Tumor growth is essentially the result of an evolving cross-talk between malignant and surrounding stromal cells (fibroblasts, endothelial cells and inflammatory cells). This heterogeneous mass of extracellular matrix and intermingled cells interact through cell-cell and cell-matrix contacts. Malignant cells also secrete soluble proteins that reach neighbor stromal cells, forcing them to provide the soil on which they will grow and metastasize. Different studies including expression array analysis identified the matricellular protein SPARC as a marker of poor prognosis in different cancer types. Further evidence demonstrated that high SPARC levels are often associated with the most aggressive and highly metastatic tumors. Here we describe the most recent evidence that links SPARC with human cancer progression, the controversy regarding its role in certain human cancers and the physiological processes in which SPARC is involved: epithelial-mesenchymal transition, immune surveillance and angiogenesis. Its relevance as a potential target in cancer therapy is also discussed.

Interleukin-1␤ (IL-1) expression is associated with a spectrum of neuroinflammatory processes related to chronic neurodegenerative diseases. The single-bolus microinjection of IL-1 into the central nervous system (CNS) parenchyma gives rise to delayed and localized neutrophil recruitment, transient blood-brain barrier (BBB) breakdown, but no overt damage to CNS integrity. However, acute microinjections of IL-1 do not mimic the chronic IL-1 expression, which is a feature of many CNS diseases. To investigate the response of the CNS to chronic IL-1 expression, we injected a recombinant adenovirus expressing IL-1 into the striatum. At the peak of IL-1 expression (days 8 and 14 post-injection), there was a marked recruitment of neutrophils, vasodilatation, and breakdown of the BBB. Microglia and astrocyte activation was evident during the first 14 days post-injection. At days 8 and 14, extensive demyelination was observed but the number of neurons was not affected by any treatment. Finally, at 30 days, signs of inflammation were no longer present, there was evidence of tissue reorganization, the BBB was intact, and the process of remyelination was noticeable. In summary, our data show that chronic expression of IL-1, in contrast to its acute delivery, can reversibly damage CNS integrity and implicates this cytokine or downstream components as major mediators of demyelination in chronic inflammatory and demyelinating diseases.

The expression of secreted protein acidic and rich in cysteine (SPARC) has been associated with the malignant progression of different types of human cancer. SPARC was associated with tumor cell capacity to migrate and invade, although its precise role in tumor progression is still elusive. In the present study, we show that SPARC produced by melanoma cells modulates the antitumor activity of polymorphonuclear leukocytes (PMN). Administration to nude mice of human melanoma cells in which SPARC expression was transiently or stably knocked down by antisense RNA (SPARC-sup cells) promoted PMN recruitment and obliterated tumor growth even when SPARC-sup cells accounted for only 10% of injected malignant cells. In addition, SPARC-sup cells stimulated the in vitro migration and triggered the antimelanoma cytotoxic capacity of human PMN, an effect that was reverted in the presence of SPARC purified from melanoma cells or by reexpressing SPARC in SPARC-sup cells. Leukotrienes, interleukin 8, and growth-related oncogene, in combination with Fas ligand and interleukin 1, mediated SPARC effects. These data indicate that SPARC plays an essential role in tumor evasion from immune surveillance through the inhibition of the antitumor PMN activity. (Cancer Res 2005; 65(12): 5123-32)

Tumor growth is essentially the result of an evolving cross-talk between malignant and surrounding stromal cells (fibroblasts, endothelial cells and inflammatory cells). This heterogeneous mass of extracellular matrix and intermingled cells interact through cell-cell and cell-matrix contacts. Malignant cells also secrete soluble proteins that reach neighbor stromal cells, forcing them to provide the soil on which they will grow and metastasize. Different studies including expression array analysis identified the matricellular protein SPARC as a marker of poor prognosis in different cancer types. Further evidence demonstrated that high SPARC levels are often associated with the most aggressive and highly metastatic tumors. Here we describe the most recent evidence that links SPARC with human cancer progression, the controversy regarding its role in certain human cancers and the physiological processes in which SPARC is involved: epithelial-mesenchymal transition, immune surveillance and angiogenesis. Its relevance as a potential target in cancer therapy is also discussed.

This is the first study to demonstrate that knockdown of hepatic SPARC expression ameliorates thioacetamide-induced liver fibrosis in rats with chronic liver injury. SPARC is a potential target for gene therapy in liver fibrosis.

