Antisense inhibition of membrane-bound human interleukin-5 receptor-alpha chain does not affect soluble receptor expression and induces apoptosis in TF-1 cells

Steering research on mRNA splicing in cancer towards clinical translation

Splicing factors are affected by recurrent somatic mutations and copy number variations in several types of haematologic and solid malignancies, which is often seen as prima facie evidence that splicing aberrations can drive cancer initiation and progression. However, numerous spliceosome components also 'moonlight' in DNA repair and other cellular processes, making their precise role in cancer difficult to pinpoint. Still, few would deny that dysregulated mRNA splicing is a pervasive feature of most cancers. Correctly interpreting these molecular fingerprints can reveal novel tumour vulnerabilities and untapped therapeutic opportunities. Yet multiple technological challenges, lingering misconceptions, and outstanding questions hinder clinical translation. To start with, the general landscape of splicing aberrations in cancer is not well defined, due to limitations of short-read RNA sequencing not adept at resolving complete mRNA isoforms, as well as the shallow read depth inherent in long-read RNA-sequencing, especially at single-cell level. Although individual cancer-associated isoforms are known to contribute to cancer progression, widespread splicing alterations could be an equally important and, perhaps, more readily actionable feature of human cancers. This is to say that in addition to 'repairing' mis-spliced transcripts, possible therapeutic avenues include exacerbating splicing aberration with small-molecule spliceosome inhibitors, targeting recurrent splicing aberrations with synthetic lethal approaches, and training the immune system to recognize splicing-derived neoantigens.

RNA splicing dysregulation and the hallmarks of cancer

Dysregulated RNA splicing is a molecular feature that characterizes almost all tumour types. Cancer-associated splicing alterations arise from both recurrent mutations and altered expression of trans-acting factors governing splicing catalysis and regulation. Cancer-associated splicing dysregulation can promote tumorigenesis via diverse mechanisms, contributing to increased cell proliferation, decreased apoptosis, enhanced migration and metastatic potential, resistance to chemotherapy and evasion of immune surveillance. Recent studies have identified specific cancer-associated isoforms that play critical roles in cancer cell transformation and growth and demonstrated the therapeutic benefits of correcting or otherwise antagonizing such cancer-associated mRNA isoforms. Clinical-grade small molecules that modulate or inhibit RNA splicing have similarly been developed as promising anticancer therapeutics. Here, we review splicing alterations characteristic of cancer cell transcriptomes, dysregulated splicing's contributions to tumour initiation and progression, and existing and emerging approaches for targeting splicing for cancer therapy. Finally, we discuss the outstanding questions and challenges that must be addressed to translate these findings into the clinic.

Interleukin-5 does not influence differential transcription of transmembrane and soluble isoforms of IL-5R alpha in vivo

Interleukin-5 (IL-5) promotes signal transduction and expansion of eosinophil colonies in bone marrow via interactions with its heterodimeric receptor (IL-5R). Two variants encoding soluble forms of the alpha subunit (sIL-5R alpha) have been described, although the signals promoting and/or limiting differential transcription remain to be clarified.

OBJECTIVES

Our intent was to explore the role of IL-5 in regulating differential transcription of these splice variants in vivo.

METHODS

We have designed a quantitative reverse transcriptase-polymerase chain reaction assay to detect transcripts encoding the transmembrane, soluble 1 and 2 forms of IL-5R alpha in two strains of wild-type (BALB/c and C57BL/6) and corresponding IL-5 gene-deleted mice. Wild-type mice respond to S. mansoni infection with a gradual increase in serum IL-5 and eosinophilia, which is not observed in IL-5 gene-deleted mice.

RESULTS AND CONCLUSIONS

We find that IL-5 is not necessary for differential splicing to occur in vivo, as all three forms of the IL-5R alpha are detected in both strains of IL-5 gene-deleted mice, with ratios of transcript expression (transmembrane : soluble 1 : soluble 2) that were indistinguishable from their wild-type counterparts. Differential splicing does vary markedly between strains, potentially because of local effects of strain-specific polymorphisms.

The concept and application of antisense oligonucleotides

Since the identification of the double-stranded DNA helix by Watson and Crick in 1953, the knowledge of nucleotide structure and function has been an important potential tool in the study and therapy of disease. There is recent clinical evidence that antisense oligonucleotides may be important therapeutic compounds in the clinical therapy of a range of diseases, including infection (viruses and bacteria), oncology, and inflammation. Our laboratory-based understanding of antisense oligonucleotide activity has provided a foundation for their use in several human diseases. Potentially relevant applications include inflammatory bowel disease therapy, psoriasis, transplantation, rheumatoid arthritis, cytomegalovirus retinitis, hepatitis C, and solid tumor therapy. Here we will outline these applications as well as our ongoing clinical trials for Crohn's disease.