C-terminal domain of MEIS1 converts PKNOX1 (PREP1) into a HOXA9-collaborating oncoprotein

Abstract

The three-amino-acid loop extension (TALE) class homeodomain proteins MEIS1 and PKNOX1 (PREP1) share the ability to interact with PBX and HOX family members and bind similar DNA sequences but appear to play opposing roles in tumor development. Elevated levels of MEIS1 accelerate development of HOX-and MLL-induced leukemias, and this pro-tumorigenic property has been associated with transcriptional activity of MEIS1. In contrast, reduction of PKNOX1 levels has been linked with cancer development despite the absence of an identifiable transactivating domain. In this report, we show that a chimeric protein generated by fusion of the MEIS1 C-terminal region encompassing the transactivating domain with the full-length PKNOX1 (PKNOX1- MC IntroductionThere is a compelling body of evidence implicating the HOX transcription factors and their cofactors PBX and MEIS/PKNOX-(PREP) in leukemogenesis (reviewed by Argiropoulos et al 1 ). In particular, deregulated expression of HOXA9 has been detected in a large proportion of human acute myeloid (AML) and lymphoid leukemias (ALLs) [2][3][4][5] and is associated with poor prognosis for refractory AML. 2 A significant proportion of these leukemias, especially those harboring MLL rearrangements, also overexpress MEIS1, [3][4][5][6] indicating that activation of MEIS1 may represent a key collaborating genetic event in leukemia development.MEIS1 is a member of the TALE class of homeoproteins, which includes the PBX and MEIS/PKNOX protein families characterized by an atypical homeodomain (HD) containing a three-amino acid loop extension (TALE) between the first 2 ␣-helices. 7 MEIS1/PKNOX1 and PBX1 proteins physically interact with each other using the bipartite Homothorax-MEIS domain (HM A /HM B ) and the PBC-A domain of PBX. 8,9 This interaction was reported to enhance the stability of the heterodimers and to promote their nuclear localization. [10][11][12] MEIS1 and PBX1 also form heterodimers with HOX proteins in a DNAdependent manner and have been reported to form triple complexes composed of MEIS1/PKNOX1, PBX1, and HOX in both a DNA-independent 13,14 and DNA-dependent manner, 15 suggesting that, in some cellular contexts, a triple HOX-PBX-MEIS/PKNOX complex is required for HOX-mediated gene regulation. 15,16 The combinatorial diversity generated by 39 different Hox, 3 Meis, 2 Pknox, and 4 Pbx gene products probably enables formation of distinct regulatory complexes targeting numerous genomic loci in a cell context-dependent manner.Using a bone marrow transduction/transplantation-based experimental model, we showed that overexpression of Meis1 significantly accelerates the onset of Hoxa9-induced AML, 17,18 and similar collaborative Meis1 effects were reported for other Hox and Hox-fusion genes tested. 19,20 High levels of Meis1 expression also appeared to be the rate-limiting factor for development of Mllinduced leukemias, 21 implying that Meis1 activity is necessary to create and/or maintain cellular context required for tumor development. Pknox1 overexpression, in contrast, fai...

The miR-17∼92 cluster contributes to MLL leukemia through the repression of MEIS1 competitor PKNOX1

“…PKNOX1 and MEIS1 are highly homologous in the domains required for both PBX interaction and DNA binding and interact with the same surface on PBX partners [31]. However, the oncogenic activity of MEIS1 is located in the C-terminal domain, which differs from that of PKNOX1 [27, 32, 33]. Meis1 cooperates with Hoxa9 in leukemic transformation; whereas co-expression of Pknox1 with Hoxa9 lacks this effect [32].…”

“…However, the oncogenic activity of MEIS1 is located in the C-terminal domain, which differs from that of PKNOX1 [27, 32, 33]. Meis1 cooperates with Hoxa9 in leukemic transformation; whereas co-expression of Pknox1 with Hoxa9 lacks this effect [32]. However, chimeric Pknox1 proteins which append the Meis1 C-terminus to the Pknox1 protein can restore acceleration of leukemia development [32].…”

“…MIGR1 [37], MSCV-MLL-AF9 [37], and MSCV-pKOF2-Prep1-EGFP [32] retroviral constructs were previously described. Bone marrow isolation, enrichment, and infection for generation of MLL-AF9 transformed bone marrow was performed as previously described [7].…”

Prep1 and Meis1 competition for Pbx1 binding regulates protein stability and tumorigenesis

“…Second, the Meis1 CTD is required for HoxA9 cooperation in leukemogenesis (18,34,35). However, swapping the Prep1 with the Meis1 CTD has failed to convert Prep1 into an HoxA9-cooperating oncogene (36), which succeeds, however, when a full-length Prep1 is lengthened with the Meis1-CTD that induces Meis1-specific gene sets (36). However, these data do not prove that the central mechanism is transcriptional, because no studies of protein levels were carried out and there is peculiarity of the Prep1-Meis1 chimeric protein carrying both CTDs.…”

Biochemistry of the tale transcription factors PREP, MEIS, and PBX in vertebrates

“…Indeed, addition of the carboxyterminal domain of MEIS1 to the full-length PREP1 protein transforms it from a tumor suppressor into an oncogene; intriguingly, the same result is not obtained by substitution of the PREP1 C-terminus with that of Meis1 (Bisaillon et al, 2011). …”