Perinuclear localization of slow troponin C m RNA in muscle cells is controlled by a cis-element located at its 3' untranslated region

Nuclear cardiac troponin and tropomyosin are expressed early in cardiac differentiation of rat mesenchymal stem cells

Nuclear actin - which is immunologically distinct from cytoplasmic actin - has been documented in a number of differentiated cell types, and cardiac isoforms of troponin I (cTnI) and troponin T (cTnT) have been detected in association with nuclei of adult human cardiac myocytes. It is not known whether these and related proteins are present in undifferentiated stem cells, or when they appear in cardiomyogenic cells following differentiation. We first tested the hypothesis that nuclear actin and cardiac isoforms of troponin C (cTnC) and tropomyosin (cTm) are present along with cTnI and cTnT in nuclei of isolated, neonatal rat cardiomyocytes in culture. We also tested the hypothesis that of these five proteins, only actin is present in nuclei of multipotent, bone marrow-derived mesenchymal stem cells (BM-MSCs) from adult rats in culture, but that cTnC, cTnI, cTnT and cTm appear early and uniquely following cardiomyogenic differentiation. Here we show that nuclear actin is present within nuclei of both ventricular cardiomyocytes and undifferentiated, multipotent BM-MSCs. We furthermore show that cTnC, cTnI, cTnT and cTm are not only present in myofilaments of ventricular cardiomyocytes in culture but are also within their nuclei; significantly, these four proteins appear between days 3 and 5 in both myofilaments and nuclei of BM-MSCs treated to differentiate into cardiomyogenic cells. These observations indicate that cardiac troponin and tropomyosin could have important cellular function(s) beyond Ca(2+)-regulation of contraction. While the roles of nuclear-associated actin, troponin subunits and tropomyosin in cardiomyocytes are not known, we anticipate that the BM-MSC culture system described here will be useful for elucidating their function(s), which likely involve cardiac-specific, Ca(2+)-dependent signaling in the nucleus.

Polymorphism in 3'-untranslated region of toll-like receptor 4 gene is associated with protection from hepatitis B virus recurrence after liver transplantation

BACKGROUND

Hepatitis B virus (HBV) recurrence is one of the more severe complications following liver transplantation. Toll-like receptors (TLRs) play a key role in human immunity by recognizing various bacteria, viruses, fungi, and parasites. Single nucleotide polymorphisms (SNPs) in the TLRs are thought to have an impact on the susceptibility to some pathogens. This study focused on the association between polymorphisms in the TLRs and HBV recurrence after liver transplantation in Han Chinese patients.

METHODS

A total of 41 tag SNPs in TLRs were detected by the snapshot technique in 125 patients with primary HBV-related diseases receiving liver transplantation in our center from 2004 to 2008.

RESULTS

By comparing the genetic variations and clinical data between the HBV recurrence patients and nonrecurrence patients, we found that the variant genotype of rs11536889 (TLR4) was significantly associated with HBV recurrence after liver transplantation (P = 0.040, odds ratio was 0.390, 95% confidence interval 0.159-0.957).

CONCLUSION

Our findings indicate that polymorphism in 3'-untranslated regions of the TLR4 gene may be related to protection from HBV recurrence after liver transplantation in Han Chinese patients.

Hairpin structure within the 3'UTR of DNA polymerase beta mRNA acts as a post-transcriptional regulatory element and interacts with Hax-1

Aberrant expression of DNA polymerase beta, a key enzyme involved in base excision repair, leads to genetic instability and carcinogenesis. Pol beta expression has been previously shown to be regulated at the level of transcription, but there is also evidence of post-transcriptional regulation, since rat transcripts undergo alternative polyadenylation, and the resulting 3'UTR contain at least one regulatory element. Data presented here indicate that RNA of the short 3'UTR folds to form a strong secondary structure (hairpin). Its regulatory role was established utilizing a luciferase-based reporter system. Further studies led to the identification of a protein factor, which binds to this element-the anti-apoptotic, cytoskeleton-related protein Hax-1. The results of in vitro binding analysis indicate that the formation of the RNA-protein complex is significantly impaired by disruption of the hairpin motif. We demonstrate that Hax-1 binds to Pol beta mRNA exclusively in the form of a dimer. Biochemical analysis revealed the presence of Hax-1 in mitochondria, but also in the nuclear matrix, which, along with its transcript-binding properties, suggests that Hax-1 plays a role in post-transcriptional regulation of expression of Pol beta.

Annexin A2 recognises a specific region in the 3'-UTR of its cognate messenger RNA

Annexin A2 is a multifunctional Ca(2+)- and lipid-binding protein. We previously showed that a distinct pool of cellular Annexin A2 associates with mRNP complexes or polysomes associated with the cytoskeleton. Here we report in vitro and in vivo experiments showing that Annexin A2 present in this subset of mRNP complexes interacts with its cognate mRNA and c-myc mRNA, but not with beta(2)-microglobulin mRNA translated on membrane-bound polysomes. The protein recognises sequence elements within the untranslated regions, but not within the coding region, of its cognate mRNA. Alignment of the Annexin A2-binding 3'-untranslated regions of annexin A2 mRNA from several species reveals a five nucleotide consensus sequence 5'-AA(C/G)(A/U)G. The Annexin A2-interacting region of the 3'-untranslated region can be mapped to a sequence of about 100 nucleotides containing two repeats of the consensus sequence. The binding elements appear to involve both single and double stranded regions, indicating that a specific higher order mRNA structure is required for binding to Annexin A2. We suggest that this type of interaction is representative for a group of mRNAs translated on cytoskeleton-bound polysomes.

A systematic analysis of disease-associated variants in the 3' regulatory regions of human protein-coding genes II: the importance of mRNA secondary structure in assessing the functionality of 3' UTR variants

In an attempt both to catalogue 3' regulatory region (3' RR)-mediated disease and to improve our understanding of the structure and function of the 3' RR, we have performed a systematic analysis of disease-associated variants in the 3' RRs of human protein-coding genes. We have previously analysed the variants that have occurred in two specific domains/motifs of the 3' untranslated region (3' UTR) as well as in the 3' flanking region. Here we have focused upon 83 known variants within the upstream sequence (USS; between the translational termination codon and the upstream core polyadenylation signal sequence) of the 3' UTR. To place these variants in their proper context, we first performed a comprehensive survey of known cis-regulatory elements within the USS and the mechanisms by which they effect post-transcriptional gene regulation. Although this survey supports the view that RNA regulatory elements function within the context of specific secondary structures, there are no general rules governing how secondary structure might exert its influence. We have therefore addressed this question by systematically evaluating both functional and non-functional (based upon in vitro reporter gene and/or electrophoretic mobility shift assay data) USS variant-containing sequences against known cis-regulatory motifs within the context of predicted RNA secondary structures. This has allowed us not only to establish a reliable and objective means to perform secondary structure prediction but also to identify consistent patterns of secondary structural change that could potentiate the discrimination of functional USS variants from their non-functional counterparts. The resulting rules were then used to infer potential functionality in the case of some of the remaining functionally uncharacterized USS variants, from their predicted secondary structures. This not only led us to identify further patterns of secondary structural change but also several potential novel cis-regulatory motifs within the 3' UTRs studied.