surface receptors. Thus, TSP2 qualifies as a matricellular protein, as defined in the introduction to this minireview series. The phenotype of TSP2-null mice has been very helpful in providing clues to the functions of TSP2. In addition to histological and functional abnormalities in connective tissues, these mice display an increased vascularity of the dermis and subdermal tissues, increased endosteal bone growth, a bleeding defect, and a marked adhesive defect of dermal fibroblasts. Our laboratory has established that TSP2 binds matrix metalloproteinase 2 (MMP2) and that the adhesive defect in TSP2-null fibroblasts results from increased MMP2 activity. The investigation of the basis for the other defects in the TSP2-null mouse is likely to yield equally interesting results.

The thrombospondin type 1 repeat (TSR) superfamily: diverse proteins with related roles in neuronal development

The thrombospondins are a family of proteins found widely in the embryonic extracellular matrix. Like most matrix proteins, thrombospondins are modular and contain a series of repeated domains arrayed between globular amino and carboxyl terminal domains. In recent years, other proteins that share thrombospondin type 1 repeats, or TSRs, have been identified. These include the F-spondin gene family, the members of the semaphorin 5 family, UNC-5, SCO-spondin, and others. Most of these are expressed in the developing nervous system, and many have expression patterns and in vitro properties that suggest potential roles in the guidance of cell and growth cone migration. Both cell- and matrix-binding motifs have been identified in the TSRs of thrombospondin-1, so it has been hypothesized that the properties of these diverse proteins may also depend on the presence of these repeats. Here, we review the cell biology of the TSR module, the extensive literature regarding the distribution and functions of thrombospondins and other TSR superfamily proteins, and evaluate their possible roles during the development of the nervous system.

Different immunohistochemical patterns of TGF-beta1 expression in benign and malignant adrenocortical tumours

OBJECTIVE

Transforming growth-factor beta1 (TGF-beta1) influences a number of specific functions of adrenocortical cells in several animal species. The aim of our study was to evaluate by immunohistochemical analysis the presence and distribution of TGF-beta1 in normal adrenal tissue and in different adrenal tumours.

PATIENTS

We analysed 8 functioning (5 adenomas and 3 carcinomas) and 15 non functioning (6 adenomas and 9 carcinomas) adrenal tumours and 6 normal adrenal glands.

RESULTS

In normal adrenal glands, the glomerulosa and the reticularis zones displayed diffuse cytoplasmic staining, while the fasciculata zone was almost completely negative. Functioning adenomas displayed cytoplasmic staining restricted to compact cells while in nonfunctioning adenomas, prevalently composed by clear cells, no staining was observed. Overall, adrenal carcinomas were characterized by the lack of cytoplasmic positivity and by sporadic positive cells around vessels both in functioning and in nonfunctioning tumours.

CONCLUSIONS

TGF-beta1 expression is associated with active steroid secretion in normal adrenal tissue, as well as in benign cortical adenomas, while this relationship is lost in primary adrenal malignancies. These data provide indirect evidence for a regulatory role played by TGF-beta1 on steroid secretory pathways.

Bovine thrombospondin-2: complete complementary deoxyribonucleic acid sequence and immunolocalization in the external zones of the adrenal cortex

Given the variety of biological functions in the adrenal cortex that are controlled by ACTH, we hypothesized that some extracellular proteins act as biological relays for this systemic hormone. One candidate protein [corticotropin-induced secreted protein (CISP)] was purified from the conditioned medium of bovine adrenocortical cells on the basis of a 5- to 14-fold increase in its synthesis after the addition of ACTH. We report here the cloning of overlapping complementary DNAs that span the sequence encoding the full-length protein (1170 amino acids). The deduced CISP protein sequence is 89% identical to that of human thrombospondin-2 (TSP2), but only 61% identical to that of bovine TSP1, confirming that CISP is the bovine ortholog of TSP2. The bovine TSP2 sequence aligned perfectly with human, mouse, and chicken TSP2 sequences, except for a gap of 2 amino acids located in a linker region. All 58 cysteine residues that are conserved in other species were present in the bovine sequence as well as most of the functional domains. Most endocrine tissues (adrenal cortex, testis, ovary, and placenta) appeared to express TSP2, as determined by Western blot analysis. The highest levels of TSP2 protein were found in the adrenal cortex, followed by the heart, spleen, brain, and kidney. A differential extent of N-glycosylation or tissular proteolytic maturation may be responsible for the mol wt differences observed between bovine TSP2 detected in the medium from primary cultures and that in fresh tissue extracts. The immunohistochemical analysis of the distribution of TSP2 in the bovine adrenal gland revealed that the protein is much more abundant in the external zones (zona glomerulosa and zona fasciculata) than in the internal reticularis zone, a pattern similar to that reported for ACTH receptors. This distribution clearly suggests that TSP2 is a candidate relay protein for a subset of ACTH actions in the adrenal cortex.

