Differentiation-Dependent Cytoplasmic Distribution and in Vivo RNA Association of Proteins Recognized by the 3′-UTR Stability Element of α-Globin mRNA in Erythroleukemic Cells

In this study, we analyzed subcytoplasmic distribution and in vivo RNA association of proteins with specific affinity to cytosine-rich stability determinant sequences of α-globin mRNA 3′-UTR in a MEL-707 erythroleukemic model. We took advantage of the possibility that these cells can be reversibly differentiated (as a continuous population, but not at the level of individual cells) which, therefore, allows analysis of various stages of erythroid differentiation within the same cell population. Label transfer experiments revealed four major complexes with molecular mass of 110-, 70-, 55- and 50-kDa in various cytoplasmic fractions. Using the combination of in vitro label transfer and in vivo UV-crosslinking techniques, we also demonstrated that subcytoplasmic distribution as well as in vivo RNA association of various complex-forming proteins is differentiation dependent in MEL-707 cells. These results indicate that changes in the cytoplasmic environment imposed by the differentiating stimulus might direct important biochemical signals as to how the stability determinant 3′UTR elements interact with their binding proteins. These data also suggest that stability complexes are dynamic macromolecular structures with high response capacity to various extra- and intracellular regulatory stimuli.