Quantitative transcriptomic profiling of branching in a glycosphingolipid biosynthetic pathway

Area of Science:

• Biochemistry
• Cell Biology
• Genetics

Background:

• Cellular regulation of branched biosynthetic pathways, like that for glycosphingolipid (GSL) GM1, is complex.
• Understanding these regulatory mechanisms is crucial for cellular control and function.

Purpose of the Study:

• To investigate the regulatory mechanisms of the GSL GM1 biosynthetic pathway using a novel quantitative phenotype-genotype correlation analysis.
• To identify key regulatory enzymes and their interactions within the GSL biosynthesis pathway.

Main Methods:

• Utilized correlation index-based responsible enzyme gene screening (CIRES), a novel transcriptomic analysis method.
• Analyzed gene expression profiles from multiple B cell lines to correlate enzyme expression with GM1 levels.
• Investigated enzyme localization and complex formation using Golgi apparatus proximity and protein interactions.

Main Results:

• CD77 synthase (CD77Syn) expression negatively correlated with and suppressed GM1 levels, contrary to direct biosynthetic enzymes.
• Catalytically inactive CD77Syn also suppressed GM1, indicating a non-enzymatic regulatory role.
• CD77Syn targets and accelerates the turnover of LacCer synthase (LacCerSyn), a proximal enzyme, by forming a complex in the Golgi apparatus.
• This interaction globally alters GSL species expression.

Conclusions:

• CD77Syn acts as a global regulator of GSL biosynthesis by modulating LacCerSyn activity and stability, rather than through direct substrate consumption.
• Transcriptomic assessment, even revealing unexpected regulatory roles like that of CD77Syn, is a powerful tool for dissecting complex macromolecule biosynthetic pathways.