Downregulation of a newly identified laminin, laminin-3B11, in vascular basement membranes of invasive human breast cancers.

Laminins present in the basement membranes (BM) of blood vessels are involved in angiogenesis and other vascular functions that are critical for tumor growth and metastasis. Two major vascular laminins, the α4 (laminin-411/421) and α5 (laminin-511/521) types, have been well characterized. We recently found a third type of vascular laminin, laminin-3B11, consisting of the α3B, ß1 and γ1 chains, and revealed its biological activity. Laminin-3B11 potently stimulates vascular endothelial cells to extend lamellipodial protrusions. To understand the roles of laminin-3B11 in blood vessel functions and tumor growth, we examined localization of the laminin α3B chain in normal mammary glands and breast cancers, in comparison with the α4 and α5 laminins. In the immunohistochemical analysis, the α3B laminin was co-localized with the α4 and α5 laminins in the BM of venules and capillaries of normal breast tissues, but α3B was scarcely detected in vessels near invasive breast carcinoma cells. In contrast, the α4 laminin was overexpressed in capillaries of invasive carcinomas, where a large number of macrophages were found. The α5 laminin appeared to be weakly downregulated in cancer tissues, especially in capillary vessels. Furthermore, our in vitro analysis indicated that TNF-α significantly suppressed the laminin α3B expression in vascular endothelial cells, while it, as well as IL-1ß and TGF-α, upregulated the α4 expression. These results suggest that Lm3B11/3B21 may be required for normal mature vessels and interfere with tumor angiogenesis.