Developing organisms must coordinate diverse cellular processes such as cell proliferation, growth, differentiation, and death. The coordination of growth and death processes ultimately governs cell number and is critical in the maintenance of adult tissues, as deregulated proliferation coupled with a defect in cell death can lead to tumorigenesis.
While the balance of these processes is important for the organism on the whole, regulated coordination of the molecular pathways involved in cell proliferation and cell death also occurs at the cellular level. As we learn more about the mechanisms controlling proliferation and death, we are beginning to see direct molecular connections through factors involved in both processes. Specifically, a subset of molecules responsible for the progression of the cell cycle have been shown to interact directly with and impose regulatory signals on factors that regulate apoptosis, or programmed cell death.
The studies presented here focus on one such factor, XLX, a Xenopus laevis Inhibitor of Apoptosis (IAP) family member. We have cloned XLX and found that it shares many characteristics, such as caspase inhibition and autoubiquitylation, with other IAPs. However, XLX is unique in its post-translational regulation. Specifically, we show that XLX is phosphorylated during meiosis and that the kinases responsible for XLX phosphorylation belong to the MAPK and MPF pathways. Although the biological consequence of this phosphorylation remains to be further clarified, we show that caspase-dependent cleavage of XLX is altered when XLX is phosphorylated.
In addition to furthering our understanding of the post-translational regulation of an IAP, these findings reveal a novel link between cell cycle regulated protein kinases and a component potentially involved in apoptosis.
