Nuclear actin is associated with a specific subset of hnRNP A/B-type proteins

Abstract

Pre-mRNP complexes were isolated from rat liver nuclei as 40S hnRNP particles, and actin-binding proteins were collected by DNase I affinity chromatography. The bound proteins were analyzed by 2D gel electrophoresis, and the following five hnRNP A/B-type proteins were identified by tandem mass spectrometry: DBP40/CBF-A (CArG binding factor A), a minor hnRNP A2 variant and three minor hnRNP A3 (mBx) variants. DBP40 was chosen for further analysis of the association of actin with the pre-mRNP complex. It was shown in vitro that purified actin binds to recombinant DBP40 suggesting that the interaction between actin and DBP40 is direct in the pre-mRNP particles. The association of actin with DBP40 was further explored in vivo. It was shown in a transfection study that DBP40 appears both in the nucleus and cytoplasm. Microinjection experiments revealed that DBP40 is exported from the nucleus to the cytoplasm. Finally, RNA-protein and protein-protein cross-linking experiments showed that DBP40 interacts with poly(A)(+) RNA as well as actin, both in the nucleus and cytoplasm. We propose that actin associated with DBP40, and perhaps with additional hnRNP A/B-type proteins, is transferred from nucleus to cytoplasm bound to mRNA.

Scaffold/Matrix Attachment Regions (S/MARs): Relevance for Disease and Therapy

“…Although a direct participation in the nuclear matrix has remained uncertain, there have been hints for their interaction with nuclear RNAs and with proteins from hnRNP complexes (Percipalle et al 2002), which, according to Kukalev et al (2005), are essential for productive pol II transcription. Other studies demonstrate that antibodies against β-actin inhibit pol II transcription in a mammalian system for which actin was detected as a component of pre-initiation complexes and where it played a role in initiation (Hofmann et al 2004).…”

Active maintenance of nuclear actin by importin 9 supports transcription

“…Actin is a component of many chromatin remodelling complexes (2,3), associates with all three RNA polymerases (4)(5)(6), and also binds to factors regulating pre-mRNA processing and export (7)(8)(9). In addition to these general roles in gene expression, actin has also been linked to regulation of specific sets of genes.…”

Invasive breast cancer cells exhibit increased mobility of the actin‐binding protein CapG

“…A transactivation activity of the CapG protein was called into question, but a modulation of transcriptional activators was discussed. 3 Several studies have provided evidence that nuclear actin associates with three types of nuclear complexes involved in gene expression: chromatin remodeling complexes, [10][11][12] ribonucleoprotein particles 13,14 and the three RNA polymerases. [15][16][17] CapG as a nuclear actin-binding protein could play a role in preventing the nuclear actin from polymerizing and keeping it in a monomeric globular or a short oligomeric form.…”