Shanna A. Arnold

SPARC: a matricellular regulator of tumorigenesis.

Although many clinical studies have found a correlation of SPARC expression with malignant progression and patient survival, the mechanisms for SPARC function in tumorigenesis and metastasis remain elusive. The activity of SPARC is context- and cell-type-dependent, which is highlighted by the fact that SPARC has shown seemingly contradictory effects on tumor progression in both clinical correlative studies and in animal models. The capacity of SPARC to dictate tumorigenic phenotype has been attributed to its effects on the bioavailability and signaling of integrins and growth factors/chemokines. These molecular pathways contribute to many physiological events affecting malignant progression, including extracellular matrix remodeling, angiogenesis, immune modulation and metastasis. Given that SPARC is credited with such varied activities, this review presents a comprehensive account of the divergent effects of SPARC in human cancers and mouse models, as well as a description of the potential mechanisms by which SPARC mediates these effects. We aim to provide insight into how a matricellular protein such as SPARC might generate paradoxical, yet relevant, tumor outcomes in order to unify an apparently incongruent collection of scientific literature.

Lack of host SPARC enhances vascular function and tumor spread in an orthotopic murine model of pancreatic carcinoma

SUMMARY Utilizing subcutaneous tumor models, we previously validated SPARC (secreted protein acidic and rich in cysteine) as a key component of the stromal response, where it regulated tumor size, angiogenesis and extracellular matrix deposition. In the present study, we demonstrate that pancreatic tumors grown orthotopically in Sparc-null (Sparc−/−) mice are more metastatic than tumors grown in wild-type (Sparc+/+) littermates. Tumors grown in Sparc−/− mice display reduced deposition of fibrillar collagens I and III, basement membrane collagen IV and the collagen-associated proteoglycan decorin. In addition, microvessel density and pericyte recruitment are reduced in tumors grown in the absence of host SPARC. However, tumors from Sparc−/− mice display increased permeability and perfusion, and a subsequent decrease in hypoxia. Finally, we found that tumors grown in the absence of host SPARC exhibit an increase in alternatively activated macrophages. These results suggest that increased tumor burden in the absence of host SPARC is a consequence of reduced collagen deposition, a disrupted vascular basement membrane, enhanced vascular function and an immune-tolerant, pro-metastatic microenvironment.

Forced expression of MMP9 rescues the loss of angiogenesis and abrogates metastasis of pancreatic tumors triggered by the absence of host SPARC

Pancreatic adenocarcinoma is characterized by desmoplasia, local invasion, and metastasis. These features are regulated in part by MMP9 and SPARC. To explore the interaction of SPARC and MMP9 in cancer, we first established orthotopic pancreatic tumors in SPARC-null and wild-type mice with the murine pancreatic adenocarcinoma cell line, PAN02. MMP9 expression was higher in tumors from wild-type compared to SPARC-null mice. Coincident with lower MMP9 expression, tumors grown in SPARC-null mice were significantly larger, had decreased ECM deposition and reduced microvessel density compared to wild-type controls. In addition, metastasis was enhanced in the absence of host SPARC. Therefore, we next analyzed the orthotopic tumor growth of PAN02 cells transduced with MMP9 or a control empty vector. Forced expression of MMP9 by the PAN02 cells resulted in larger tumors in both wild-type and SPARC-null animals compared to empty vector controls and further diminished ECM deposition. Importantly, forced expression of MMP9 within the tumor reversed the decrease in angiogenesis and abrogated the metastatic potential displayed by control tumors grown in SPARC-null mice. Finally, contrary to the in vivo results, MMP9 increased cell migration in vitro, which was blocked by the addition of SPARC. These results suggest that SPARC and MMP9 interact to regulate many stages of tumor progression including ECM deposition, angiogenesis and metastasis.

Losartan Slows Pancreatic Tumor Progression and Extends Survival of SPARC-Null Mice by Abrogating Aberrant TGFβ Activation

