Investigating the functional link between TMEM165 and SPCA1

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• TMEM165 (Uncharacterized Protein Family 0016) is linked to human glycosylation diseases and Golgi abnormalities.
• TMEM165 is known to degrade with high manganese levels.
• SPCA1 is a Golgi-localized Ca2+/Mn2+ P-type ATPase pump.

Purpose of the Study:

• To investigate the functional relationship between TMEM165 and SPCA1.
• To determine how SPCA1 function affects TMEM165 stability and localization.
• To elucidate the role of manganese transport in TMEM165 regulation.

Main Methods:

• Analysis of TMEM165 levels in SPCA1-deficient Hap1 cells.
• Lysosomal degradation assays.
• Complementation studies using wild-type and mutant SPCA1.
• Overexpression of SERCA2b.

Main Results:

• SPCA1 deficiency leads to near-complete loss of TMEM165, with TMEM165 constitutively degraded in lysosomes.
• TMEM165 abundance is directly dependent on SPCA1's manganese pumping activity into the Golgi lumen.
• A specific SPCA1 mutant (Q747A) favoring Mn2+ transport rescues TMEM165 abundance and localization.
• Overexpression of SERCA2b also rescues TMEM165 expression.

Conclusions:

• TMEM165 expression is tightly regulated by SPCA1 function, particularly its ability to transport manganese.
• Manganese transport into the Golgi lumen is critical for maintaining TMEM165 stability.
• This study establishes a direct functional link between SPCA1 and TMEM165, relevant to glycosylation disorders.