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Articles by R. A. Brekken
Total Records ( 2 ) for R. A. Brekken
  S. A Arnold , L. B Rivera , A. F Miller , J. G Carbon , S. P Dineen , Y Xie , D. H Castrillon , E. H Sage , P Puolakkainen , A. D Bradshaw and R. A. Brekken
  Shanna A. Arnold, Lee B. Rivera, Andrew F. Miller, Juliet G. Carbon, Sean P. Dineen, Yang Xie, Diego H. Castrillon, E. Helene Sage, Pauli Puolakkainen, Amy D. Bradshaw, and Rolf A. Brekken

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.

  M. K Schluterman , S. L Chapman , G Korpanty , K Ozumi , T Fukai , H Yanagisawa and R. A. Brekken
  Marie K. Schluterman, Shelby L. Chapman, Grzegorz Korpanty, Kiyoshi Ozumi, Tohru Fukai, Hiromi Yanagisawa, and Rolf A. Brekken

Tumor survival depends in part on the ability of tumor cells to transform the surrounding extracellular matrix (ECM) into an environment conducive to tumor progression. Matricellular proteins are secreted into the ECM and impact signaling pathways that are required for pro-tumorigenic activities such as angiogenesis. Fibulin-5 (Fbln5) is a matricellular protein that was recently shown to regulate angiogenesis; however, its effect on tumor angiogenesis and thus tumor growth is currently unknown. We report that the growth of pancreatic tumors and tumor angiogenesis is suppressed in Fbln5-null (Fbln5–/–) mice compared with wild-type (WT) littermates. Furthermore, we observed an increase in the level of reactive oxygen species (ROS) in tumors grown in Fbln5–/– animals. Increased ROS resulted in elevated DNA damage, increased apoptosis of endothelial cells within the tumor, and represented the underlying cause for the reduction in angiogenesis and tumor growth. In vitro, we identified a novel pathway by which Fbln5 controls ROS production through a mechanism that is dependent on β1 integrins. These results were validated in Fbln5RGE/RGE mice, which harbor a point mutation in the integrin-binding RGD motif of Fbln5, preventing its interaction with integrins. Tumor growth and angiogenesis was reduced in Fbln5RGE/RGE mice, however treatment with an antioxidant rescued angiogenesis and elevated tumor growth to WT levels. These findings introduce a novel function for Fbln5 in the regulation of integrin-induced ROS production and establish a rationale for future studies to examine whether blocking Fbln5 function could be an effective anti-tumor strategy, alone or in combination with other therapies.

 
 
 
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