SRSF1 shapes 3'-end site selection with differential dependence on U1 snRNP

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Regulation

Background:

• Proper polyadenylation site (PAS) selection is crucial for determining RNA isoforms.
• Core spliceosomal components like U1 snRNP are known to regulate PAS choice.
• The role of other splicing factors, such as SRSF1, in conjunction with U1 snRNP in PAS selection remained unclear.

Purpose of the Study:

• To investigate the role of splicing factor SRSF1 in polyadenylation site (PAS) selection.
• To elucidate the mechanisms by which SRSF1 regulates PAS choice, including its independence from and interaction with U1 snRNP.
• To determine how SRSF1 influences RNA isoform determination and gene expression.

Main Methods:

• RNA binding assays to detect SRSF1 interaction with RNA near proximal PASs.
• Analysis of 3' UTR sequences and PAS usage in breast cancer tumors with altered SRSF1 levels.
• Investigating SRSF1-U1 snRNP-Pol II interactions.
• Measuring Pol II elongation index and transcription readthrough.

Main Results:

• SRSF1 directly binds RNA near proximal PASs in 3' UTRs, promoting their usage independently of U1 snRNP.
• Altered SRSF1 levels in breast cancer tumors correlate with shifted 3'-end selection.
• SRSF1 interacts with U1 snRNP to modulate SRSF1-Pol II interactions at PASs.
• SRSF1 reduces Pol II elongation and limits transcription readthrough, indicating co-transcriptional regulation.

Conclusions:

• SRSF1 regulates PAS selection through both direct RNA binding and U1 snRNP-dependent coordination with Pol II.
• SRSF1 shapes RNA isoform determination beyond its canonical splicing role.
• These findings reveal a novel mechanism of gene expression regulation impacting RNA processing and potentially disease states like cancer.