Pancreatic adenocarcinoma, a desmoplastic disease, is the fourth leading cause of cancer-related death in the Western world due, in large part, to locally invasive primary tumor growth and ensuing metastasis. SPARC is a matricellular protein that governs extracellular matrix (ECM) deposition and maturation during tissue remodeling, particularly, during wound healing and tumorigenesis. In the present study, we sought to determine the mechanism by which lack of host SPARC alters the tumor microenvironment and enhances invasion and metastasis of an orthotopic model of pancreatic cancer. We identified that levels of active TGFβ1 were increased significantly in tumors grown in SPARC-null mice. TGFβ1 contributes to many aspects of tumor development including metastasis, endothelial cell permeability, inflammation and fibrosis, all of which are altered in the absence of stromal-derived SPARC. Given these results, we performed a survival study to assess the contribution of increased TGFβ1 activity to tumor progression in SPARC-null mice using losartan, an angiotensin II type 1 receptor antagonist that diminishes TGFβ1 expression and activation in vivo. Tumors grown in SPARC-null mice progressed more quickly than those grown in wild-type littermates leading to a significant reduction in median survival. However, median survival of SPARC-null animals treated with losartan was extended to that of losartan-treated wild-type controls. In addition, losartan abrogated TGFβ induced gene expression, reduced local invasion and metastasis, decreased vascular permeability and altered the immune profile of tumors grown in SPARC-null mice. These data support the concept that aberrant TGFβ1-activation in the absence of host SPARC contributes significantly to tumor progression and suggests that SPARC, by controlling ECM deposition and maturation, can regulate TGFβ availability and activation.

ALCAM/CD166 Is a TGF-β–Responsive Marker and Functional Regulator of Prostate Cancer Metastasis to Bone

The dissemination of prostate cancer to bone is a common, incurable aspect of advanced disease. Prevention and treatment of this terminal phase of prostate cancer requires improved molecular understanding of the process as well as markers indicative of molecular progression. Through biochemical analyses and loss-of-function in vivo studies, we demonstrate that the cell adhesion molecule, activated leukocyte cell adhesion molecule (ALCAM), is actively shed from metastatic prostate cancer cells by the sheddase ADAM17 in response to TGF-β. Not only is this posttranslational modification of ALCAM a marker of prostate cancer progression, the molecule is also required for effective metastasis to bone. Biochemical analysis of prostate cancer cell lines reveals that ALCAM expression and shedding is elevated in response to TGF-β signaling. Both in vitro and in vivo shedding is mediated by ADAM17. Longitudinal analysis of circulating ALCAM in tumor-bearing mice revealed that shedding of tumor, but not host-derived ALCAM is elevated during growth of the cancer. Gene-specific knockdown of ALCAM in bone-metastatic PC3 cells greatly diminished both skeletal dissemination and tumor growth in bone. The reduced growth of ALCAM knockdown cells corresponded to an increase in apoptosis (caspase-3) and decreased proliferation (Ki67). Together, these data demonstrate that the ALCAM is both a functional regulator as well as marker of prostate cancer progression.

Integrin-Free Tetraspanin CD151 Can Inhibit Tumor Cell Motility upon Clustering and Is a Clinical Indicator of Prostate Cancer Progression

Normal physiology relies on the organization of transmembrane proteins by molecular scaffolds, such as tetraspanins. Oncogenesis frequently involves changes in their organization or expression. The tetraspanin CD151 is thought to contribute to cancer progression through direct interaction with the laminin-binding integrins α3β1 and α6β1. However, this interaction cannot explain the ability of CD151 to control migration in the absence of these integrins or on non-laminin substrates. We demonstrate that CD151 can regulate tumor cell migration without direct integrin binding and that integrin-free CD151 (CD151(free)) correlates clinically with tumor progression and metastasis. Clustering CD151(free) through its integrin-binding domain promotes accumulation in areas of cell-cell contact, leading to enhanced adhesion and inhibition of tumor cell motility in vitro and in vivo. CD151(free) clustering is a strong regulator of motility even in the absence of α3 expression but requires PKCα, suggesting that CD151 can control migration independent of its integrin associations. The histologic detection of CD151(free) in prostate cancer correlates with poor patient outcome. When CD151(free) is present, patients are more likely to recur after radical prostatectomy and progression to metastatic disease is accelerated. Multivariable analysis identifies CD151(free) as an independent predictor of survival. Moreover, the detection of CD151(free) can stratify survival among patients with elevated prostate-specific antigen levels. Cumulatively, these studies demonstrate that a subpopulation of CD151 exists on the surface of tumor cells that can regulate migration independent of its integrin partner. The clinical correlation of CD151(free) with prostate cancer progression suggests that it may contribute to the disease and predict cancer progression.

Transfusion reactions in pediatric compared with adult patients: a look at rate, reaction type, and associated products

The majority of reports on transfusion reactions address adult patients. Less is known about the types, incidence, and other clinical details of transfusion reactions in pediatric populations. Furthermore, to our knowledge, there have been no previous reports directly comparing these aspects between adults and pediatric patient populations to assess if there are differences.

