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The Impact of Meprin A‐Mediated Cleavage on the Function of the Catalytic Subunit of Protein Kinase A (PKA Cβ1)

The AGC family of protein kinases are serine/threonine kinases that regulate a variety of cell signaling pathways, ranging from growth factor‐mediated regulation of cell cycle and survival to modulation of extracellular matrix metabolism (ECM) in kidney cells. Meprins are zinc metalloproteases that are abundantly expressed in the brush border membranes of proximal kidney tubules. Meprins have been implicated in the progression kidney disease (e.g., ischemia‐reperfusion‐induced acute kidney injury and diabetic nephropathy (DN)). Under certain pathological conditions, meprins are redistributed from the brush‐border membranes to the cytosol and basolateral membranes, where they are able to cleave select proteins. Identified kidney meprin targets include two members of the AGC kinase family, namely the catalytic subunit of protein kinase A (PKA C) and protein kinase C (PKC). Proteolytic processing of PKA C by meprins is isoform specific, both with respect to the PKA C isoform being cleaved and the meprin isoform. Additionally, we found that the beta isoform of PKA C (PKA Cβ1) was differentially cleaved by meprin A and meprin B. While meprin B cleaves PKA Cβ1 at two sites (one between K22/A23 in the N‐terminal tail and another between E322/E323 in the C‐terminal tail), meprin A cleaves PKA Cβ1 at only one site (between R29/K30 in the N‐terminal tail).