A Molecular Mechanism Underlying Genotype-Specific Intrahepatic Cholestasis Resulting From MYO5B Mutations

Area of Science:

• Hepatology
• Molecular Biology
• Genetics

Background:

• Progressive Familial Intrahepatic Cholestasis type 6 (PFIC6) is linked to MYO5B mutations, but the mechanism remains unclear.
• The specific genotype-phenotype correlation for MYO5B mutations in PFIC6 is not understood.
• The role of myosin Vb (myoVb) in canalicular protein localization requires elucidation.

Purpose of the Study:

• To investigate if MYO5B mutations cause PFIC6 through myoVb loss-of-function or altered protein function.
• To determine the mechanism by which MYO5B mutations lead to defects in canalicular protein localization.
• To assess the impact of patient-specific myoVb mutants on hepatocyte function.

Main Methods:

• Generated and analyzed MYO5B knockout models in vitro and in vivo.
• Expressed patient-specific myoVb mutants, including tail-domain only and motor domain-deficient variants.
• Investigated the interaction between myoVb mutants and rab11a at the trans-Golgi Network/recycling endosome interface.

Main Results:

• A specific missense mutation (P660L) in myoVb caused intracellular accumulation of bile canalicular proteins.
• MYO5B knockout did not result in canalicular localization defects, suggesting loss-of-function is not the cause.
• Motor domain-deficient myoVb inhibited apical recycling endosome formation and canalicular protein localization in a rab11a-dependent manner.

Conclusions:

• MYO5B mutations causing PFIC6 act through a rab11a-mediated toxic gain-of-function, not myoVb loss.
• The mechanism involves disruption at the trans-Golgi Network/recycling endosome interface.
• This explains the association of specific MYO5B motor domain mutations with PFIC6, while null mutations are not linked.