BRAK/CXCL14 Is a Potent Inhibitor of Angiogenesis and a Chemotactic Factor for Immature Dendritic Cells

Abstract

BRAK/CXCL14 is a CXC chemokine constitutively expressed at the mRNA level in certain normal tissues but absent from many established tumor cell lines and human cancers. Although multiple investigators cloned BRAK, little is known regarding the physiologic function of BRAK or the reason for decreased expression in cancer. To understand the possible significance associated with loss of BRAK mRNA in tumors, we examined the pattern of BRAK protein expression in normal and tumor specimens from patients with squamous cell carcinoma (SCC) of the tongue and used recombinant BRAK (rBRAK) to investigate potential biological functions. Using a peptide-specific antiserum, abundant expression of BRAK protein was found in suprabasal layers of normal tongue mucosa but consistently was absent in tongue SCC. Consistent with previous in situ mRNA studies, BRAK protein also was expressed strongly by stromal cells adjacent to tumors. In the rat corneal micropocket assay, BRAK was a potent inhibitor of in vivo angiogenesis stimulated by multiple angiogenic factors, including interleukin 8, basic fibroblast growth factor, and vascular endothelial growth factor. In vitro, rBRAK blocked endothelial cell chemotaxis at concentrations as low as 1 nmol/L, suggesting this was a major mechanism for angiogenesis inhibition. Although only low affinity receptors for BRAK could be found on endothelial cells, human immature monocyte-derived dendritic cells (iDCs) bound rBRAK with high affinity (i.e., K d , ϳ2 nmol/L). Furthermore, rBRAK was chemotactic for iDCs at concentrations ranging from 1 to 10 nmol/L. Our findings support a hypothesis that loss of BRAK expression from tumors may facilitate neovascularization and possibly contributes to immunologic escape.

Murine CXCL14 Is Dispensable for Dendritic Cell Function and Localization within Peripheral Tissues

“…We were unable to detect alternative CXCL14-responsive cell types, such as LCs and DCs, or other cell lineages like T, B, and NK cells. Other laboratories reported a role for CXCL14 in the recruitment of DCs by showing chemotactic activity for immature DCs (44,46). At present we have no explanation for this obvious discrepancy between our findings and those of other groups.…”

“…As human CXCL14 was shown to be involved in monocyte and DC recruitment (19,42,44,46), these subsets were analyzed in more detail in blood, spleen, bone marrow, and peripheral lymph nodes ( Fig. 2A and B).…”

“…Besides their role in migration, certain chemokines are involved in angiogenesis, hematopoiesis, and organogenesis (14,22,37). As CXCL14 was shown to be absent from a variety of tumors, Shellenberger et al hypothesized that CXCL14 could be involved in the tumor-associated angiogenesis and could indeed demonstrate inhibition of angiogenesis by CXCL14 (44). Furthermore, activated macrophages release growth factors and cytokines, namely, platelet-derived growth factor, fibroblast growth factor 2, and transforming growth factor ␤1, as well as tumor necrosis factor ␣ and interleukin-1, that modulate tissue repair and angiogenesis (29).…”

“…Human CXCL14, alternatively called BRAK and MIP-2␥, is constitutively produced in healthy epithelial tissues such as skin and gut. CXCL14 is also present in various tumors of epithelial origin, but the level of expression is heterogeneous, with the majority showing a downregulation with respect to healthy tissue (4,9,15,19,43,44,46). Recently, we have shown that human CXCL14 is selective for blood monocytes and CD14 ϩ DC precursors, either derived from CD34 ϩ hematopoietic progenitor cells or isolated from blood (19,42).…”

Mesenchymal stem cell‐loaded cardiac patch promotes epicardial activation and repair of the infarcted myocardium

“…CXCL14 specifically binds to CXCR4 with high affinity and inhibits the CXCL12‐mediated cell migration 33. Moreover, CXCL14 is a potent inhibitor of angiogenesis 34. Decrease in CXCL14 expression in this study promotes migration of c‐kit + cells as well as angiogenesis.…”