SPARC (secreted protein acidic and rich in cysteine) is a matricellular protein whose overexpression in malignant or tumor-stromal cells is often associated with increased aggressiveness and bad prognosis in a wide range of human cancer types, particularly melanoma. We established the impact that changes in the level of SPARC produced by malignant cells and neighboring stromal cells have on melanoma growth. Melanoma cell growth in monolayer was only slightly affected by changes in SPARC levels. However, melanoma growth in spheroids was strongly inhibited upon SPARC hyperexpression and conversely enhanced when SPARC expression was downregulated. Interestingly, SPARC overexpression in neighboring fibroblasts had no effect on spheroid growth irrespective of SPARC levels expressed by the melanoma cells, themselves. Downregulation of SPARC expression in melanoma cells induced their rejection in vivo through a mechanism mediated exclusively by host polymorphonuclear cells. On the other hand, SPARC hyperexpression enhanced vascular density, collagen deposition, and fibroblast recruitment in the surrounding stroma without affecting melanoma growth. In agreement with the in vitro data, overexpression of SPARC in co-injected fibroblasts did not affect melanoma growth in vivo. All the data indicate that melanoma growth is not subject to regulation by exogenous SPARC, nor by stromal organization, but only by SPARC levels produced by the malignant cells themselves.

Secreted protein, acidic and rich in cysteines (SPARC) is a secreted protein associated with increased aggressiveness of different human cancer types. In order to identify downstream mediators of SPARC activity, we performed a 2-DE proteomic analysis of human melanoma cells following antisense-mediated downregulation of SPARC expression. We found 23/504 differential spots, 15 of which were identified by peptide fingerprinting analysis. Three of the differential proteins (N-cadherin (N-CAD), clusterin (CLU), and HSP27) were validated by immunoblotting, confirming decreased levels of N-CAD and CLU and increased amounts of HSP27 in conditioned media of cells with diminished SPARC expression. Furthermore, transient knock down of SPARC expression in melanoma cells following adenoviral-mediated transfer of antisense RNA confirmed these changes. We next developed two different RNAs against SPARC that were able to inhibit in vivo melanoma cell growth. Immunoblotting of the secreted fraction of RNAi-transfected melanoma cells confirmed that downregulation of SPARC expression promoted decreased levels of N-CAD and CLU and increased secretion of HSP27. Transient re-expression of SPARC in SPARC-downregulated cells reverted extracellular N-CAD, CLU, and HSP27 to levels similar to those in the control. These results constitute the first evidence that SPARC, N-CAD, CLU, and HSP27 converge in a unique molecular network in melanoma cells.

Cell interaction with the extracellular matrix (ECM) has profound influence in cancer progression. The secreted protein, acidic and rich in cysteine (SPARC) a component of the ECM, impairs the proliferation of different cell types and modulates tumor cell aggressive features. This apparent paradox might result either from the biochemical properties of the different SPARC sources or from differential responses of malignant and stromal cells to SPARC. To test these hypotheses, we purified SPARC secreted by melanoma cells (hMel-SPARC) and compared its activity with different recombinant SPARC preparations, including a new one produced in insect cells. All 5 SPARC species were effective in inhibiting bovine aortic endothelial cell proliferation, adhesion and migration. We then used the melanoma-derived protein to assess SPARC effect on additional cell types. hMel-SPARC greatly impaired the proliferation of both normal and transformed human endothelial cells and exerted a moderate biphasic effect on human fetal fibroblasts proliferation, irrespective of their endogenous SPARC levels. However, SPARC had no effect on the proliferation of several human cancer cell lines regardless of their endogenous levels of SPARC expression. Importantly, downregulation of SPARC levels in melanoma cells using either an antisense RNA or a shRNA against SPARC sensitized them to hMel-SPARC addition in proliferation and migration assays, suggesting that malignant cells developed a SPARC-resistance mechanism. This was not a general resistance to growth suppressing agents, as melanoma cells with restricted SPARC expression were more resistant to chemotherapeutic agents. Thus, malignant cells expressing or not expressing SPARC developed alternative mechanisms that, in contrary to stromal cells, rendered them SPARC-insensitive. ' 2007 Wiley-Liss, Inc.Key words: SPARC; osteonectin; cell proliferation; tumor heterogeneity; stromal cells Tumors grow as the result of crosstalk between the different cellular components of the tumor mass. Malignant cells secrete proteins that reach neighboring stromal nonmalignant cells (i.e., fibroblasts and endothelial cells) that in some cases induce them to provide the soil in which the tumor will grow.1 Nonmalignant stromal cells might also contribute to cancer progression, since the establishment of human cancer xenografts in mice depends on the presence of tumor-derived fibroblasts.2 This data therefore points toward a central role of extracellular matrix (ECM) in tumor progression.From the many proteins secreted by tumor and stromal cells, the secreted protein, acidic and rich in cysteine, SPARC (also known as BM40 and osteonectin), a nonstructural, matricellular component of the ECM, has been associated with tumor growth. In healthy tissues, SPARC production is largely restricted to areas undergoing repair or remodeling.4 SPARC is expressed at high levels in many tumors, and it was found to be associated with tumor progression in human melanoma, 5 properties on certain cell types have been associated with...