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Kidney Week

Abstract: PO1234

Species-Specific Differences in FPC-CTD Trafficking: Implications for Differential Activation of Intracellular Signaling Pathways

Session Information

Category: Genetic Diseases of the Kidneys

  • 1001 Genetic Diseases of the Kidneys: Cystic

Authors

  • Yang, Chaozhe, Children's National Research Institute, Washington, District of Columbia, United States
  • Harafuji, Naoe, Children's National Research Institute, Washington, District of Columbia, United States
  • Odinakachukwu, Maryanne, Children's National Research Institute, Washington, District of Columbia, United States
  • Caldovic, Ljubica, Children's National Research Institute, Washington, District of Columbia, United States
  • Bebok, Zsuzsanna M., The University of Alabama at Birmingham Department of Cell Developmental and Integrative Biology, Birmingham, Alabama, United States
  • Guay-Woodford, Lisa M., Children's National Research Institute, Washington, District of Columbia, United States
Background

ARPKD (MIM 263200) is caused by mutations in PKHD1, which encodes FPC. But, orthologous mouse Pkhd1 models either have no renal cystic disease or very mild PCT dilatation. We previously showed that MYC/Myc is overexpressed in human ARPKD and mouse Cys1cpk/cpk (cpk) kidneys, but not in several Pkhd1 mutants. We also showed that expression of the intracellular carboxy-terminus of mouse FPC (mFPC-CTD), but not human (hFPC-CTD), activates the Myc/MYC P1 promoter (ASN 2020). The current study focused on: 1) the intracellular trafficking of mFPC-CTD and hFPC-CTD, and 2) activation of the Src/STAT3 signaling pathway, linked to hFPC-CTD (Strubl 2020), in a mouse Pkhd1 mutant lacking FPC-CTD and in the cpk mouse model of ARPKD, with and without Cys1 rescue.

Methods

Comparative informatic analysis. Immortalized mouse CCD (mCCD) and human (hCCD) cell lines stably expressing mFPC-CTD and hFPC-CTD, respectively. Kidneys from cpk, Cys1-rescued cpk, and Pkhd1del6/del67 (del67) mutant mice; western blot and immunofluorescence.

Results

FPC-CTD is the least conserved domain, with 55% identity between human-mouse CTDs, compared with 73% identity across the full-length FPC. The CTD is unique, with an AA-sequence not found in other terrestrial vertebrate proteins. In stable cell lines, mFPC-CTD localized to both nuclei and cilia, whereas hFPC-CTD primarily localized to the apical membrane. In non-cystic del67 kidneys (lacking FPC-CTD), pSTAT3Y705 and c-Myc levels were similar to wild-type controls. In cpk kidneys, pSTAT3Y705 and c-Myc were upregulated, but their levels in Cys1-rescued cpk kidneys (Yang 2021) were comparable to wild-type.

Conclusion

Differences in intracellular trafficking of mFPC-CTD and hFPC-CTD may explain the species-specific differences in Myc/MYC P1 promoter activation. Distinct subcellular localizations may reflect divergence in the functional evolution of human and mouse FPC-CTD, with mFPC-CTD evolving to function as a nuclear regulatory factor, whereas hFPC-CTD functions as a membrane-associated signaling regulator of Src-STAT3. Activation of Src-STAT3 signaling and Myc upregulation are signatures of cystic epithelia, suggesting that renoprotective mechanisms in FPC-deficient mouse kidneys may modulate these pathways.

Funding

  • NIDDK Support