Abstract
Dysregulation in the extracellular matrix (ECM) microenvironment surrounding the retinal pigment epithelium (RPE) has been implicated in the etiology of proliferative vitreoretinopathy and age-related macular degeneration. The regulation of ECM remodeling by RPE cells is not well understood. We show that membrane-type matrix metalloproteinase 14 (MMP14) is central to ECM degradation at the focal adhesions in human ARPE19 cells. The matrix degradative activity, but not the assembly, of the focal adhesion is regulated by chloride intracellular channel 4 (CLIC4). CLIC4 is co-localized with MMP14 in the late endosome. CLIC4 regulates the proper sorting of MMP14 into the lumen of the late endosome and its proteolytic activation in lipid rafts. CLIC4 has the newly-identified “late domain” motif that binds to MMP14 and to Tsg101, a component of the endosomal sorting complex required for transport (ESCRT) complex. Unlike the late domain mutant CLIC4, wild-type CLIC4 can rescue the late endosomal sorting defect of MMP14. Finally, CLIC4 knockdown inhibits the apical secretion of MMP2 in polarized human RPE monolayers. These results, taken together, demonstrate that CLIC4 is a novel matrix microenvironment modulator and a novel regulator for late endosomal cargo sorting. Moreover, the late endosomal sorting of MMP14 actively regulates its surface activation in RPE cells.
Highlights
The extracellular matrix (ECM) is a highly dynamic structure that continuously undergoes regulated remodeling[1]
This paper makes several advances in our understanding of ECM remodeling and the endosomal trafficking of retinal pigment epithelium (RPE) cells. (i) Here we investigated the dynamic pericellular gelatin degradation function of ARPE19 cells
These studies complemented the previous reports which used zymography for the secreted gelatinase activity[42,43,44] and the structural characterization of the ECM formed underneath the long-term ARPE19 cultures46. (ii) Our studies show that in ARPE19 cells matrix metalloproteinase 14 (MMP14) is central to the genesis of the degradation foci at the focal adhesions
Summary
The extracellular matrix (ECM) is a highly dynamic structure that continuously undergoes regulated remodeling[1]. Cancer cell studies showed that the surface expression of MMP14 is highly dynamic and regulated through the endocytic trafficking pathway involving the late endosome (LE)[20,21,22]. The expression of CLIC4 is susceptible to environmental changes (e.g., oxidative stress, transforming growth factors, lipopolysaccharide, nitric oxide) that are known to modulate the expression level of MMP1430–37 These coincidences prompted us to investigate the putative relationship between CLIC4 and MMP14 in retinal pigment epithelium (RPE) cells. MMP14 and CLIC4 both have an important role in the dynamic ECM remodeling of the ARPE19 cells. Corroborating with CLIC4’s role in regulating the ECM remodeling, we demonstrated that in polarized human RPE monolayers, the secretion of MMP2 was significantly reduced when CLIC4 was suppressed
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