Cyclin-Dependent Kinase 16/PCTAIRE Kinase 1 Is Activated by Cyclin Y and Is Essential for Spermatogenesis

Abstract

Cyclin-dependent kinase 16 (CDK16, PCTK1) is a poorly characterized protein kinase, highly expressed in the testis and the brain. Here, we report that CDK16 is activated by membrane-associated cyclin Y (CCNY). Treatment of transfected human cells with the protein kinase A (PKA) activator forskolin blocked, while kinase inhibition promoted, CCNY-dependent targeting of CDK16-green fluorescent protein (GFP) to the cell membrane. CCNY binding to CDK16 required a region upstream of the kinase domain and was found to be inhibited by phosphorylation of serine 153, a potential PKA phosphorylation site. Thus, in contrast to other CDKs, CDK16 is regulated by phosphorylation-controlled cyclin binding. CDK16 isolated from murine testis was unphosphorylated, interacted with CCNY, and exhibited kinase activity. To investigate the function of CDK16 in vivo, we established a conditional knockout allele. Mice lacking CDK16 developed normally, but male mice were infertile. Spermatozoa isolated from their epididymis displayed thinning and elongation of the annulus region, adopted a bent shape, and showed impaired motility. Moreover, CDK16-deficient spermatozoa had malformed heads and excess residual cytoplasm, suggesting a role of CDK16 in spermiation. Thus, CDK16 is a membrane-targeted CDK essential for spermatogenesis.

Orphan kinases turn eccentric

“…15,63,64 By using full-length human CDK16 as a bait in a yeast two-hybrid interaction screen, we have identified several novel interactors, of which CCNY was found to robustly activate CDK16 against MBP. 9 The interaction of CDK16 with CCNY was confirmed in vivo, and the kinase complex isolated from murine testis and brain was found to be active. 9 Similarly, the Caenorhabditis elegans (C. elegans) homolog PCT-1 interacts with CYY-1, the nematode CCNY ortholog.…”

“…9 The interaction of CDK16 with CCNY was confirmed in vivo, and the kinase complex isolated from murine testis and brain was found to be active. 9 Similarly, the Caenorhabditis elegans (C. elegans) homolog PCT-1 interacts with CYY-1, the nematode CCNY ortholog. 65 CCNY is well conserved among eumetazoa, but in contrast to conventional cyclins contains only a single cyclin fold.…”

“…When bound to its activator cyclin Y (CCNY), CDK16 is targeted to the plasma membrane, but this localization has still to be confirmed in vivo. 9 The endogenous protein was, so far, found to be localized in the cytoplasm 14 and the nucleolus of neurons. 15 As discussed further below, CDK16 is phosphorylated at several residues, which regulates its ability to interact with, and become activated by, CCNY.…”

“…2 Some of the CDKs (CDK1, 2, 3, 4, 6) are involved in cell cycle regulation and have been studied intensively for more than 30 y. The majority of the CDK family members, however, do not control proliferation but are involved in other cellular processes, including transcription (CDK7, 8,9,10), translation (CDK1, 11), mRNA processing (CDK10, 11,12,13) or control differentiation and function of neurons (CDK5). [3][4][5] The CDK family counts 26 members, classified as CDK1-20 (there are two CDK11 isoforms, CDK11A and B) and five additional more distant members called CDK-like (CDKL) kinases.…”

“…In Drosophila, CDK14 is essential for development and participates in WNT signaling, 7,8 while the CDK16 homolog PCT-1 plays an important role in motor neurons in nematodes. In mammals, CDK16 is essential for spermatogenesis, 9 suggesting that PFTAIRE/PCTAIRE kinases are involved in many important, yet different, cellular functions. Here, we review PCTAIRE and PFTAIRE kinases and argue that true PCTAIRE kinases, i.e., CDK16 homologs, are restricted to animals, suggesting an essential role in the nervous system.…”