Characterization of the disease-causing mechanism of KIF3B mutations from ciliopathy patients

Area of Science:

• Molecular biology
• Cell biology
• Genetics

Background:

• Kinesin-2 motor (KIF3A/KIF3B with KAP3) is crucial for intraflagellar transport, ciliogenesis, and ciliary function.
• Point mutations in KIF3B (E250Q, L523P, A334T) are linked to human retinal atrophy and other ciliopathies, but their molecular basis is unknown.

Purpose of the Study:

• To characterize the molecular mechanisms underlying disease phenotypes caused by KIF3B mutations.
• To investigate the effects of specific KIF3B mutations on kinesin-2 complex assembly, microtubule interaction, and motor function.

Main Methods:

• Utilized KIF3A/KIF3B knockout 3T3 cells lacking cilia.
• Reexpressed wildtype and mutant KIF3B constructs (E250Q, L523P, A334T).
• Employed fluorescent tagging and cell-based assays to assess ciliogenesis, microtubule binding, motility, and Golgi dispersal.

Main Results:

• KIF3B(E250Q) and KIF3B(L523P) failed to rescue ciliogenesis; KIF3B(A334T) partially restored it.
• E250Q is a rigor mutation, binding microtubules tightly. L523P impaired motility without affecting complex assembly. A334T showed reduced expression and impaired high-load cargo transport.
• The study elucidates distinct molecular defects for each disease-associated KIF3B mutation.

Conclusions:

• Disease-causing mutations in KIF3B disrupt kinesin-2 function through various mechanisms, including impaired motility and reduced expression.
• These findings provide molecular insights into ciliopathies associated with KIF3B dysfunction.