Pondering the Promyelocytic Leukemia Protein (PML) Puzzle: Possible Functions for PML Nuclear Bodies (original) (raw)

Pml nuclear body disruption cooperates in APL pathogenesis and impairs DNA damage repair pathways in mice

Blood, 2018

A hallmark of acute promyelocytic leukemia (APL) is altered nuclear architecture, with disruption of promyelocytic leukemia (PML) nuclear bodies (NBs) mediated by the PML-retinoic acid receptor α (RARα) oncoprotein. To address whether this phenomenon plays a role in disease pathogenesis, we generated a knock-in mouse model with NB disruption mediated by 2 point mutations (C62A/C65A) in the Pml RING domain. Although no leukemias developed in Pml mice, these transgenic mice also expressing RARα linked to a dimerization domain (p50-RARα model) exhibited a doubling in the rate of leukemia, with a reduced latency period. Additionally, we found that response to targeted therapy with all- retinoic acid in vivo was dependent on NB integrity. PML-RARα is recognized to be insufficient for development of APL, requiring acquisition of cooperating mutations. We therefore investigated whether NB disruption might be mutagenic. Compared with wild-type cells, primary Pml cells exhibited increased si...

Finding a role for PML in APL pathogenesis: a critical assessment of potential PML activities

Leukemia, 2002

In normal mammalian cells the promyelocytic leukemia protein (PML) is primarily localized in multiprotein nuclear complexes called PML nuclear bodies. However, both PML and PML nuclear bodies are disrupted in acute promyelocytic leukemia (APL). The treatment of APL patients with all-trans retinoic acid (ATRA) results in clinical remission associated with blast cell differentiation and reformation of the PML nuclear bodies. These observations imply that the structural integrity of the PML nuclear body is critically important for normal cellular functions. Indeed, PML protein is a negative growth regulator capable of causing growth arrest in the G 1 phase of the cell cycle, transformation suppression, senescence and apoptosis. These PML-mediated, physiological effects can be readily demonstrated. However, a discrete biochemical and molecular model of PML function has yet to be defined. Upon first assessment of the current PML literature there appears to be a seemingly endless list of potential PML partner proteins implicating PML in a variety of regulatory mechanisms at every level of gene expression. The purpose of this review is to simplify this confusing field of research by using strict criteria to deduce which models of PML body function are well supported.

The PML gene encodes a phosphoprotein associated with the nuclear matrix

Blood, 1995

The t(15;17)(q22;q12) translocation is the cytogenetic hallmark of acute promyelocytic leukemia (APL). The PML and retinoic acid receptor-& (RA&) transcription factor genes are involved at the translocation breakpoint. To elucidate the biologic function of PML, antipeptide antibody against PML protein was raised in rabbits. This antibody was able to detect a 90-kD PML protein and a 110-kD PML-RARa fusion protein by Western blotting and a nuclear speckled pattern in all cell lines by immunofluorescent staining. In K562 and NIH/3T3 cells transfected with a PML expression plasmid, we found PML to be associated with the nuclear matrix. Our results also showed that PML is a phosphoprotein. A weak signal was detected in a Western blot containing the immunoprecipitated PML protein using the phosphotyrosine-specific monoclonal antibody. Therefore, at least one of the sites B ECAUSE THE NONRANDOM chromosome translocation t(15; 17)(q22;q12) can be found in over 95% of patients with acute promyelocytic leukemia (APL),'.' one can infer that genes involved in this unique translocation event play a role in its pathogenesis. Studies from several laboratories have confirmed that the t(15; 17) translocation occurs within the zinc finger transcription factor gene, PML, and the retinoic acid receptor-a (RARa) gene."' Because an extremely high number of APL patients can be induced to complete clinical remission by all-trans retinoic acid (ATRA),'"' it is believed that disruption of the RARa gene by the translocation plays a role in the leukemogenesis. However, evidence indicates that, when the myeloid leukemia cell line HL-60 loses its RA inducibility, this inducibility can be completely restored by other forms of RAR or retinoic X receptor (RXR)," suggesting that the loss of RARa function by APL cells may not be a critical event in leukemogenesis. Recent reports showed that the fusion protein PML-RARa encoded from the t(15; 17) breakpoint is responsible for RA inducibility in APL, because transfection of the PML-RARa cDNA into the human myeloid leukemia cell line U937 conferred RA inducibility." Furthermore, APL-derived NB4 cells that lose their RA inducibility also lose expression of the PML-RARa protein."

