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CDNA cloning reveals two mouse beta5 integrin transcripts distinct in cytoplasmic domains as a result of alternative splicing.

ABSTRACT: The integrin beta5 subunit has only been found to form a heterodimer with subunit alphav which acts as a vitronectin receptor. Integrin alphavbeta5 has been implicated in cell migration and growth factor-induced angiogenesis. In the present study, a mouse liver cDNA library was screened using a human beta5 cDNA fragment obtained by reverse transcriptase PCR (RT-PCR). Three of the clones (MB5, MB15 and MB17) overlapped to give an open reading frame, called beta5A, which is homologous to the human beta5 subunit. The sequence of another clone (MB26), called beta5B, was identical with beta5A, except for a deletion of 29 bp near the 3' end of the open reading frame. The 29 bp deletion resulted in an open-reading-frame shift and a completely different C-terminal sequence in beta5B. beta5A and beta5B were shown, by RT-PCR, to be co-expressed in most mouse tissues tested, although beta5B mRNA was detected at much lower levels than beta5A. beta5A and beta5B mRNAs were also detected in the mouse monocytic cell line, J774, and in isolated mouse peritoneal macrophages. Adhesion of peritoneal macrophages has been shown to up-regulate the expression of both beta5A and beta5B mRNAs. The 29 bp sequence begins with a putative intron-splicing donor site (GTGAT...). A 3' fragment of the mouse integrin beta5 gene was cloned by PCR and sequenced showing that the 29 bp sequence was also immediately followed by an intron. Therefore, the 29 bp sequence was apparently expressed as part of the beta5A mRNA but was spliced out as part of the downstream intron in beta5B. Since the cytoplasmic domains of the integrin beta subunits are important in cytoskeleton attachment and signalling, the two alternatively spliced beta5 isoforms may have distinct roles in cell adhesion and other cellular functions.

SUBMITTER: Zhang H

PROVIDER: S-EPMC1219398 | biostudies-other | 1998 Apr

REPOSITORIES: biostudies-other

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Project description:BACKGROUND: Alternative splicing (AS) is a central mechanism in the generation of genomic complexity and is a major contributor to transcriptome and proteome diversity. Alterations of the splicing process can lead to deregulation of crucial cellular processes and have been associated with a large spectrum of human diseases. Cancer-associated transcripts are potential molecular markers and may contribute to the development of more accurate diagnostic and prognostic methods and also serve as therapeutic targets. Alternative splicing-enriched cDNA libraries have been used to explore the variability generated by alternative splicing. In this study, by combining the use of trapping heteroduplexes and RNA amplification, we developed a powerful approach that enables transcriptome-wide exploration of the AS repertoire for identifying AS variants associated with breast tumor cells modulated by ERBB2 (HER-2/neu) oncogene expression. RESULTS: The human breast cell line (C5.2) and a pool of 5 ERBB2 over-expressing breast tumor samples were used independently for the construction of two AS-enriched libraries. In total, 2,048 partial cDNA sequences were obtained, revealing 214 alternative splicing sequence-enriched tags (ASSETs). A subset with 79 multiple exon ASSETs was compared to public databases and reported 138 different AS events. A high success rate of RT-PCR validation (94.5%) was obtained, and 2 novel AS events were identified. The influence of ERBB2-mediated expression on AS regulation was evaluated by capillary electrophoresis and probe-ligation approaches in two mammary cell lines (Hb4a and C5.2) expressing different levels of ERBB2. The relative expression balance between AS variants from 3 genes was differentially modulated by ERBB2 in this model system. CONCLUSIONS: In this study, we presented a method for exploring AS from any RNA source in a transcriptome-wide format, which can be directly easily adapted to next generation sequencers. We identified AS transcripts that were differently modulated by ERBB2-mediated expression and that can be tested as molecular markers for breast cancer. Such a methodology will be useful for completely deciphering the cancer cell transcriptome diversity resulting from AS and for finding more precise molecular markers.

Project description:The killer-cell Ig-like receptors (KIR) form a multigene entity involved in modulating immune responses through interactions with MHC class I molecules. The complexity of the KIR cluster is reflected by, for instance, abundant levels of allelic polymorphism, gene copy number variation, and stochastic expression profiles. The current transcriptome study involving human and macaque families demonstrates that KIR family members are also subjected to differential levels of alternative splicing, and this seems to be gene dependent. Alternative splicing may result in the partial or complete skipping of exons, or the partial inclusion of introns, as documented at the transcription level. This post-transcriptional process can generate multiple isoforms from a single KIR gene, which diversifies the characteristics of the encoded proteins. For example, alternative splicing could modify ligand interactions, cellular localization, signaling properties, and the number of extracellular domains of the receptor. In humans, we observed abundant splicing for KIR2DL4, and to a lesser extent in the lineage III KIR genes. All experimentally documented splice events are substantiated by in silico splicing strength predictions. To a similar extent, alternative splicing is observed in rhesus macaques, a species that shares a close evolutionary relationship with humans. Splicing profiles of Mamu-KIR1D and Mamu-KIR2DL04 displayed a great diversity, whereas Mamu-KIR3DL20 (lineage V) is consistently spliced to generate a homolog of human KIR2DL5 (lineage I). The latter case represents an example of convergent evolution. Although just a single KIR splice event is shared between humans and macaques, the splicing mechanisms are similar, and the predicted consequences are comparable. In conclusion, alternative splicing adds an additional layer of complexity to the KIR gene system in primates, and results in a wide structural and functional variety of KIR receptors and its isoforms, which may play a role in health and disease.

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CDNA cloning reveals two mouse beta5 integrin transcripts distinct in cytoplasmic domains as a result of alternative splicing.

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