Regulation of the three-dimensional organization of thyroid epithelial cells into follicle structures by the matricellular protein, thrombospondin-1

Thyroid epithelial cells in primary culture have the capacity to organize into thyroid-specific three-dimensional structures, the follicles, in response to TSH. We studied whether thrombospondin 1 (TSP1), which represents, besides thyroglobulin, the main protein secreted by thyroid cells, could play a role in the process of folliculogenesis. TSH promoted follicle formation and inhibited TSP1 production. On the contrary, the phorbol ester, 12-O-tetradecanoyl-phorbol 13-acetate (1-100 nM) prevented TSH-induced follicle formation and strongly increased the synthesis of TSP1. Activation of TSP1 synthesis was dependent upon messenger RNA synthesis. Transforming growth factor-beta, like 12-O-tetradecanoyl-phorbol 13-acetate, increased TSP1 synthesis and prevented TSH-induced follicle formation. Thus, signaling molecules that depressed or conversely activated TSP1 production, respectively promoted or prevented thyroid folliculogenesis. TSP1, purified from platelets, was devoid of effect on cell substratum attachment, but exerted a concentration-dependent inhibition of the TSH-activated reconstitution of thyroid follicles (half-inhibition at 40 microg/ml). TSP1 exhibited the same effect when added to thyroid cell aggregates representing primitive follicle structures. Our data suggest that the control of thyroid follicle formation may operate at least in part through regulation of the production of the matricellular protein TSP1, which acts as a negative modulator of the cell-cell adhesion process involved in thyroid follicle morphogenesis.

Restricted localization of thrombospondin-2 protein during mouse embryogenesis: a comparison to thrombospondin-1

Thrombospondin-1 and -2 (TSP1 and TSP2) are multifunctional, multimodular extracellular matrix proteins encoded by separate genes. We compared the distributions of TSP1 and TSP2 in mouse embryos (day 10 and later) by immunohistochemistry. TSP1 was detected on day 10 in the heart and intestinal epithelium, on day 11 in megakaryocytes, and on day 14 in the lung. TSP2 was not detected until day 14, with strongest staining in mesenchymal condensation that gives rise to cartilage and bone. The distribution of TSP2 was different from but overlapped with the distribution of TSP1. TSP1 was found in cartilage proper with diminished staining around chondrocytes undergoing differentiation and hypertrophy, whereas TSP2 was restricted to the matrix surrounding chondrocytes of the growth zone cartilage. TSP2 and TSP1 were both expressed in centers of intramembranous ossification that form the skull bones, in reticular dermis, on the apical surface of nasal epithelium, in skeletal muscle, and in the sheath surrounding vibrissae. Areas of exclusive staining for TSP2 included the perichondrium surrounding the cartilage of the nasal cavities, developing bone of the lower mandible, and adrenal gland. The distinct localizations of TSP1 and TSP2 indicate that the two proteins have specific functions during mouse embryogenesis.

Analysis of small latent transforming growth factor-beta complex formation and dissociation by surface plasmon resonance. Absence of direct interaction with thrombospondins

Transforming growth factor-beta (TGFbeta) is a pluripotent regulator of cell growth and differentiation. The growth factor is expressed as a latent complex that must be converted to an active form before interacting with its ubiquitous high affinity receptors. This conversion involves the release of the mature TGFbeta through disruption of the noncovalent interactions with its propeptide or latency associated protein (LAP). Complex formation or dissociation between LAP and TGFbeta plays a very important role in TGFbeta biological activity at different steps. To further characterize the kinetic parameters of this interaction, we have employed surface plasmon resonance biosensor methodology. Using this technique, we observed real time association of LAP with mature TGFbeta1. The complex formation showed an equilibrium Kd around 3-7 nM. Furthermore, we observed dissociation of the complex in the presence of extreme pH, chaotropic agents, or plasmin, confirming their effects on TGFbeta activation. The same approach was used to examine whether latent TGFbeta1 could interact with thrombospondins, previously described as activators of latent TGFbeta. Using this method, we could not detect any direct interaction of thrombospondins with either LAP alone, TGFbeta1 alone, or the small latent TGFbeta1 complex. This suggests that activation of latent TGFbeta1 complex by thrombospondins is through an indirect mechanism.