PML protein association with specific nucleolar structures differs in normal, tumor and senescent human cells

Journal of Structural Biology, 2007

Promyelocytic leukemia protein (PML), a tumor suppressor, forms in most human cell types discrete multiprotein complexes termed PML nuclear bodies. Here, we have used indirect immunofluorescence and confocal microscopy to describe various forms of a novel nuclear PML compartment associated with nucleoli that is found under growth-permitting conditions in human mesenchymal stem cells (hMSC) and skin fibroblasts but not in several immortal cell lines with defects in the p53 and pRb pathways. In addition, we found that shut-off of rRNA synthesis induced by actinomycin D causes PML translocation to the surface of segregated nucleoli. This translocation is dynamic and reversible, following changes in nucleolar activity. Intriguingly, treatment causing premature senescence restores PML binding to nucleoli-derived structures and to the surface of segregated nucleoli in HeLa cells. These findings indicate that PML may be involved in nucleolar functions of normal non-transformed or senescent cells. The absence of nucleolar PML compartment in rapidly growing tumor-derived cells suggests that PML association with the nucleolus might be important for cell-cycle regulation.

Involvement of PML-I in reformation of PML nuclear bodies in acute promyelocytic leukemia cells by leptomycin B

Toxicology and Applied Pharmacology, 2019

Acute promyelocytic leukemia (APL) is characterized by a reciprocal translocation between chromosomes 15 and 17, t(15;17), resulting in the expression of PML-RARα fusion protein, which disrupts the normal PML nuclear bodies (PML-NBs) to micro-speckled pattern, leading to loss of their original functions. Moreover, reformation of PML-NBs in APL by arsenic is considered as one of the important step for APL treatment. Leptomycin B (LMB), a nuclear export inhibitor, is commonly used to inhibit the proteins exporting from the nucleus to the cytoplasm. In the present study, we found that LMB could induce the reformation of PML-NBs in leukemia NB4 cells as well as in APL blast cells from the patients, implying that nuclear shuttle proteins might be involved in the reformation of PML-NBs. Herein, we further found that LMB totally lost the ability to induce PML-NBs reformation when the endogenous PML gene was knocked out, indicating that endogenous PML protein is probably involved in the reformation of PML-NBs. More interestingly, among all PML isoforms (i.e., seven isoforms), reformation of PML-NBs was only observed when co-transfection of PML-RARα with PML-I after LMB treatment. Similarly, deletion of nuclear export signal (NES) of PML-I could also reform PML-NBs, suggesting that the protein level of endogenous PML-I in nucleus is important for the reformation of PML-NBs that interfered by PML-RARα fusion protein. Additionally, LMB has synergistic effect with iAs III on enhancing PML-RARα fusion protein degradation, and it might provide new insight into APL treatment at clinical level in the near future.

Ret finger protein is a normal component of PML nuclear bodies and interacts directly with PML

Journal of cell science, 1998

The ret finger protein (rfp) is a member of the B-box zinc finger gene family many of which may function in growth regulation and in the appropriate context become oncogenic. Members of this family are nuclear proteins that possess a characteristic tripartite motif consisting of the RING and B-box zinc binding domains and a coiled-coil domain. The promyelocytic leukemia gene (PML), another B-box family member, produces a protein product that is detected within punctate nuclear structures called PML nuclear bodies (NBs) or PML oncogenic domains (PODs). These NBs are complex structures that consist of a number of different proteins many of which have yet to be identified. In the disease acute promyelocytic leukemia (APL) a fusion protein, PML-RARA, is produced through the t(15:17) translocation. In APL the morphology of the NBs is altered. We report that rfp co-localizes with PML in a subset of the PML NBs and that it interacts directly with PML. This interaction is mediated through t...