Background: Secreted PCSK9 regulates LDL levels in plasma by mediating degradation of hepatic LDL receptors.Results: LDL binds to PCSK9 in human plasma and in vitro and inhibits PCSK9 binding to cell surface LDL receptors.Conclusion: A large proportion of circulating PCSK9 is bound to LDL in humans.Significance: Regulatory mechanisms that affect activity of secreted PCSK9 represent novel targets for cholesterol-lowering therapies.

The chromosome passenger complex (CPC) consists of Aurora-B kinase and several other subunits. One of these, incenp, binds Aurora-B and regulates its kinase activity. During Xenopus oocyte maturation, incenp accumulates through translation, contributing to aurora-b activation. A previous study has demonstrated that inhibition of incenp translation during oocyte maturation diminishes aurora-b activation but does not interfere with oocyte maturation, characterized by normal maturation-specific cyclin-b phosphorylation, degradation, and resynthesis. Here we have extended these findings, showing that inhibition of incenp translation during oocyte maturation did not interfere with meiosis I or II, as indicated by the normal emission of the first polar body and metaphase II arrest, followed by the successful emission of the second polar body upon parthenogenetic egg activation. Most importantly, however, when transferred to host frogs and subsequently ovulated, the incenp-deficient eggs were fertilized but failed to undergo mitotic cleavage. Thus, translation of incenp during oocyte maturation appears to be part of oocyte cytoplasmic maturation, preparing the egg for the rapid mitosis following fertilization.

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