ABSTRACT
Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) is a chimeric protein expressed in a subset of cases of anaplastic large cell lymphoma (ALCL) for which constitutive expression represents a key oncogenic event. The ALK signaling pathway is complex and probably involves functional redundancy between various signaling substrates of ALK. Despite numerous studies on signaling mediators, the molecular mechanisms contributing to the distinct oncogenic features of NPM-ALK remain incompletely understood. The search for additional interacting partners of NPM-ALK led to the discovery of AUF1/hnRNPD, a protein implicated in AU-rich element (ARE)-directed mRNA decay. AUF1 was immunoprecipitated with ALK both in ALCL-derived cells and in NIH3T3 cells stably expressing NPM-ALK or other X-ALK fusion proteins. AUF1 and NPM-ALK were found concentrated in the same cytoplasmic foci, whose formation required NPM-ALK tyrosine kinase activity. AUF1 was phosphorylated by ALK in vitro and was hyperphosphorylated in NPM-ALK-expressing cells. Its hyperphosphorylation was correlated with increased stability of several AUF1 target mRNAs encoding key regulators of cell proliferation and with increased cell survival after transcriptional arrest. Thus, AUF1 could function in a novel pathway mediating the oncogenic effects of NPM-ALK. Our data establish an important link between oncogenic kinases and mRNA turnover, which could constitute a critical aspect of tumorigenesis.
Subject(s)
Heterogeneous-Nuclear Ribonucleoprotein D/metabolism , Lymphoma, Large B-Cell, Diffuse/metabolism , Oncogene Proteins, Fusion/metabolism , Protein-Tyrosine Kinases/metabolism , Amino Acid Sequence , Animals , Cell Death , Cyclins/genetics , Genes, myc , Heterogeneous Nuclear Ribonucleoprotein D0 , Humans , Lymphoma, Large B-Cell, Diffuse/etiology , Lymphoma, Large B-Cell, Diffuse/genetics , Mice , Models, Biological , Molecular Sequence Data , NIH 3T3 Cells , Oncogene Proteins, Fusion/genetics , Phosphorylation , Protein-Tyrosine Kinases/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Neoplasm/genetics , RNA, Neoplasm/metabolism , TransfectionABSTRACT
The molecular basis for the initial specification of dorsoventral polarity in the Amphibian egg prior to the mid-blastula transition still remains an open question. Regional differences in the protein pattern of Pleurodeles egg were investigated during early cleavage (8- and 512-cell stages, prior to the mid-blastula transition). Animal-dorsal, animal-ventral, vegetal-dorsal and vegetal-ventral quarters were separated and proteins were analyzed by 2D-electrophoresis. The comparison of acidic protein patterns from dorsal and ventral quarters revealed differences between vegetal cells but no difference was detected between animal cells. One protein (p11, 30 kDa) was characterized in the dorsal side as early as the 8-cell st. and two dorsal spots were detected at the 512-cell st. (p11 and p5, 65 kDa). Similarly one protein (p7b, 46 kDa) appears to be ventral-specific from the 8-cell st. The p11 spot was shown to appear in ventral cells as a consequence of a dorsalizing LiCl-treatment at the 32-cell stage. Conversely, p11 disappeared from dorsal cells and p5 did not appear at 512-cell stage after UV-irradiation of the uncleaved egg, which results in the expression of the ventral-specific protein p7b in the dorsal part of the egg. Therefore differential protein expression is already present at very early cleavage stages. Its significance needs further investigation.
