Faculty Bibliography

Prolactinomas are the most prevalent type of secreting pituitary tumors in humans and generally respond well to a medical therapy with dopamine agonists. However, for patients exhibiting resistance to dopaminergic drugs, alternative treatments are desired. Antiangiogenic strategies might represent a potential therapy for these tumors. Thrombospondin 1 (TSP-1) is a large multifunctional glycoprotein involved in multiple biological processes including angiogenesis, apoptosis, and activation of TGF-beta1. Because tumors that overexpress TSP-1 grow more slowly, have fewer metastases, and have decreased angiogenesis, TSP-1 provides a novel target for cancer treatment. ABT-510 and ABT-898 are TSP-1 synthetic analogs that mimic its antiangiogenic action. In the present study, we explored the potential effect of ABT-510 and ABT-898 on experimental prolactinomas induced by chronic diethylstilbestrol (DES) treatment in female rats. We demonstrated that a 2-wk treatment with ABT-510 and ABT-898 counteracted the increase in pituitary size and serum prolactin levels as well as the pituitary proliferation rate induced by DES. These inhibitory effects on tumor growth could be mediated by the antiangiogenic properties of the drugs. We also demonstrated that ABT-510 and ABT-898, in addition to their described antiangiogenic effects, increased active TGF-beta1 level in the tumors. We postulate that the recovery of the local cytokine activation participates in the inhibition of lactotrope function. These results place these synthetic TSP-1 analogs as potential alternative or complementary treatments in dopamine agonist-resistant prolactinomas.

Latent transforming growth factor beta (TGF-beta) binding proteins (LTBPs) are large extracellular glycoproteins structurally similar to fibrillins. They perform intricate and important roles in the extracellular matrix (ECM) and perturbations of their function manifest as a wide range of diseases. LTBPs are major regulators of TGF-beta bioavailability and action. In addition, LTBPs interact with other ECM proteins-from cytokines to large multi-factorial aggregates like microfibrils and elastic fibers, affecting their genesis, structure, and performance. In the present article, we review recent advancements in the field and relate the complex roles of LTBP in development and homeostasis. J. Cell. Biochem. 113: 410-418, 2012. (c) 2011 Wiley Periodicals, Inc

BACKGROUND: Breast to bone metastases frequently induce a 'vicious cycle' in which osteoclast mediated bone resorption and proteolysis results in the release of bone matrix sequestered factors that drive tumor growth. While osteoclasts express numerous proteinases, analysis of human breast to bone metastases unexpectedly revealed that bone forming osteoblasts were consistently positive for the proteinase, MMP-2. Given the role of MMP-2 in extracellular matrix degradation and growth factor/cytokine processing, we tested whether osteoblast derived MMP-2 contributed to the vicious cycle of tumor progression in the bone microenvironment. METHODOLOGY/PRINCIPAL FINDINGS: To test our hypothesis, we utilized murine models of the osteolytic tumor-bone microenvironment in immunocompetent wild type and MMP-2 null mice. In longitudinal studies, we found that host MMP-2 significantly contributed to tumor progression in bone by protecting against apoptosis and promoting cancer cell survival (caspase-3; immunohistochemistry). Our data also indicate that host MMP-2 contributes to tumor induced osteolysis (muCT, histomorphometry). Further ex vivo/in vitro experiments with wild type and MMP-2 null osteoclast and osteoblast cultures identified that 1) the absence of MMP-2 did not have a deleterious effect on osteoclast function (cd11B isolation, osteoclast differentiation, transwell migration and dentin resorption assay); and 2) that osteoblast derived MMP-2 promoted tumor survival by regulating the bioavailability of TGFbeta, a factor critical for cell-cell communication in the bone (ELISA, immunoblot assay, clonal and soft agar assays). CONCLUSION/SIGNIFICANCE: Collectively, these studies identify a novel 'mini-vicious cycle' between the osteoblast and metastatic cancer cells that is key for initial tumor survival in the bone microenvironment. In conclusion, the findings of our study suggest that the targeted inhibition of MMP-2 and/or TGFbeta would be beneficial for the treatment of bone metastases

In congenital heart block (CHB), binding of maternal anti-SSA/Ro Abs to fetal apoptotic cardiocytes impairs their removal by healthy cardiocytes and increases urokinase plasminogen activator (uPA)/uPA receptor (uPAR)-dependent plasmin activation. Because the uPA/uPAR system plays a role in TGF-beta activation, we evaluated whether anti-Ro binding to apoptotic cardiocytes enhances plasmin-mediated activation of TGF-beta, thereby promoting a profibrosing phenotype. Supernatants from cocultures of healthy cardiocytes and apoptotic cardiocytes bound by IgG from a mother whose child had CHB (apoptotic-CHB-IgG [apo-CHB-IgG]) exhibited significantly increased levels of active TGF-beta compared with supernatants from cocultures of healthy cardiocytes and apoptotic cardiocytes preincubated with IgG from a healthy donor. Treatment of the culture medium with anti-TGF-beta Ab or TGF-beta inhibitor (SB431542) abrogated the luciferase response, thereby confirming TGF-beta dependency. Increased uPA levels and activity were present in supernatants generated from cocultures of healthy cardiocytes and apo-CHB-IgG cardiocytes compared with healthy cardiocytes and apoptotic cardiocytes preincubated with IgG from a healthy donor, respectively. Treatment of apo-CHB-IgG cardiocytes with anti-uPAR or anti-uPA Abs or plasmin inhibitor aprotinin prior to coculturing with healthy cardiocytes attenuated TGF-beta activation. Supernatants derived from cocultures of healthy cardiocytes and apo-CHB-IgG cardiocytes promoted Smad2 phosphorylation and fibroblast transdifferentiation, as evidenced by increased smooth muscle actin and collagen expression, which decreased when fibroblasts were treated with supernatants from cocultures pretreated with uPAR Abs. These data suggested that binding of anti-Ro Abs to apoptotic cardiocytes triggers TGF-beta activation, by virtue of increasing uPAR-dependent uPA activity, thus initiating and amplifying a cascade of events that promotes myofibroblast transdifferentiation and scar

