The secretion and extracellular transport of Wnt protein are thought to be well-regulated processes. Wnt is known to be acylated with palmitic acid at a conserved cysteine residue (Cys77 in murine Wnt-3a), and this residue appears to be required for the control of extracellular transport. Here, we show that murine Wnt-3a is also acylated at a conserved serine residue (Ser209). Of note, we demonstrated that this residue is modified with a monounsaturated fatty acid, palmitoleic acid. Wnt-3a defective in acylation at Ser209 is not secreted from cells in culture or in Xenopus embryos, but it is retained in the endoplasmic reticulum (ER). Furthermore, Porcupine, a protein with structural similarities to membrane-bound O-acyltransferases, is required for Ser209-dependent acylation, as well as for Wnt-3a transport from the ER for secretion. These results strongly suggest that Wnt protein requires a particular lipid modification for proper intracellular transport during the secretory process.

Clock proteins govern circadian physiology and their function is regulated by various mechanisms. Here we demonstrate that Casein kinase (CK)-2alpha phosphorylates the core circadian regulator BMAL1. Gene silencing of CK2alpha or mutation of the highly conserved CK2-phosphorylation site in BMAL1, Ser90, result in impaired nuclear BMAL1 accumulation and disruption of clock function. Notably, phosphorylation at Ser90 follows a rhythmic pattern. These findings reveal that CK2 is an essential regulator of the mammalian circadian system.

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