Predictive Outcomes for HER2-enriched Cancer Using Growth and Metastasis Signatures Driven By SPARC

Understanding the mechanism of metastatic dissemination is crucial for the rational design of novel therapeutics. The secreted protein acidic and rich in cysteine (SPARC) is a matricellular glycoprotein which has been extensively associated with human breast cancer aggressiveness although the underlying mechanisms are still unclear. Here, shRNA-mediated SPARC knockdown greatly reduced primary tumor growth and completely abolished lung colonization of murine 4T1 and LM3 breast malignant cells implanted in syngeneic BALB/c mice. A comprehensive study including global transcriptomic analysis followed by biological validations confirmed that SPARC induces primary tumor growth by enhancing cell cycle and by promoting a COX-2-mediated expansion of myeloid-derived suppressor cells (MDSC). The role of SPARC in metastasis involved a COX-2-independent enhancement of cell disengagement from the primary tumor and adherence to the lungs that fostered metastasis implantation. Interestingly, SPARC-driven gene expression signatures obtained from these murine models predicted the clinical outcome of patients with HER2-enriched breast cancer subtypes. In total, the results reveal that SPARC and its downstream effectors are attractive targets for antimetastatic therapies in breast cancer.Implications: These findings shed light on the prometastatic role of SPARC, a key protein expressed by breast cancer cells and surrounding stroma, with important consequences for disease outcome. Mol Cancer Res; 15(3); 304-16. ©2016 AACR.

Abstract 4140: Secreted protein acidic and rich in cysteine (SPARC) promotes mammary tumor growth and dissemination through immune and non-immune mediated mechanisms

Secreted protein and rich in cysteine (SPARC) is a matricellular glycoprotein which has been extensively associated with breast cancer progression, both in human tumors and in experimental models. However, the molecular mechanisms responsible for this effect are still unclear in particular because most studies were performed in immunocompromised nude mice. We undertook a comprehensive study of SPARC role in this disease by using the highly metastatic and poorly immunogenic 4T1 and LM3 mammary tumor cells syngeneic in Balb/c mice. Knock down of SPARC expression using a targeted shRNA in both cell lines greatly reduced primary tumor growth and completely obliterated the establishment of metastatic foci in lung. We performed global gene expression analysis comparing primary tumors and metastatic foci of control 4T1 cells with those arisen from shRNA-treated, SPARC-deficient 4T1 cells. From these studies, a potential role of the inflammatory/immune response in controlling tumor evasion and metastasis, more specifically through genes associated with the prostaglandin pathway, was suggested. As we explored this hypothesis, we observed that knock down of SPARC expression in 4T1 3D spheroids, but not in 2D monolayers, downregulated COX-2 mRNA and protein levels. Moreover, exogenous addition of SPARC in SPARC-deficient spheroids of 4T1 and MDA-MB-231 human breast cancer cells increased COX-2 expression. Interestingly, the re-expression of COX-2 in SPARC-deficient 4T1 cells partially restored the in vivo primary tumor growth with no effect on the establishment of metastatic foci. COX-2 plays an important role in inducing myeloid-derived suppressor cells (MDSCs, CD11b+Gr-1+ cells), which promotes breast cancer outgrowth through immunosuppression. Flow cytometry analyses demonstrated that SPARC-deficient 4T1 tumor-bearing mice exhibited reduced levels of CD11b+Gr-1+ cells compared to control 4T1 tumor-bearing mice in the spleen (6,9±3,2 vs. 25,3±2,0 p<0,001), lungs (0,7±0,2 vs. 6,2±0,9 p<0,001) and bone marrow (48,0±6,4% vs. 62,1±5,3 p>0,05). COX-2 re-expression restored systemic MDSCs expansion in SPARC-deficient 4T1 tumor-bearing mice. The present data suggest that COX-2 expression is under SPARC control in breast cancer cells; moreover, COX-2 could mediate SPARC effects on tumor evasion from immune surveillance.

Citation Format: Leandro N. Güttlein, Lorena G. Benedetti, Raúl G. Spallanzani, Cecilia Rotondaro, Ximena L. Raffo Iraolagoitia, Leonardo Sganga, Edgardo Salvatierra, Andrea S. Llera, Norberto W. Zwirner, Osvaldo L. Podhajcer. Secreted protein acidic and rich in cysteine (SPARC) promotes mammary tumor growth and dissemination through immune and non-immune mediated mechanisms. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4140.

Redox modulation of plant developmental regulators from the class I TCP transcription factor family

TEOSINTE BRANCHED1-CYCLOIDEA-PROLIFERATING CELL FACTOR1 (TCP) transcription factors participate in plant developmental processes associated with cell proliferation and growth. Most members of class I, one of the two classes that compose the family, have a conserved cysteine at position 20 (Cys-20) of the TCP DNA-binding and dimerization domain. We show that Arabidopsis (Arabidopsis thaliana) class I proteins with Cys-20 are sensitive to redox conditions, since their DNA-binding activity is inhibited after incubation with the oxidants diamide, oxidized glutathione, or hydrogen peroxide or with nitric oxide-producing agents. Inhibition can be reversed by treatment with the reductants dithiothreitol or reduced glutathione or by incubation with the thioredoxin/thioredoxin reductase system. Mutation of Cys-20 in the class I protein TCP15 abolished its redox sensitivity. Under oxidizing conditions, covalently linked dimers were formed, suggesting that inactivation is associated with the formation of intermolecular disulfide bonds. Inhibition of class I TCP protein activity was also observed in vivo, in yeast (Saccharomyces cerevisiae) cells expressing TCP proteins and in plants after treatment with redox agents. This inhibition was correlated with modifications in the expression of the downstream CUC1 gene in plants. Modeling studies indicated that Cys-20 is located at the dimer interface near the DNA-binding surface. This places this residue in the correct orientation for intermolecular disulfide bond formation and explains the sensitivity of DNA binding to the oxidation of Cys-20. The redox properties of Cys-20 and the observed effects of cellular redox agents both in vitro and in vivo suggest that class I TCP protein action is under redox control in plants.