Endothelial expression of the α6β4 integrin is negatively regulated during angiogenesis

Abstract

Development and homeostasis of the vascular system requires integrin-facilitated cellular adhesion, migration, proliferation and survival. A specific role for the α6β4 integrin in the vasculature, however, has not been identified. Using immunohistochemistry, we observed α6β4 expression on the dermal microvasculature of human foreskin. Analysis of individual cells isolated from trypsin-disrupted foreskin tissue indicated that α6β4 was expressed by a subset of epithelial and endothelial cells, and not by smooth muscle cells. Expression of α6β4 was also analyzed during new vessel growth using explants of human saphenous vein cultured in fibrinogen gels. The results indicate that α6β4 is not expressed by outgrowing endothelial cells, and is downregulated by the original α6β4-positive endothelial cells of the explant. To determine whether α6β4 is expressed during angiogenesis in vivo, the expression of the β4 subunit was analyzed during the development of the mouse mystacial (whisker) pad. Immunohistochemical staining of the whisker pad indicates that β4 is expressed by the adult vasculature. To identify when and where β4 is turned on in the vasculature, we examined the whisker pads from the developing embryo (E19.5 pc), and from postnatal days zero (P0), three (P3) and seven (P7) pups. The expression of α6β4 was found to be turned on spatially and temporally from caudal to rostral regions and from the deep to superficial vasculature, correlating with the maturation of the whisker pad and its corresponding vasculature. Together, these findings suggest a potential role for α6β4 as a negative component of the angiogenic switch, whereas expression of α6β4 on the adult vasculature may indicate regions requiring additional adhesive mechanisms.

Endothelial α3β1-Integrin Represses Pathological Angiogenesis and Sustains Endothelial-VEGF

“…␣6-integrin subunits can heterodimerize with either ␤1-or ␤4-integrin subunits, both of which have been implicated in angiogenesis, [53][54][55] suggesting that the up-regulation of ␣6-integrins could account for the enhanced angiogenic responses found in ec-␣3Ϫ/Ϫ mice. In contrast we have shown recently that ␣6 integrin deletion can enhance angiogenesis.…”

Upregulation and redistribution of integrin α6β4 expression occurs at an early stage in pancreatic adenocarcinoma progression

“…As an internal positive control, we used staining of the integrin b4 subunit associated with endothelial cells (Figure 2b, asterisks), and Schwann cells in the peripheral nerves (Figure 1h) which have been reported to express this integrin previously. 22,23 The ductal epithelial cells of these normal pancreatic tissues (97%, n ¼ 39) showed expression of integrin a6b4 where it preferentially localized at the cellular interface with the basement membrane (Figures 1b and 2b). Interestingly, the cells within the pancreatic acini did not display any immunoreactivity for the b4 integrin subunit; however, cells localized at the base of the acinar epithelium stained positive for integrin a6b4.…”

“…PanINs were identified in one case of normal pancreas, 14 cases of chronic pancreatitis and 20 cases of pancreatic adenocarcinomas. Endothelial cells and cells in the peripheral nerves served as internal positive controls; 22,23 absence of staining in these cells was used as criteria to remove a sample from the study. Images were captured with a Nikon Digital Sight DS 5M color camera adapted to an upright Nikon Microscope Optiphot-2.…”

Genetic ablation of the alpha 6‐integrin subunit in Tie1Cre mice enhances tumour angiogenesis

“…However, since α6-integrin is overexpressed by several tumour cell types [46], the systemic administration of α6-integrin functionblocking antibodies would affect both the cancer cells and the endothelial cells in Lee et al's study, whereas our studies are restricted to the role of α6-integrin in endothelial cells. Hiran et al conversely showed that α6β4-integrin is down-regulated both in early vascular development of the murine whisker pad and during angiogenic sprouting in an ex vivo angiogenesis model [18], implicating α6β4-integrin as a negative regulator of angiogenesis. The apparent discrepancies between the various data, including ours, might be due to several reasons.…”

“…These data implied that down-regulation in α6β4-integrin was associated with the newly formed endothelial cells in both models. Thus, expression of the integrin may negatively regulate angiogenesis [18]. In contrast, mice generated to express a non-signalling β4-integrin subunit revealed that this globally expressed mutation reduced adult pathological angiogenesis.…”