Retinoic Acid Increases the Expression of p53 and Proapoptotic Caspases and Sensitizes Keratinocytes to Apoptosis

Abstract

Retinoids influence growth and differentiation of keratinocytes (KCs) and are widely used for the management of skin diseases and for prevention of nonmelanoma skin cancer (NMSC) in predisposed patients. Here we investigated the effect of all-trans-retinoic acid (ATRA) on KC apoptosis. When KCs were cultured in confluent monolayers for several days, they acquired resistance against UVB-induced apoptosis. In contrast, when the cells were treated with 1 mol/L ATRA for 6 days and subsequently irradiated with different doses of UVB, they underwent massive apoptosis as assessed by morphology, expression of activated caspase-3, and DNA fragmentation. The same effect was observed when doxorubicin was used instead of UVB. Analysis by real-time PCR and Western blot revealed that ATRA treatment strongly increased the mRNA and protein expression of p53 and caspase-3, -6, -7, and -9, which are key regulators of apoptosis. UVB irradiation of ATRA-treated cells but not of control cells led to the accumulation of p53 protein and of its target gene Noxa. Inhibition of p53 and caspases with ␣-pifithrin and z-Val-Ala-Aspfluoromethyl ketone, respectively, blocked UVB-and doxorubicin-induced apoptosis in ATRA-treated KCs. Analogous to the observed ATRA effects in monolayer cultures, in vitro-generated organotypic skin cultures reacted with up-regulation of p53 and proapoptotic caspases and displayed increased sensitivity to UVB-induced apoptosis. The ability of retinoic acid to regulate the expression of proapoptotic genes and to sensitize KCs to apoptosis may play a role in their prevention of NMSC in transplant patients and patients with DNA-repair deficiencies.

Suppression of Mammary Carcinoma Growth by Retinoic Acid: Proapoptotic Genes Are Targets for Retinoic Acid Receptor and Cellular Retinoic Acid–Binding Protein II Signaling

“…In keratinocytes, RA treatment was reported to upregulate the expression of several caspases. The mechanism by which RA increases caspase expression in these cells remains unknown, but it has been shown that although their overexpression does not induce apoptosis by itself, it sensitizes the cells to apoptosis induced by UVB irradiation and by doxorubicin (36). We show here that in MCF-7 cells, RA increases the expression of several proapoptotic genes and leads to pronounced apoptosis without the need for additional agents.…”

Retinoic Acid/Alpha-Interferon Combination Inhibits Growth and Promotes Apoptosis in Mantle Cell Lymphoma through Akt-Dependent Modulation of Critical Targets

“…Indeed, RA/IFN combination was previously shown to exert synergistic antiproliferative and proapoptotic effects in different cancer cell systems (11,12). With particular regard to the proapoptotic activity, these compounds can variably promote both the downregulation of antiapoptotic proteins such as Bcl-2, Bcl-xL, and Mcl-1 (12,13), often overexpressed in B-NHLs, including MCL (14)(15)(16)(17)(18) and/or the induction of proapoptotic proteins, including Bax, Noxa, and XAF1 (12,(19)(20)(21)(22)(23).…”

Evidence for a specific cell membrane retinol-binding protein transport mechanism in a human keratinocyte line

“…[1][2][3][4]. These effects are critical for maintaining skin health and suppressing carcinogenesis in skin (1,2,(4)(5)(6). Despite extensive knowledge of various retinoid-dependent gene expression effects in epidermal and other cell types, however, much less is known about retinoid transport events at the cell membrane; and endocytosis of circulatory vitamin A carrier proteins by epidermal cells or epidermoid cancer cells remains poorly understood and controversial (see below).…”