PAK Kinases Target Sortilin and Modulate Its Sorting
Sortilin is a multifunctional receptor mediating internalization and intracellular transport of multiple ligands via several sorting adaptors. Pallesen et al. (e00411-19) demonstrate that a major sorting site in the cytoplasmic domain of sortilin is part of a binding site for the group A PAK kinases, PAK1 to -3. The study reveals for the first time that PAK kinases have a direct impact on sortilin as they bind and phosphorylate a serine residue positioned in a sorting motif. The authors further show that the phosphorylation reduces adaptor protein affinity and alters its subcellular localization. These findings provide new insight into the mechanisms that regulate sortilin-mediated sorting and add a new aspect to the functional repertoire of PAK kinases.
Xkr8-Mediated Phosphatidylserine Exposure on Apoptotic Germ Cells Is Needed for Spermatogenesis
During spermatogenesis up to 75% of germ cells undergo apoptosis and are cleared by Sertoli cells. In response to apoptotic signals, Xkr8 at plasma membranes scrambles phospholipids, exposing phosphatidylserine. Yamashita et al. (e00402-19) show that Xkr8−/− male mice are infertile due to the inefficient clearance of apoptotic germ cells. Many unengulfed apoptotic cells and cell debris are present in Xkr8−/− testes, suggesting that noxious materials are released from unengulfed apoptotic cells to inhibit spermatogenesis. Alternatively, failure to engulf the apoptotic germ cells may have caused the Sertoli cells to starve and lose their ability to support spermatogenesis.
- Copyright © 2020 American Society for Microbiology.