Secreted protein acidic and rich in cysteine as a regulator of murine ovarian cancer growth and chemosensitivity

OBJECTIVE Secreted protein acidic and rich in cysteine (SPARC) influences the growth of several solid tumors. Our objectives were to determine the effect of SPARC on the growth and response to cisplatin therapy of platinum-resistant ovarian cancer. STUDY DESIGN SPARC expression was determined in 4 platinum-resistant ovarian cancer cell lines. The effect of increasing SPARC on cell proliferation was determined in vitro. The effect of host-derived SPARC on tumor growth and response to therapy was determined in vivo using the murine ovarian cancer cell line, OSEID8, which was injected into the peritoneum of wild-type (WT) and SPARC-null (SP-/-) mice. RESULTS Forced expression of SPARC decreased growth of platinum-resistant ovarian cancer cell lines in vitro. In vivo, tumor growth was more aggressive in the absence of host-derived SPARC resulting in decreased survival compared with WT mice (P = .005). Cisplatin did not improve survival of WT mice. In contrast, cisplatin therapy resulted in a significant survival advantage (P = .0048) and decreased tumor volume (P = .02) in SP-/- animals. CONCLUSION We conclude that SPARC is an important extracellular matrix protein that regulates the growth and chemosensitivity of ovarian cancer. In general, SPARC appears to control tumor cell growth but also impede the efficacy of cisplatin therapy. Therefore, selective inhibition of SPARC may provide an attractive strategy for increasing the efficacy of therapy in platinum-resistant ovarian tumors.

Elevated ALCAM Shedding in Colorectal Cancer Correlates with Poor Patient Outcome

Molecular biomarkers of cancer are needed to assist histologic staging in the selection of treatment, outcome risk stratification, and patient prognosis. This is particularly important for patients with early-stage disease. We show that shedding of the extracellular domain of activated leukocyte cell adhesion molecule (ALCAM) is prognostic for outcome in patients with colorectal cancer (CRC). Previous reports on the prognostic value of ALCAM expression in CRC have been contradictory and inconclusive. This study clarifies the prognostic value of ALCAM by visualizing ectodomain shedding using a dual stain that detects both the extracellular and the intracellular domains in formalin-fixed tissue. Using this novel assay, 105 patients with primary CRCs and 12 normal mucosa samples were evaluated. ALCAM shedding, defined as detection of the intracellular domain in the absence of the corresponding extracellular domain, was significantly elevated in patients with CRC and correlated with reduced survival. Conversely, retention of intact ALCAM was associated with improved survival, thereby confirming that ALCAM shedding is associated with poor patient outcome. Importantly, analysis of patients with stage II CRC showed that disease-specific survival is significantly reduced for patients with elevated ALCAM shedding (P = 0.01; HR, 3.0), suggesting that ALCAM shedding can identify patients with early-stage disease at risk of rapid progression.

MAGI-2 in prostate cancer: an immunohistochemical study ☆

Membrane-associated guanylate kinase, WW and PDZ domain-containing protein 2 (MAGI-2) is a scaffolding protein that links cell adhesion molecules, receptors, and signaling molecules to the cytoskeleton and maintains the architecture of cell junctions. MAGI-2 gene rearrangements have recently been described in prostate cancer. We studied the immunohistochemical expression of MAGI-2 protein in prostate tissue. Seventy-eight radical prostatectomies were used to construct 3 tissue microarrays consisting of 512 cores, including benign tissue, benign prostatic hyperplasia, high-grade prostatic intraepithelial neoplasia (HGPIN), and adenocarcinoma, Gleason patterns 3 to 5. Immunohistochemistry for phosphatase and tensin homologue (PTEN) and double-stain MAGI-2/p63 was performed and analyzed by visual and image analysis, the latter as percent of analyzed area (%AREA), and mean optical density multiplied by %AREA (STAIN). By visual and image analysis, MAGI-2 was significantly higher in adenocarcinoma and HGPIN compared with benign (benign versus HGPIN P < .001; benign versus adenocarcinoma, P < .001). HGPIN and adenocarcinoma did not significantly differ by either modality. Using visual intensity to distinguish benign tissue and adenocarcinoma, a receiver operating curve yielded an area under the curve of 0.902. A STAIN threshold of 1470 yielded a sensitivity of 0.66 and specificity of 0.96. There was a significant correlation between PTEN and MAGI-2 staining for normal and benign prostatic hyperplasia, but this was lost in HGPIN and cancer. We conclude that MAGI-2 immunoreactivity is elevated in prostate cancer and HGPIN compared with normal tissue, and suggest that MAGI-2 may contribute to prostate carcinogenesis. This is the first report of MAGI-2 staining by immunohistochemistry in prostate cancer.