Abstract
Integrins are a family of transmembrane glycoproteins that mediate cell-cell and cell-extracellular matrix interactions. The integrin α4 subunit is widely expressed by cells from the immune system and its expression by non-hematopoietic cells is scarce. In the present study, gene and protein expression of this integrin subunit was characterized in proliferating and quiescent human RPE cells. Immunofluorescent studies confirm that the α4 subunit is expressed in vitro by RPE cells, a result that has been validated by immunofluorescence and FACS analyses. The accumulation of the α4 integrin at cell-cell junctions in post-confluent RPE cell cultures negatively correlated with the level of expression of the mRNA transcript. Accordingly, transient transfection analyses reveal that the α4 promoter activity is considerably reduced when RPE cells form a confluent monolayer. Moreover, transfection of recombinant constructs bearing 5’-deletions of the α4 promoter segment allows the localization of strong negative regulatory elements on the -76 to -300 region of the α4 gene suggesting that its expression is intimately linked to the proliferative state of primary cultured RPE cells.
Highlights
The retinal pigment epithelium (RPE) is a monolayer of polarized cells that separates the retina from the underlying vasculature
RPE cells that were left for 2 weeks at confluency were tightly packed and showed a positive α4 staining at cell-cell contacts (Figure 2(C))
The expression of the α4 integrin subunit by RPE cells has been further demonstrated by FACS analyses that clearly confirm the expression of this protein in vitro (Figure 3)
Summary
The retinal pigment epithelium (RPE) is a monolayer of polarized cells that separates the retina from the underlying vasculature. The integrin α4β1 mediates both cell-cell and cell-ECM interactions and plays an important role in development and cell differentiation This integrin is expressed by a variety of hematopoietic cells including lymphocytes, monocytes and eosinophils [19]-[22]. It plays an important role in the regulation of the immune response by promoting the recruitment of lymphocytes at inflammation sites [23]-[25] by its interaction with VCAM-1 on activated vascular endothelial cells, allowing for diapedesis [26]. Knockout mice lacking α4 die at embryonic day 11 due to cardiac and placental formation failure [29] [39]
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