Elucidating the Role of CaMKK in Cell Cycle and Cell Fate Using a C. elegans Model

摘要

The mammalian calmodulin-dependent protein kinase kinases (CaMKKs) have been shown to phosphorylate and activate the calmodulin-dependent protein kinases I and IV (CaMKI, CaMKIV), leading to transcription of a variety of genes important in cell cycle regulation. Using a C. elegans homologue (ceCaMKK), we are investigating the importance of this proposed cascade to cell cycle, cell fate and development in the context of a well defined multicellular organism. By generating transgenic worms with reporter proteins controlled by the ceCaMKK promoter, gene expression has been demonstrated in the excretory cell, vulval muscle cells and several neurons of adult hermaphrodites, in the hypodermal cells of L1/L2 larvae, and in several male-specific tail cells. To examine this pathway biochemically, we have cloned the ceCaMKK and ceCaMKI cDNAs, and produced recombinant proteins by prokaryotic expression methods. Both mammalian and C elegans CaMKKs can phosphorylate either species' CaMKI homolog specifically on the acitvation loop (T177 in human, T179 in C elegans) in vitro. These results indicate a functional homology between the mammalian and C. elegans calmodulin dependent kinases, and demonstrate the existance of a calmodulin dependent kinase cascade in the worm. Further work remains to reveal the biological functions of this signaling.