Proteasome Phosphorylation and Activation by PKA Protects against Cardiac Remodeling in Mice Subjected to Myocardial Infarction
Authors: Wang Xuejun , Wu Penglong , Pan Bo , Parajuli Nirmal , Lewno Megan , Liu Jinbao 
Published: June 2021

Protein kinase A (PKA) has been extensively studied for its (patho)physiological roles in the cardiovascular system, resulting in a comprehensive understanding of PKA‐mediated regulation of myofilament functioning, ion channel activities, calcium handling, energy metabolism, as well as gene expression and protein synthesis. By contrast, very little is known about PKA's regulation of protein degradation and the (patho)physiological significance of this regulation. A recent study demonstrates in cultured non‐cardiac cells that PKA activates the proteasome (Psm) by phosphorylating Ser14 of Rpn6/PSMD11 (a non‐ATPase regulatory subunit of the 26S Psm), which disputes an earlier report that Ser120 of Rpt6/PSMC5 was the phosphosite for PKA to activate the Psm. Moreover, the in vivo (patho)physiological relevance of Psm phosphoregulation by PKA or by any kinases has not been established. To fill these critical gaps, we conducted the following studies. First, we confirmed in cultured cardiomyocytes that elevating cAMP with forskolin increased the Ser14 phosphorylation of Rpn6 (p‐Rpn6) in a PKA‐dependent manner, which was associated with UPS enhancement as evidenced by the shortened half‐life of GFPu, a surrogate UPS substrate. Second, we created two mouse models whose gene encoding Rpn6/Psmd11 was modified in such a manner that Ser14 of Rpn6 is mutated to either Ala (S14A) or Asp (S14D) to block or mimic PKA‐mediated phosphorylation, respectively. Increases in myocardial p‐Rpn6 and in 26S Psm activities by PKA activation were observed in wild type (WT) mice but not in the S14A knock‐in mice and, conversely, the S14D mice showed significantly higher basal myocardial 26S Psm activities than gender‐ and age‐matched WT mice. These provide the first in vivo demonstration that Ser14 of Rpn6 is the primary, if not the only, phosphosite responsible for PKA activation of the 26S Psm. Third, female S14A, S14D, and age‐matched WT mice were subjected to coronary artery ligation to produce myocardial infarction (MI). Serial echocardiography (echo) at 2, 4, and 8 weeks post‐MI revealed no discernible difference in any echo parameters among the three MI groups at 2 weeks post‐MI; however, at 4 weeks, the S14D MI group showed significantly less LV chamber dilatation (vs. WT‐MI and S14A MI groups), and by 8 weeks, the reduction of fractional shortening and ejection fraction became more severe in the S14A MI group than in the other two MI groups, indicating that Psm phosphoregulation by PKA protects against post‐MI cardiac remodeling and malfunction. Taken together, the present study has unequivocally established a cardioprotective role for Psm phosphoregulation by PKA in mice subjected to myocardial ischemia.Support or Funding InformationThis work is in part supported by NIH grants HL072166, HL085629, and HL131667.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.