The hnRNPs F and H2 bind to similar sequences to influence gene expression

Abstract

The hnRNPs (heterogeneous nuclear ribonucleoproteins) F and H2 share a similar protein structure. Both have been implicated as regulating polyadenylation, but hnRNP H2 had a positive effect, whereas hnRNP F acted negatively. We therefore carried out side-by-side comparisons of their RNA-binding and in vivo actions. The binding of the CstF2 (64 kDa cleavage stimulatory factor) to SV40 (simian virus 40) late pre-mRNA substrates containing a downstream GRS (guanine-rich sequence) was reduced by hnRNP F, but not by hnRNP H2, in a UV-cross-linking assay. Point mutations of the 14-nt GRS influenced the binding of purified hnRNP F or H2 in parallel. Co-operative binding of the individual proteins to RNA was lost with mutations of the GRS in the G1-5 or G12-14 regions; both regions seem to be necessary for optimal interactions. Using a reporter green fluorescent protein assay with the GRS inserted downstream of the poly(A) (polyadenine) signal, expression in vivo was diminished by a mutant G1-5 sequence which decreased binding of both hnRNPs (SAA20) and was enhanced by a 12-14-nt mutant that showed enhanced hnRNP F or H2 binding (SAA10). Using small interfering RNA, down-regulation of hnRNP H2 levels diminished reporter expression, confirming that hnRNP H2 confers a positive influence; in contrast, decreasing hnRNP F levels had a negligible influence on reporter expression with the intact GRS. A pronounced diminution in reporter expression was seen with the SAA20 mutant for both. Thus the relative levels of hnRNP F and H2 in cells, as well as the target sequences in the downstream GRS on pre-mRNA, influence gene expression.

Regulation of global and specific mRNA translation by the mTOR signaling pathway

“…93 Our results indicate that mTOR stimulates the recruitment of some hnRNP isoforms to the 5' mRNA cap, 72 which may provide a regulated mechanism for the selective recruitment of mRNAs to the translational machinery. Consistent with this possibility, is the fact that hnRNP A1 and F have been shown to regulate the translation of specific mRNAs 95,96 ; however, the involvement of mTOR in this process is currently unknown.…”

Dysregulation of miR-212 Promotes Castration Resistance through hnRNPH1-Mediated Regulation of AR and AR-V7: Implications for Racial Disparity of Prostate Cancer

“…These proteins possess a modular and highly conserved structure encompassing two glycine-rich auxiliary domains and two or three repeats of RNA binding quasi-RNA recognition motif (qRRM). The hnRNP H/F members regulate both inhibitory and stimulatory alternative splicing of target genes through binding cognate Grich intronic and exonic sequences in proximity to the polyadenylation sites (13).…”

Hide and Go Seek: Activation of the Secretory-Specific Poly (A) Site of Igh by Transcription Elongation Factors

“…While hnRNP F might be expected to block any poly(A) site based on its sequence preference for downstream regions (Alkan, Martincic et al 2006), we found by a micro-array analyses of hnRNP F transfected cells that only some genes were affected, most notable among these were secretory Igh and ELL2, a transcription elongation factor (Martincic, Alkan et al 2009). The finding that there are U1A binding sites up-stream of the Igh mu secretory poly(A) site indicates a selectivity consistent with the observed increased use of the site when U1A levels fall (Phillips and Virtanen 1997).…”

“…A shift in the SR-proteins is seen from the activating type (ASF/SF2) in B-cells to the repression type (SRp20) in plasma cells. The factors hnRNP F and U1A, both of which block the secretory-specific poly(A) site from functioning, are reduced in plasma cells (Veraldi, Arhin et al 2001;Milcarek, Martincic et al 2003;Alkan, Martincic et al 2006) and (Ma, Gunderson et al 2006) which would allow the secretory site to function better. The major effectors in the alternative processing in B versus plasma cells are summarized in Table 1.…”