Biomedical subjects

Robert A Hasman

Publications and source records attributed to Robert A Hasman.

3 recordsLinked to original sources

PubMed2006

Hu proteins regulate polyadenylation by blocking sites containing U-rich sequences.

A recent genome-wide bioinformatic analysis indicated that 54% of human genes undergo alternative polyadenylation. Although it is clear that differential selection of poly(A) sites can alter gene expression, resulting in significant biological consequences, the mechanisms that regulate polyadenylation are poorly understood. Here we report that the neuron-specific members of a family of RNA-binding proteins, Hu proteins, known to regulate mRNA stability and translation in the cytoplasm, play an important role in polyadenylation regulation. Hu proteins are homologs of the Drosophila embryonic lethal abnormal visual protein and contain three RNA recognition motifs. Using an in vitro polyadenylation assay with HeLa cell nuclear extract and recombinant Hu proteins, we have shown that Hu proteins selectively block both cleavage and poly(A) addition at sites containing U-rich sequences. Hu proteins have no effect on poly(A) sites that do not contain U-rich sequences or sites in which the U-rich sequences are mutated. All three RNA recognition motifs of Hu proteins are required for this activity. Overexpression of HuR in HeLa cells also blocks polyadenylation at a poly(A) signal that contains U-rich sequences. Hu proteins block the interaction between the polyadenylation cleavage stimulation factor 64-kDa subunit and RNA most likely through direct interaction with poly(A) cleavage stimulation factor 64-kDa subunit and cleavage and polyadenylation specificity factor 160-kDa subunit. These studies identify a novel group of mammalian polyadenylation regulators. Furthermore, they define a previously unknown nuclear function of Hu proteins.

Animals↗

PubMed2006

A nuclear function of Hu proteins as neuron-specific alternative RNA processing regulators.

Recent advances in genome-wide analysis of alternative splicing indicate that extensive alternative RNA processing is associated with many proteins that play important roles in the nervous system. Although differential splicing and polyadenylation make significant contributions to the complexity of the nervous system, our understanding of the regulatory mechanisms underlying the neuron-specific pathways is very limited. Mammalian neuron-specific embryonic lethal abnormal visual-like Hu proteins (HuB, HuC, and HuD) are a family of RNA-binding proteins implicated in neuronal differentiation and maintenance. It has been established that Hu proteins increase expression of proteins associated with neuronal function by up-regulating mRNA stability and/or translation in the cytoplasm. We report here a novel function of these proteins as RNA processing regulators in the nucleus. We further elucidate the underlying mechanism of this regulation. We show that in neuron-like cells, Hu proteins block the activity of TIA-1/TIAR, two previously identified, ubiquitously expressed proteins that promote the nonneuronal pathway of calcitonin/calcitonin gene-related peptide (CGRP) pre-mRNA processing. These studies define not only the first neuron-specific regulator of the calcitonin/CGRP system but also the first nuclear function of Hu proteins.

Alternative Splicing↗

PubMed2003

U1 snRNP-dependent function of TIAR in the regulation of alternative RNA processing of the human calcitonin/CGRP pre-mRNA.

Alternative RNA processing of human calcitonin/CGRP pre-mRNA is regulated by an intronic enhancer element. Previous studies have demonstrated that multiple sequence motifs within the enhancer and a number of trans-acting factors play critical roles in the regulation. Here, we report the identification of TIAR as a novel player in the regulation of human calcitonin/CGRP alternative RNA processing. TIAR binds to the U tract sequence motif downstream of a pseudo 5' splice site within the previously characterized intron enhancer element. Binding of TIAR promotes inclusion of the alternative 3'-terminal exon located more than 200 nucleotides upstream from the U tract. In cells that preferentially include this exon, overexpression of a mutant TIAR that lacks the RNA binding domains suppressed inclusion of this exon. In this report, we also demonstrate an unusual novel interaction between U6 snRNA and the pseudo 5' splice site, which was shown previously to bind U1 snRNA. Interestingly, TIAR binding to the U tract sequence depends on the interaction of not only U1 but also U6 snRNA with the pseudo 5' splice site. Conversely, TIAR binding promotes U6 snRNA binding to its target. The synergistic relationship between TIAR and U6 snRNA strongly suggests a novel role of U6 snRNP in regulated alternative RNA processing.

Alternative Splicing↗