Expression of laminin and its possible role in adrenal cortex homeostasis

The adult mammalian adrenal cortex undergoes permanent regeneration. This process implies a cellular proliferation step restricted to the external zone of the tissue, and a subsequent centripetal cell migration during which phenotypic transition from glomerulosa into fasciculata and reticularis cells and elimination of senescent cells through apoptosis occur. As the molecular mechanisms implied in adrenocortical cell migration are still generally unknown, we addressed that question in the present study. Of several extracellular matrix proteins tested, laminin was the most potent chemotactic and haptotactic factor for bovine fasciculata adrenocortical cells. The maximal chemotactic effect (3-fold stimulation) was observed with 50-75 micrograms/ml laminin, whereas the haptotactic effect (3.5-fold stimulation) plateaued for laminin concentrations in the coating solution over 25 micrograms/ml. Using an anti-Engelbreth-Holm-Swarm laminin antibody, we could demonstrate that adrenocortical cells actively synthesize and secrete Engelbreth-Holm-Swarm-laminin, with the A chain produced in limiting quantities. ACTH treatment of adrenocortical cells specifically induced a 2.7- to 4.5-fold increase in A chain synthesis, resulting in a corresponding increase in the amount of secreted laminin. The distribution of laminin in the adrenal cortex tissue was then evaluated by standard immunohistochemistry. The protein appeared to be uniformly expressed in the three zones of the cortex. This observation does not favor the hypothesis that laminin acts as an attractant driving centripetal cell migration. Laminin, which is synthesized under the control of the systemic hormone ACTH, appears as a permissive factor that facilitates proper homeostasis of the adrenocortical tissue.

Opposite regulation of thrombospondin-1 and corticotropin-induced secreted protein/thrombospondin-2 expression by adrenocorticotropic hormone in adrenocortical cells

Corticotropin-induced secreted protein (CISP) is a trimeric glycoprotein secreted by primary cultures of bovine adrenortical cells in response to adrenocorticotropic hormone (ACTH). This protein was recently purified in our laboratory, and its N-terminal amino-acid sequence revealed a significant similarity with thrombospondin-2 (TSP2). We report here the nucleotide sequence of a 386 bp RT-PCR fragment specific for CISP. The deduced protein sequence shares 84% identity with the N-terminal portion of mature human TSP2, suggesting that CISP is its bovine counterpart. Northern analysis of adrenocortical cell RNA using the above cDNA fragment as a probe revealed a 6.0 kb CISP/TSP2 mRNA whose abundance was increased nearly fivefold following a 24 h cell treatment with 10(-7) M ACTH. Under the same conditions, the expression of TSP1 mRNA was reduced by tenfold. The protein levels of TSP1 and CISP/TSP2 varied accordingly with their respective mRNA levels, as shown by immunoprecipitation and immunofluorescence experiments. Taken together, these data show that ACTH induces a dramatic shift in the pattern of adrenocortical cell thrombospondin expression from TSP1 to CISP/TSP2. This observation suggests that these two members of the thrombospondin family exert distinct biological functions in the adrenal cortex. This hypothesis is further supported by the observation that anti-CISP antibodies inhibit the maintenance of the morphological changes of bovine adrenocortical cells induced by ACTH, whereas anti-TSP1 antibodies do not.

Distinct effects of thrombospondin-1 and CISP/thrombospondin-2 on adrenocortical cell spreading

Corticotropin-induced secreted protein (CISP) is a trimeric protein secreted by bovine adrenocortical cells in response to ACTH, that is likely to represent the bovine form of thrombospondin-2 (TSP2). This study was aimed at delineating the respective effects of CISP/TSP2 and TSP1 (thrombospondin-1) on adrenocortical cell attachment and spreading. TSP1 and CISP/TSP2 were found to slightly reduce the attachment of adrenocortical cells to plastic in the presence of serum but exhibited a pronounced differential effect on cell spreading. CISP/TSP2 inhibited adrenocortical cell spreading in a dose-dependent manner (maximal effect with 40 micrograms/ml) whereas TSP1 (up to 100 micrograms/ml) did not influence this process. The inhibition of spreading was observed whether plates were coated with CISP/TSP2 alone or with a mixture of CISP/TSP2 and fibronectin. We suggest that the inhibition of in vitro adrenocortical cell spreading by CISP/TSP2 is indicative of an implication of this protein in the migration of adrenocortical cells in vivo.