Native and Polyubiquitinated Forms of Dihydroceramide Desaturase Are Differentially Linked to Human Embryonic Kidney...

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Dihydroceramide desaturase (Degs1) has controversial roles in cell survival, with evidence suggesting it can both promote and protect against apoptosis.
• Understanding the molecular mechanisms behind Degs1's opposing functions is crucial for elucidating its role in cell fate determination.

Purpose of the Study:

• To investigate the molecular basis for the opposing roles of dihydroceramide desaturase (Degs1) in cell survival and apoptosis.
• To determine how Degs1 modification, specifically polyubiquitination, influences its function in cellular pathways.

Main Methods:

• Treatment of HEK293T cells with sphingosine kinase inhibitors (SKi, ABC294640) and a Degs1 inhibitor (GT11).
• Analysis of Degs1 polyubiquitination, oxidative stress markers, p38 MAPK, Mdm2 (E3 ligase), and prosurvival pathways (JNK, XBP-1s).
• Assessment of apoptosis and ceramide synthesis in response to inhibitor treatments.

Main Results:

• SKi and fenretinide induced Degs1 polyubiquitination via oxidative stress, p38 MAPK, and Mdm2, leading to activation of prosurvival pathways (p38 MAPK, JNK, XBP-1s).
• ABC294640 did not induce Degs1 polyubiquitination but promoted apoptosis through a Degs1-dependent mechanism involving increased ceramide synthesis.
• Polyubiquitinated Degs1 exhibits a gain of function, activating prosurvival signaling.

Conclusions:

• Degs1 polyubiquitination converts the enzyme from a proapoptotic to a prosurvival factor.
• This modification provides a molecular explanation for the previously observed contradictory functions of Degs1 in cell survival and apoptosis.
• Targeting Degs1 modification could offer therapeutic strategies for diseases involving aberrant cell survival or death.