DAPL1, a susceptibility locus for age-related macular degeneration, acts as a novel suppressor of cell proliferation in the retinal pigment epithelium

Abstract

The retinal pigment epithelium (RPE) forms a monolayer at the back of the vertebrate eye and is fundamental to retinal function and homoeostasis. During early development, RPE cells undergo rapid proliferation, but in the adult, they remain normally nonproliferative throughout life. Nevertheless, under pathological conditions such as in proliferative vitreoretinopathy or after retinal ablation, mature RPE cells can re-enter the cell cycle and form nodules or multiple cell layers. Here we show that Dapl1, whose human homolog represents a susceptibility locus for age-related macular degeneration (AMD), is highly up-regulated in quiescent but not proliferating RPE cells and that experimental overexpression of DAPL1 in proliferating RPE cells inhibits their proliferation. Consistent with this observation, the percent of Ki67-positive cells is significantly higher in E11.5 Dapl1 knockout mouse embryos compared to age-matched controls. In adult Dapl1-/- mice, which survive without showing any overt pathology, RPE overgrowth leads to multiple cell layers and/or cellular nodules. The antiproliferative effect of DAPL1 is associated with an increase in CDKN1A protein levels. Reduction of CDKN1A by siRNA in DAPL1-overexpressing RPE cells in vitro partially restores cell proliferation. Hence, we show that DAPL1 is a novel regulator of RPE cell proliferation that is important for the maintenance of the RPE as a monolayer. The findings suggest that DAPL1 dysregulation may be involved in abnormal RPE-related proliferative diseases and corresponding retinal dysfunctions in humans.

Regulation of cell proliferation in the retinal pigment epithelium: Differential regulation of the death‐associated protein like‐1 DAPL1 by alternative MITF splice forms

“…Our previous work has demonstrated that DAPL1 plays a critical role in inhibiting RPE cell proliferation both in vitro and in vivo (Ma et al., ). Confirming these results, the presence of Ki67‐positive cells was dramatically decreased in DAPL1 overexpressing ARPE‐19 cells (ARPE19 + DAPL1) compared with EGFP‐overexpressing control cells (Figure a,b).…”

“…Transfection with either si‐RNAs led to a partial rescue of cell proliferation (Figure c–e). Our previous work has demonstrated that DAPL1 inhibits RPE cell proliferation in part by increasing the protein levels of P21, which can downregulate the levels of p‐RB, P107, and E2F1 (Ma et al., ). To investigate whether DAPL1 mediates (−) MITF‐induced ARPE‐19 cell proliferation inhibition through the P21‐p‐RB, P107, and E2F1 axis, we analyzed the levels of these proteins in (−) MITF‐infected cells with or without knockdown of DAPL1.…”

“…Interestingly, based on the analysis of genetic polymorphisms, DAPL1 has also been described as a female‐specific susceptibility locus for age‐related macular degeneration (AMD) (Grassmann et al., ), which is thought to result from a regional degeneration of the RPE that is incapable of regenerative proliferation. In fact, we previously found DAPL1 to be highly expressed in mature RPE cells and to inhibit RPE proliferation, based on in vitro experiments and on the observation that in Dapl1 knockout mice, the RPE hyperproliferates, leading to multiple cell layers and/or cellular nodules (Ma et al., ). Here, we explore in vitro how DAPL1 is regulated in normal RPE cells.…”

WITHDRAWN: Identification of death-associated protein-like 1 (DAPL1) as a novel prognostic biomarker of breast cancer

“…The death-associated protein-like 1 (DAPL1) protein, encoded by DAPL1 gene, was reported to be associated with the pathogenesis of age-related macular degeneration (AMD) [2] and the regulation of cell proliferation in the retinal pigment epithelium (RPE) [3,4]. A whole genome expression profiling data suggested that DAPL1 gene may be linked to the chewing-tobacco-associated oral cancer [5].…”

Nf2 fine-tunes proliferation and tissue alignment during closure of the optic fissure in the embryonic mouse eye

“…This is consistent with the inability of the RPE to renew itself, once differentiation and further maturation commences (112). Few factors have been identified that can promote proliferation and expansion of RPE; these include transgenic hyperactivation of Notch signaling, resulting in microphthalmia and coloboma (29,113), or loss of factors that normally limit proliferation in the developing RPE, such as the cyclin-dependent kinase inhibitor p27Kip1 or DAPL1 (114)(115)(116). Collectively, our analysis reveals a unique role for Nf2 in regulating closure of the optic fissure by restricting RPE proliferation in the optic cup.…”