Arsenic-induced PML targeting onto nuclear bodies: Implications for the treatment of acute promyelocytic leukemia

Abstract

Acute promyelocytic leukemia (APL) is associated with the t(15;17) translocation, which generates a PML͞RAR␣ fusion protein between PML, a growth suppressor localized on nuclear matrix-associated bodies, and RAR␣, a nuclear receptor for retinoic acid (RA). PML͞RAR␣ was proposed to block myeloid differentiation through inhibition of nuclear receptor response, as does a dominant negative RAR␣ mutant. In addition, in APL cells, PML͞RAR␣ displaces PML and other nuclear body (NB) antigens onto nuclear microspeckles, likely resulting in the loss of PML and͞or NB functions. RA leads to clinical remissions through induction of terminal differentiation, for which the respective contributions of RAR␣ (or PML͞RAR␣) activation, PML͞ RAR␣ degradation, and restoration of NB antigens localization are poorly determined. Arsenic trioxide also leads to remissions in APL patients, presumably through induction of apoptosis. We demonstrate that in non-APL cells, arsenic recruits the nucleoplasmic form of several NB antigens onto NB, but induces the degradation of PML only, identifying a powerful tool to approach NB function. In APL cells, arsenic targets PML and PML͞RAR␣ onto NB and induces their degradation. Thus, RA and arsenic target RAR␣ and PML, respectively, but both induce the degradation of the PML͞ RAR␣ fusion protein, which should contribute to their therapeutic effects. The difference in the cellular events triggered by these two agents likely stems from RA-induced transcriptional activation and arsenic effects on NB proteins.

Retinoic acid, but not arsenic trioxide, degrades the PLZF/RARα fusion protein, without inducing terminal differentiation or apoptosis, in a RA-therapy resistant t(11;17)(q23;q21) APL patient

“…Similarly, As 2 O 3 had no obvious e ect on di erentiation or apoptosis. This is not surprising, taken into account the speci®c targeting of PML by As 2 O 3 and the absence of apparent direct interaction between PML and PLZF/ RARa Zhu et al, 1997). Nevertheless, in the patient's cells, the fusion product, PLZF/RARa, is speci®cally degraded by retinoic acid, consistent with our previous observation in transfected cells .…”

“…CBB represents a segment of the Coomassie Brilliant Blue stained gel to serve as loading control monocytic di erentiation in culture. This differentiation might result from the degradation of the chimeric protein, similar to that observed in NB4 cells where 10 77 M arsenic trioxide degrades PML/RARa and triggers a partial di erentiation (Chen et al, 1997a;Zhu et al, 1997).…”

The induction of apoptosis and cell cycle arrest by arsenic trioxide in lymphoid neoplasms

“…Thus, RA and arsenic seem to target RAR␣ and PML, respectively, and induce the degradation of the fusion protein. 21 These findings suggest that As 2 O 3 induces apoptosis most effectively in NB4 and APL cells which express PML/RAR␣ fusion protein.…”

“…The mechanism of PML/RAR␣ degradation by all-trans retinoic acid (RA) and As 2 O 3 are likely different. 21 With RA, a specific cleavage product of the fusion is generated that may retain some transcriptional activation properties. Thus, RA and arsenic seem to target RAR␣ and PML, respectively, and induce the degradation of the fusion protein.…”

PML enhances the regulation of p53 by CK1 in response to DNA damage

“…These cells express one allele of wild-type (wt) PML and one allele of oncogenic fusion PML-retinoic acid receptor a. The function of the wt PML is inactivated by the dominant negative fusion protein, but it can be restored by the treatment of NB4 cells with arsenic trioxide (As 2 O 3 ), which promotes PML-retinoic acid receptor a degradation and activation of the wt allele, resulting in the re-formation of PML-NBs ( Figure 2b); (Zhu et al, 1997;Muller et al, 1998). NB4 cells express mutant p53 (A248G; Rizzo et al, 1998), whose expression levels remain largely unchanged following exposure to stress.…”