Trans-acting factors regulate the expression of CD44 splice variants

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• CD44 variant isoforms (CD44v) are crucial in development, adult tissues, and metastasis.
• CD44v differ from CD44 standard (CD44s) via alternative splicing of variant exon sequences.

Purpose of the Study:

• To investigate the mechanisms controlling alternative splicing of CD44 variant exons.
• To identify trans-acting factors involved in CD44 splicing regulation.

Main Methods:

• Cell fusion experiments, including stable cell hybrids and transient interspecies heterokaryons.
• Analysis of CD44 splicing patterns in various cell lines, including carcinoma cells.

Main Results:

• Cell fusion experiments demonstrated cell-type specific trans-acting factors that recruit CD44 variant exon sequences.
• A dominant mechanism for variant exon inclusion was observed in stable cell hybrids.
• Human keratinocyte CD44 splicing ability was transferred to rat fibroblast nuclei in heterokaryons.
• Complex splice patterns suggest multiple factors, including positively acting factors and exon-specific selectors.
• A pancreatic carcinoma cell line failed to transfer its splice pattern, suggesting mutation-based control.

Conclusions:

• Alternative splicing of CD44 variant exons is regulated by trans-acting factors.
• Splicing regulation involves factors acting in a 3' to 5' direction and additional exon-specific factors.
• Tumor-specific CD44 splicing may result from mutations in cis-acting recognition sites.