CLPTM1L is a GPI-anchoring pathway component targeted by HCMV

Area of Science:

• Molecular Biology
• Immunology
• Virology

Background:

• The glycosylphosphatidylinositol (GPI)-anchoring pathway is crucial for cell development and immune responses.
• MHC Class I Polypeptide-related Sequence A (MICA) is a stress-induced ligand often downregulated by human cytomegalovirus (HCMV) to evade immune detection.
• The prevalent MICA*008 allele uses an unknown pathway for GPI-anchoring.

Purpose of the Study:

• To identify the uncharacterized GPI-anchoring pathway component responsible for MICA*008 anchoring.
• To elucidate the mechanism by which HCMV downregulates MICA*008 during infection.
• To investigate the role of the identified component in the expression of other GPI-anchored proteins.

Main Methods:

• Protein identification and characterization.
• Viral infection assays using HCMV.
• Western blotting and gene silencing techniques to assess protein expression.
• Co-immunoprecipitation to study protein interactions.

Main Results:

• Cleft lip and palate transmembrane protein 1-like protein (CLPTM1L) was identified as a novel component of the GPI-anchoring pathway.
• HCMV protein US9 was shown to downregulate MICA*008 expression through CLPTM1L during infection.
• CLPTM1L-dependent expression was observed for some GPI-anchored proteins (CD109, CD59, MELTF) but not others (ULBP2, ULBP3).
• MELTF was also found to be downregulated by US9 via CLPTM1L during HCMV infection.
• CLPTM1L's function appears to depend on its interaction with a free form of PIG-T, a component of the GPI transamidase complex.
• US9 inhibits the CLPTM1L-PIG-T interaction, leading to the downregulation of CLPTM1L-dependent proteins.

Conclusions:

• CLPTM1L is a newly identified component of the GPI-anchoring pathway.
• HCMV utilizes CLPTM1L to downregulate key immune-interacting proteins like MICA*008 and MELTF.
• The HCMV protein US9 targets the interaction between CLPTM1L and PIG-T to disrupt GPI-anchoring and evade immune surveillance.