Kidney Week

Abstract: SA-PO467

Elevated Calcium/Calmodulin-Dependent Protein Kinase IV (CaMK4) Promotes mTOR-Dependent Cell Proliferation in ADPKD

Session Information

• Cystic Kidney Diseases: Basic/Translational
  November 09, 2019 | Location: Exhibit Hall, Walter E. Washington Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Genetic Diseases of the Kidneys

• 1001 Genetic Diseases of the Kidneys: Cystic

Authors

• Zhang, Yan, University of Kansas Medical Center, Kansas City, Kansas, United States

Yan Zhang,

• Daniel, Emily A., University of Kansas Medical Center, Kansas City, Kansas, United States

Emily A. Daniel,

• Dai, Yuqiao, University of Kansas Medical Center, Kansas City, Kansas, United States

Yuqiao Dai,

• Reif, Gail, University of Kansas Medical Center, Kansas City, Kansas, United States

Gail Reif,

• Wallace, Darren P., University of Kansas Medical Center, Kansas City, Kansas, United States

Darren P. Wallace,

Background

Mammalian target of rapamycin (mTOR), a central integration site for pathways involved in cell growth and proliferation, is abnormally activated in cyst-lining cells in ADPKD. mTOR inhibition reduces cell proliferation and PKD progression in rodents; however, the therapeutic value of targeting mTOR with rapalogues in ADPKD patients remains unclear due to dose-limiting side effects. The development of new therapies requires a better understanding of pathways responsible for aberrant mTOR activation in cystic epithelial cells. Calcium/calmodulin-dependent kinase type IV (CaM4) stimulates mTOR signaling in various cell types including hepatic cancer cells and immune cells; however, the role of CaMK4 on mTOR signaling and cyst growth in PKD has not been examined.

Methods

CaMK4 levels were measured in primary ADPKD and normal human kidney (NHK) cells, and in Pkd1^RC/RC (slow onset), Pkd1^RC/RC; Pkd2^+/- (rapid onset) and normal mouse kidneys by Western blot analysis. The effect of KN-93, a CaMK4 inhibitor, on mTOR signaling was evaluated in ADPKD cells. To determine if CaMK4 regulation of mTOR was dependent on the LKB1/AMPK pathway, we tested KN-93 on renal cells with an inducible knockout of Lkb1. pcy/pcy mice, a well-characterized PKD model, received 10 mg/kg KN-93 every day for one week to determine the effect of CaMK4 inhibition on renal mTOR signaling.

Results

CaMK4 levels were 2.5-fold higher in human ADPKD cells compared to NHK cells. Renal CaMK4 levels were also elevated in Pkd1^RC/RC and Pkd1^RC/RC; Pkd2^+/- mouse kidneys compared to age-matched normal littermates. Incubation with KN-93 decreased P-mTOR, P-S6K and P-S6, downstream targets of mTOR, and proliferation of ADPKD cells. mTOR inhibition by KN-93 was not affected by LKB1 knockout in renal epithelial cells, consistent with a direct effect of CaMK4 on the mTOR complex. CaMK4 inhibition with KN-93 decreased renal levels of P-S6 in pcy/pcy mice.

Conclusion

Elevated CaMK4 promotes mTOR signaling in PKD kidneys and may be a potential target to reduce mTOR-dependent cell proliferation and cyst growth.

Funding

• NIDDK Support