Dopamine, acting through the dopamine type 2 receptor (Drd2), is the main inhibitor of pituitary prolactin (PRL) secretion and lactotroph proliferation. TGF-beta1 is involved, at least in part, in mediating these actions. It was described that TGF-beta1 synthesis in rat pituitary lactotrophs is up-regulated by dopamine and down-regulated by estradiol. TGF-beta1 is secreted as a large latent complex. The local regulation of cytokine activation in the pituitary has not yet been explored. In this work, we studied pituitary active and total TGF-beta1 content, as well as TGF-beta1 mRNA, and the in vivo role of dopamine and estradiol on pituitary TGF-beta1 levels. Adult female mice (wild type), and female mice with a null mutation in the Drd2 (Drd2(-/-)), were used. The loss of dopaminergic tone induced a decrease in TGF-beta1 mRNA expression, in active and total cytokine content, and in TGF-beta type II receptor expression. Dopamine regulation of pituitary TGF-beta1 activation process was inferred by the inhibition of active cytokine by in vivo sulpiride treatment. Interestingly, in the absence of dopaminergic tone, estradiol induced a strong increase in active TGF-beta1. PRL secretion correlated with active, but not total cytokine. TGF-beta1 inhibitory action on lactotroph proliferation and PRL secretion was decreased in Drd2(-/-) pituitary cells, in correlation with decreased TGF-beta type II receptor. The study of the TGF-beta1 activation process and its regulation is essential to understand the cytokine activity. As an intermediary of dopamine inhibition of lactotroph function, TGF-beta1 and local activators may be important targets in the treatment of dopamine agonist-resistant prolactinomas

The latent TGF-beta binding proteins (LTBP-1 -3, and -4) assist in the secretion and localization of latent TGF-beta molecules. Ltbp3(-/-) and Ltbp4S(-/-) mice have distinct phenotypes and only in the lungs does deficiency of either Ltbp-3 or Ltbp-4 cause developmental abnormalities. To determine if these two LTBPs have additional common functions, we generated mice deficient for both Ltbp-3 and Ltbp-4S. The only novel defect in Ltbp3(-/-);Ltbp4S(-/-) mice was an early lethality compared to mice with single mutations. In addition lung abnormalities were exacerbated and the terminal air sac septation defect was more severe in Ltbp3(-/-);Ltbp4S(-/-) mice than in Ltbp4S(-/-) mice. Decreased cellularity of Ltbp3(-/-);Ltbp4S(-/-) lungs was correlated with higher rate of apoptosis in newborn lungs of Ltbp3(-/-);Ltbp4S(-/-) animals compared to WT, Ltbp3(-/-), and Ltbp4S(-/-) mice. No differences in the maturation of the major lung cell types were discerned between the single and double mutant mice. However, the distribution of type 2 cells and myofibroblasts was abnormal, and myofibroblast segregation in some areas might be an indication of early fibrosis. We also observed differences in ECM composition between Ltbp3(-/-);Ltbp4S(-/-) and Ltbp4S(-/-) lungs after birth, reflected in decreased incorporation of fibrillin-1 and -2 in Ltbp3(-/-);Ltbp4S(-/-) matrix. The function of the lungs of Ltbp3(-/-);Ltbp4S(-/-) mice after the first week of life was potentially further compromised by macrophage infiltration, as proteases secreted from macrophages might exacerbate developmental emphysema. Together these data indicate that LTBP-3 and -4 perform partially overlapping functions only in the lungs

Transforming Growth Factor beta (TGF-beta) is crucial for valve development and homeostasis. The long form of Latent TGF-beta binding protein 1 (LTBP1L) covalently binds all TGF-beta isoforms and regulates their bioavailability. Ltbp1L expression analysis during valvulogenesis revealed two patterns of Ltbp1L production: an early one (E9.5-11.5) associated with endothelial-to-mesenchymal transformation (EMT); and a late one (E12.5 to birth) contemporaneous with valve remodeling. Similarly, histological analysis of Ltbp1L(-/-) developing valves identified two different pathologies: generation of hypoplastic endocardial cushions in early valvulogenesis, followed by development of hyperplastic valves in late valvulogenesis. Ltbp1L promotes valve EMT, as Ltbp1L absence yields hypoplastic endocardial cushions in vivo and attenuated EMT in vitro. Ltbp1L(-/-) valve hyperplasia in late valvuogenesis represents a consequence of prolonged EMT. We demonstrate that Ltbp1L is a major regulator of Tgf-beta activity during valvulogenesis since its absence results in a perturbed Tgf-beta pathway that causes all Ltbp1L(-/-) valvular defects. Developmental Dynamics, 2011. (c) 2010 Wiley-Liss, Inc