Degradation of soluble VEGF receptor-1 by MMP-7 allows VEGF access to endothelial cells.

Vascular endothelial growth factor (VEGF) signaling in endothelial cells serves a critical role in physiologic and pathologic angiogenesis. Endothelial cells secrete soluble VEGF receptor-1 (sVEGFR-1/sFlt-1), an endogenous VEGF inhibitor that sequesters VEGF and blocks its access to VEGF receptors. This raises the question of how VEGF passes through this endogenous VEGF trap to reach its membrane receptors on endothelial cells, a step required for VEGF-driven angiogenesis. Here, we show that matrix metalloproteinase-7 (MMP-7) degrades human sVEGFR-1, which increases VEGF bioavailability around the endothelial cells. Using a tube formation assay, migration assay, and coimmunoprecipitation assay with human umbilical vein endothelial cells (HUVECs), we show that the degradation of sVEGFR-1 by MMP-7 liberates the VEGF(165) isoform from sVEGFR-1. The presence of MMP-7 abrogates the inhibitory effect of sVEGFR-1 on VEGF-induced phosphorylation of VEGF receptor-2 on HUVECs. These data suggest that VEGF escapes the sequestration by endothelial sVEGFR-1 and promotes angiogenesis in the presence of MMP-7.

CD105-positive cells in pulmonary arterial blood of adult human lung cancer patients include mesenchymal progenitors.

Mesenchymal progenitor cells (MPCs) exhibit fibroblast-like morphology and are multipotent cells capable of differentiating into various mesenchymal tissues. Although MPCs have been found in adult bone marrow and umbilical cord blood, there is still controversy as to whether the MPCs are present in adult human blood. To determine whether they are, we cultured mononuclear cells (MNCs) from the pulmonary arterial blood of lung cancer patients. In 94% (29 of 31) of the cases, fibroblasts were expanded ex vivo and were differentiated into an osteogenic lineage or an adipogenic lineage, depending on the specific inducing medium used. These results indicated that pulmonary arterial blood (PA) in the vicinity of lung cancers contains MPCs (PA-MPCs). The cDNA profiles of PA-MPCs, MPCs derived from bone marrow (BM-MPCs), and lung tissue-derived fibroblasts were clustered with a hierarchical classification algorithm. The expression profiles of PA-MPCs (three cases) and BM-MPCs were clearly separated from those of the tissue-derived fibroblasts, and the profiles of the PA-MPCs from the two patients were separated from those of the BM-MPCs. To identify the source of the PA-MPCs, the MNCs from pulmonary arterial blood were exposed to anti-CD14, anti-CD105, anti-CD3, and anti-CD20 antibodies. CD105(+) MNCs generated MPCs in eight of eight cases (100%), whereas CD14(+), CD3(+), and CD20(+) mononuclear cells generated MPCs in three of five cases (60%), two of five cases (40%), and zero of three cases (0%), respectively. These findings are the first clear proof that the CD105(+) MNC fraction in the pulmonary arterial blood of adult lung cancer patients includes MPCs. Disclosure of potential conflicts of interest is found at the end of this article.

Presence of human circulating progenitor cells for cancer stromal fibroblasts in the blood of lung cancer patients.

Recent animal data have suggested that cancer-induced stroma consists of blood-borne fibroblasts as well as tissue-derived fibroblasts. In this study, mononuclear cells isolated from the pulmonary vein blood of lungs resected from lung cancer patients were cultured to confirm the presence of blood-borne fibroblast. In 34% (16 of 47) of the cases, spindle cells with fibroblast morphology proliferated in a disarrayed fashion and were positive for vimentin and collagen type I but negative for both specific myogenic and endothelial markers. The cDNA profiles of blood-borne fibroblasts, tissue-derived (lung) fibroblasts, human vascular smooth muscle cells (HSMCs), and umbilical vein endothelial cells (HUVECs) were clustered with a hierarchical classification algorithm. The profiles of the blood-borne fibroblasts were clearly isolated from those of the tissue-derived fibroblasts, HSMCs, and HUVECs. When carboxyfluorescein succinyl ester (CFSE)-labeled human mononuclear cells from the blood of lung cancer patients were transferred into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice engrafted with a human lung cancer xenograft, CFSE-labeled fibroblasts were found around the cancer nests. We investigated the several clinicopathological factors of blood-borne fibroblast-positive patients. The blood-borne fibroblast-positive cases had a significantly larger central fibrotic area in primary lung cancer than in the negative cases (123 +/- 29 vs. 59 +/- 13 mm(2); p = .02). Our results indicated that the blood in the vicinity of human lung cancer contains fibroblast progenitor cells that have the capacity to migrate into the cancer stroma and differentiate into fibroblasts having biological characteristics different from those of tissue-derived fibroblasts. Disclosure of potential conflicts of interest is found at the end of this article.