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Limiting Muscle Mass
Skeletal muscle mass changes in response to activity, the availability of nutrients, and pathologic loss of muscle mass are associated with long-term bed rest, cachexia-inducing diseases, and starvation. Hu et al. used overexpression, knockout, and knockdown studies to show that the kinase MNK2 had a negative regulatory role on proteins involved in protein synthesis under atrophy-promoting conditions. This was unexpected because MNK2 is also part of a eukaryotic translation initiation complex and is one of the two isoforms capable of phosphorylating a component of that complex on a site associated with promotion of protein synthesis. The negative regulatory effects on protein synthesis machinery appeared to involve a kinase-independent interaction with mTOR, a master regulator of protein synthesis, and a kinase-dependent regulation of another kinase, SRPK, which had not been previously implicated in regulation of protein synthesis.
