Arsenic Sulfide Promotes Apoptosis in Retinoid Acid Resistant Human Acute Promyelocytic Leukemic NB4-R1 Cells through Downregulation of SET Protein

Abstract

Tetra-arsenic tetra-sulfide (As4S4) is an arsenic compound with anti-tumor activity, especially in acute promyelocytic leukemia (APL) that are resistant to retinoic acid (RA). Although recent studies revealed that the therapeutic action of As4S4 is closely associated with the induction of cellular apoptosis, the exact molecular mechanism of action of As4S4 in RA-resistant APL remains to be clarified. In this study, we found that As4S4-induced apoptosis was accompanied by reduced mRNA and protein expression of SET gene in RA-resistant NB4-R1 cells. Moreover, RNAi knockdown of SET gene further promoted As4S4-induced apoptosis, while SET over-expression inhibited it, suggesting that As4S4 induces apoptosis through the reduction of SET protein in NB4-R1 cells. We also demonstrated that the knockdown of SET gene resulted in the upregulation of protein phosphatase 2 (PP2A) expression and the downregulation of promyelocytic leukemia and retinoic acid receptor α fusion gene (PML-RARα) expression, which were enhanced by As4S4 treatments. By contrast, over-expression of SET gene resulted in PP2A downregulation and PML-RARα upregulation, which were abolished by As4S4 pretreatment. Since PP2A is a pro-apoptotic factor and PMLRARα is an anti-apoptotic factor, our results suggest that As4S4-induced apoptosis in NB4-R1 cells is through the downregulation of SET protein expression, which in turn increases PP2A and reduces PML-RARα expressions to lead to cell apoptosis.

Arsenic sulfide, the main component of realgar, a traditional Chinese medicine, induces apoptosis of gastric cancer cells in vitro and in vivo

“…As 4 S 4 , an arsenic compound, has shown antitumor activities in malignancies, especially in APL, with limited toxicities. 14 – 18 The molecular mechanism of its antitumor activity is related to its ability to induce apoptosis 19 , 21 , 34 , 35 and the redistribution of PML-RARα protein in the leukemic cells. 20 …”

Oral Realgar-Indigo Naturalis Formula Treatment for Acute Promyelocytic Leukemia in Children: A Randomized, Control Clinical Trial

“…e efficacy of RIF in APL is not inferior to that of ATO due to its unique mechanism. As4S4, which is the main active ingredient of realgar in RIF, can induce apoptosis in HL-60 and NB4-R1 cells [36][37][38][39]. Wang and Liu et al demonstrated that As4S4 could significantly induce the degradation of the PML-RARα oncoprotein in mouse models and in vitro experiments.…”

Perspective on Therapeutic Strategies of Leukemia Treatment — Focus on Arsenic Compounds

“…It is no doubt that PML-RARα plays a central role in the initiation of leukemogenesis, although there is evidence to suggest that the fusion gene expression is not the sole genetic event required for the development of APL [4][5][6]. It has been clarified that arsenic-mediated modulation/degradation of the PML-RARα oncoprotein is one of the major mechanisms responsible for the efficacy of arsenic compounds in APL [4][5][6]93]. Furthermore, the PML moiety, but not the RARα moiety, of the PML-RARα chimera represents the target for arsenic treatment [6,61].…”

“…It has been clarified that both PML and PML-RARα form high-molecularweight conjugates with a small ubiquitin-related modifier (SUMO)-1 and are recruited from the nucleoplasm to the nuclear body (NB), followed by ubiquitin-mediated proteolysis [94][95][96]. Degradation of PML-RARα is closely associated with differentiation, growth inhibition associated with the induction of apoptosis, as well as cell cycle arrest in APL cells treated with arsenic compounds [4][5][6]93]. In addition, degradation of the PML-RARα protein associated with its redistribution was also reported in fresh APL cells obtained from the PB and BM of APL patients after treatment with As 4 S 4 [97].…”

“…In addition, degradation of the PML-RARα protein associated with its redistribution was also reported in fresh APL cells obtained from the PB and BM of APL patients after treatment with As 4 S 4 [97]. More intriguingly, Tian and colleagues have recently investigated the effects of As 4 S 4 on RA-resistant human APL NB4-R1 cells and found that treatment with As 4 S 4 induced apoptosis in cells through the downregulation of expression of the SET gene, which is a natural inhibitor for protein phosphatase 2 (PP2A), a pro-apoptotic protein [93]. They further demonstrated that the addition of As 4 S 4 strengthened the SET RNAiinduced upregulation of PP2A and the downregulation of PML-RARα, suggesting that As 4 S 4 induces apoptosis through the downregulation of the SET protein expression, which, in turn, increases PP2A expression and reduces PML-RARα expression, consequently leading to the apoptosis of NB4-R1 cells [93].…”