Intracellular trafficking of hnRNP A2 in oligodendrocytes.

Heterogeneous ribonucleoprotein (hnRNP) A2 is a trans-acting factor that mediates intracellular trafficking of specific RNAs containing the A2 response element. HnRNP A2 is localized in the nucleus and also in granules in the perikaryon and processes in oligodendrocytes. The distribution of the cytoplasmic pool of hnRNP A2 is microtubule-dependent. HnRNP A2 is composed of two sequential RNA binding domains (RBDI and RBDII), a glycine-rich domain, and a nuclear import domain (M9). In order to analyze the roles of individual domains in determining the intracellular distribution of hnRNP A2, chimeric mRNAs encoding various domains fused with green fluorescent protein (GFP) were injected into oligodendrocytes, and the subcellular distribution of the GFP hybrid proteins was analyzed by fluorescence microscopy. Chimeric GFP proteins containing the M9 domain were localized to the nucleus. In the absence of the M9 domain, proteins containing the RBDII domain were preferentially concentrated in the distal processes of the cells. Localization of RBDII-containing proteins in the periphery was dependent on the presence of intact microtubules. These data suggest that the RBDII domain of hnRNP A2 targets hnRNP A2 to the periphery of the cell in a microtubule-dependent manner.