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Altered expression of heterogenous nuclear ribonucleoproteins and SR factors in human colon adenocarcinomas
1Istituto di Genetica Biochimica ed Evoluzionistica Consiglio Nazionale delle Ricerche, Università di Pavia, Istituto di Ricovero e Cura a Carattere Scientifico Policlinico San Matteo, Italy.
Abstract:
Alternative splicing is part of the expression program of a wide number of genes implicated in cell growth and differentiation. Although the occurrence of inappropriate alternative splicing in tumors has started to emerge, the underlying molecular mechanisms have been, thus far, largely unexplored. We have investigated the alternative splicing pattern of the CD44 gene in specimens of nonfamilial colon adenocarcinomas at different stages of tumor progression. In the same patients, we have assessed by Northern blotting analysis the mRNA levels of different heterogeneous nuclear ribonucleoproteins and SR factors, all involved in pre-mRNA splicing and, more in general, in mRNA maturation. The results of this analysis highlight a general rule for the mode of splicing of the CD44 pre-mRNA. Moreover, we found that the mRNA levels of different SR proteins in tumor specimens are different from, and usually lower than, those detected in samples of nonpathological tissue adjacent to the tumor. Quantitative analysis demonstrates that, in tumors, the mRNA levels of ASF, SRp40, SRp55, and SRp75, when normalized to those of heterogeneous nuclear ribonucleoprotein A1, are lower than those of SRp20 and SRp30. Interestingly, this reduction is more drastic in patients showing a more altered CD44 splicing pattern and seems to be related to the propensity to develop metastases.
Insights
Altered CD44 gene splicing in colon tumors correlates with lower levels of specific SR proteins. This splicing dysregulation is more pronounced in advanced cancers and linked to metastasis risk.
Area of Science:
- Molecular Biology
- Cancer Research
- Genetics
Background:
- Alternative splicing regulates gene expression in cell growth and differentiation.
- Aberrant alternative splicing is observed in tumors, but mechanisms are poorly understood.
- The CD44 gene is crucial in cell adhesion and is frequently altered in cancer.
Purpose of the Study:
- To investigate the alternative splicing patterns of the CD44 gene in colon adenocarcinomas.
- To analyze the mRNA levels of splicing factors (hnRNPs and SR proteins) in tumor tissues.
- To correlate splicing alterations with tumor progression and metastatic potential.
Main Methods:
- Analysis of CD44 pre-mRNA splicing in colon adenocarcinoma specimens.
- Northern blotting to quantify mRNA levels of heterogeneous nuclear ribonucleoproteins (hnRNPs) and SR factors.
- Quantitative analysis of specific SR protein mRNA levels relative to hnRNP A1.
Main Results:
- A specific splicing pattern for CD44 pre-mRNA was identified in colon tumors.
- mRNA levels of several SR proteins (ASF, SRp40, SRp55, SRp75) were significantly lower in tumor tissues compared to adjacent non-pathological tissues.
- Reduced SR protein levels, particularly ASF, SRp40, SRp55, and SRp75 relative to hnRNP A1, were more pronounced in advanced tumors and correlated with CD44 splicing alterations.
- The degree of CD44 splicing alteration and reduced SR protein levels correlated with the propensity for metastasis.
Conclusions:
- Dysregulation of alternative splicing, specifically in the CD44 gene, is a feature of colon tumorigenesis.
- Reduced expression of key SR proteins contributes to aberrant CD44 splicing in colon cancer.
- Splicing factor alterations and CD44 splicing patterns may serve as biomarkers for tumor progression and metastasis risk.