Protein Kinase X Activates Ureteric Bud Branching Morphogenesis in Developing Mouse Metanephric Kidney

Abstract

The human protein kinase X (PRKX) gene was identified previously as a cAMP-dependent serine/threonine kinase that is aberrantly expressed in autosomal dominant polycystic disease kidneys and normally expressed in fetal kidneys. The PRKX kinase belongs to a serine/threonine kinase family that is phylogenetically and functionally distinct from classical protein kinase A kinases. Expression of PRKX activates cAMP-dependent renal epithelial cell migration and tubular morphogenesis in cell culture, suggesting that it might regulate branching growth of the collecting duct system in the fetal kidney. With the use of a mouse embryonic kidney organ culture system that recapitulates early kidney development in vitro, it is demonstrated that lentiviral vector-driven expression of a constitutively active, cAMP-independent PRKX in the ureteric bud epithelium stimulates branching morphogenesis and results in a 2.5-fold increase in glomerular number. These results suggest that PRKX stimulates epithelial branching morphogenesis by activating cell migration and support a role for this kinase in the regulation of nephrogenesis and of collecting system development in the fetal kidney.

Cystic Disease of the Kidney

“…This was first confirmed by the observation that PC-1, PC-2, and NPHP-1 could all be colocalized by immunofluorescence and co-immunoprecipitated in the same complex with structural and signaling proteins of focal adhesion and cell-cell adherens junction protein complexes (44,58). Subsequent analyses have demonstrated that flotillin, specific receptor protein tyrosine phosphatases, FC, and a variety of actin-binding proteins can also be found in these multiprotein complexes (19,59,60). Normal PC-1/PC-2/FC-1/NPHP multiprotein complexes are likely dynamic.…”

“…Unlike PKA, however, PRKX has a restricted expression pattern in the kidney, specifically colocalizing with and phosphorylating the intracellular C-terminal domain of PC-1 at S4161. Importantly, PRKX can reverse the cystic inductive effects of PC-1 inactivation in mouse kidneys in organ culture (19). Other proliferative ligands have been identified and proposed as contributing to PKD, including lactosylceramide, an additional unidentified neutral lipid factor, and various inflammatory cytokines (15,20).…”

Shaping up for action

“…For example, using specific promoters to light up the UB, this approach was used to determine the pattern of UB branching, and to reveal the cellular and molecular mechanisms that underpin branching. [127][128][129][130] Further innovations using viral vectors 131,132 or small interfering RNAs (siRNA) 133,134 for efficient gene knockdown allow functional analyses to performed rapidly.…”

Regulation of cAMP-dependent Protein Kinases

“…It was found to be crucial for macrophage and granulocyte maturation (9, 10). PrKX was shown to be involved in renal development, regulating epithelial cell migration, ureteric bud branching, and induction of glomeruli formation (8,(11)(12)(13).C␣ and human PrKX differ by their selective holoenzyme formation in living cells, as PrKX is inhibited only by RI␣, but not by RII␣ (14,15). Here, we have tested all four human R subunits for the first time side by side and show that this so far unique property of RI over RII preference with respect to autoinhibition appears to be an evolutionarily conserved feature of PrKX and at least four of its orthologs (Mus musculus Pkare, Drosophila melanogaster DC2, Trypanosoma brucei PKAC3, human PrKY), and possibly also Caenorhabditis elegans F47F2.1b.…”

“…It was found to be crucial for macrophage and granulocyte maturation (9, 10). PrKX was shown to be involved in renal development, regulating epithelial cell migration, ureteric bud branching, and induction of glomeruli formation (8,(11)(12)(13).…”