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Peptidyl prolyl isomerase (PIN1) regulates the functional activity of a subset of phosphoproteins through binding to phosphorylated Ser/Thr-Pro motifs and subsequently isomerization of the phosphorylated bonds. Interestingly, PIN1 is overexpressed in many types of malignancies including breast, prostate, lung and colon cancers. However, its oncogenic functions have not been fully elucidated. Here, we report that PIN1 directly interacts with hypoxia-inducible factor (HIF)-1α in human colon cancer (HCT116) cells. PIN1 binding to HIF-1α occurred in a phosphorylation-dependent manner. We also found that PIN1 interacted with HIF-1α at both exogenous and endogenous levels. Notably, PIN1 binding stabilized the HIF-1α protein, given that their levels were significantly increased under hypoxic conditions. The stabilization of HIF-1α resulted in increased transcriptional activity, consequently upregulating expression of vascular endothelial growth factor, a major contributor to angiogenesis. Silencing of PIN1 or pharmacologic inhibition of its activity abrogated the angiogenesis. By utilizing a bioluminescence imaging technique, we were able to demonstrate that PIN1 inhibition dramatically reduced the tumor volume in a subcutaneous mouse xenograft model and angiogenesis as well as hypoxia-induced transcriptional activity of HIF-1α. These results suggest that PIN1 interacting with HIF-1α is a potential cancer chemopreventive and therapeutic target.

Generating artificial protein assemblies with complex shapes requires a method for connecting protein components with stable and predictable structures. Currently available methods for creating rigid protein assemblies rely on either complicated calculations or extensive trial and error. We describe a simple and efficient method for connecting two proteins via a fused alpha helix that is formed by joining two preexisting helices into a single extended helix. Because the end-to-end ligation of helices does not guarantee the formation of a continuous helix, we superimposed 1–2 turns of pairs of connecting helices by using a molecular graphics program. Then, we chose amino acids from the two natural sequences that would stabilize the connecting helix. This “shared helix method” is highly efficient. All the designed proteins that could be produced in Escherichia coli were readily crystallized and had the expected fusion structures. To prove the usefulness of this method, we produced two novel repeat proteins by assembling several copies of natural or artificial proteins with alpha helices at both termini. Their crystal structures demonstrated the successful assembly of the repeating units with the intended curved shapes. We propose that this method could dramatically expand the available repertoire of natural repeat proteins.

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Purpose of review This review focuses on our current understanding of fate decisions in bipotent megakaryocyte-erythroid progenitors (MEPs). Although extensive research has been carried out over decades, our understanding of how MEP commit to the erythroid versus megakaryocyte fate remains unclear. Recent findings We discuss the isolation of primary human MEP, and focus on gene expression patterns, epigenetics, transcription factors and extrinsic factors that have been implicated in MEP fate determination. We conclude with an overview of the open debates in the field of MEP biology. Summary Understanding MEP fate is important because defects in megakaryocyte and erythrocyte development lead to disease states such as anaemia, thrombocytopenia and leukaemia. MEP also represent a model system for studying fundamental principles underlying cell fate decisions of bipotent and pluripotent progenitors, such that discoveries in MEP are broadly applicable to stem/progenitor cell biology.