The ciliary protein cystin forms a regulatory complex with necdin to modulate Myc expression

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Cystin, a novel cilia-associated protein, is disrupted in the cpk mouse model of autosomal recessive polycystic kidney disease (ARPKD).
• Myc gene overexpression is observed in ARPKD animal models and is implicated in renal cyst development.

Purpose of the Study:

• To investigate the interaction between cystin and necdin, a protein known to modulate Myc expression.
• To elucidate the role of the cystin-necdin complex in regulating Myc expression and its potential contribution to ARPKD pathogenesis.

Main Methods:

• Yeast two-hybrid screening to identify interacting partners of cystin.
• Deletion mapping to determine interaction domains between cystin and necdin.
• Luciferase reporter assays to assess promoter activity.
• Chromatin immunoprecipitation and electrophoretic mobility shift assays to confirm physical interactions.

Main Results:

• Necdin was identified as a cystin-interacting protein.
• Both cystin and necdin physically interact with the Myc P1 promoter.
• Necdin activates Myc P1 promoter activity, while cystin shows modest activation.
• Co-transfection of cystin abrogates necdin's activation of the Myc P1 promoter, suggesting a regulatory role.

Conclusions:

• Cystin and necdin form a regulatory complex that physically interacts with the Myc P1 promoter.
• Dysregulation of the cystin-necdin complex may lead to Myc overexpression in ARPKD.
• c-Myc, regulated by this complex, likely contributes to cystogenesis in the cpk mouse model of ARPKD.