Cell surface engineering with functional polymers is an effective strategy to modulate cell activity. Here, a bio‐palladium catalyzed polymerization strategy was developed for in situ synthesis of conjugated polymers on living cell surfaces. Through Sonagashira polymerization, photoactive polyphenyleneethynylene (PPE) is synthesized on the cell surface via cell‐generated bio‐Pd catalyst. The in situ formed PPE is identified by excellent light‐harvest capacity and blue fluorescence on the surfaces of E. coli and C. pyrenoidosa. Besides imaging microbes for tracing the polymerization process, PPE also exhibits enhanced antibacterial activity against E. coli. It can also augment the ATP synthesis of C. pyrenoidosa through enlarging the light absorption and accelerating the cyclic electron transport of the algae. With this bio‐metal catalyzed polymerization method, functional polymers can be synthesized in situ on the living cell surface.

Dually targeted mitochondrial proteins usually possess an unconventional mitochondrial targeting sequence (MTS), which makes them difficult to predict by current bioinformatics approaches. Human apurinic/apyrimidinic endonuclease (APE1) plays a central role in the cellular response to oxidative stress. It is a dually targeted protein preferentially residing in the nucleus with conditional distribution in the mitochondria. However, the mitochondrial translocation mechanism of APE1 is not well characterized because it harbors an unconventional MTS that is difficult to predict by bioinformatics analysis. Two experimental approaches were combined in this study to identify the MTS of APE1. First, the interactions between the peptides from APE1 and the three purified translocase receptors of the outer mitochondrial membrane (Tom) were evaluated using a peptide array screen. Consequently, the intracellular distribution of green fluorescent protein-tagged, truncated, or mutated APE1 proteins was traced by tag detection. The results demonstrated that the only MTS of APE1 is harbored within residues 289 -318 in the C terminus, which is normally masked by the intact N-terminal structure. As a dually targeted mitochondrial protein, APE1 possesses a special distribution pattern of different subcellular targeting signals, the identification of which sheds light on future prediction of MTSs.Human APE1 (apurinic/apyrimidinic endonuclease) is an important multifunctional protein that plays a central role in the cellular response to oxidative stress. The two major activities of APE1 are DNA repair and redox regulation of transcriptional factors. On one hand, APE1 functions as a critical ratelimiting enzyme in DNA base excision repair and accounts for nearly all of the AP site incision activities in cell extracts (1). On the other hand, APE1 also exerts unique redox activity to regulate the DNA binding affinity of certain transcriptional factors by controlling the redox status of their DNA-binding domain (2). Inhibition of the redox function of APE1 blocks murine endothelial cell growth and angiogenesis and also blocks the growth of human tumor cell lines (3). The biological importance of APE1 is highlighted by the finding that APE1 knockout mice exhibit an embryonic lethal phenotype (4). Although APE1 has long been labeled as a nuclear protein, a growing body of evidence has shown that the subcellular distribution of APE1 can be cytoplasmic in some cell types with high metabolic or proliferative rates, with predominant localization in the mitochondria and the endoplasmic reticulum (5-7). Recent mitochondrial proteomic studies have further confirmed the existence of APE1 in the mitochondria (8). Considering the importance of the mitochondria in cellular response to oxidative stress, the roles of APE1 in the mitochondria have been extensively investigated.

Apurinic/apyrimidinic endonuclease1 (APE1), which has the dual functions of DNA repair and redox regulation, is considered to be a promising potential target in cancer treatment. Microarray and qRT-PCR were used to confirm the change of miRNA followed by analysis with comprehensive bioinformatics-based analysis. Both microarray and qRT-PCR demonstrated that 13 microRNAs (miRNAs) were significantly changed (>2-fold) in APE1 knockdown HOS cells; seven of them (hsa-miR-451, hsa-miR-1290, hsa-miR-765, hsa-miR-483-5p, hsa-miR-513a-5p, hsa-miR-129-5p and hsa-miR-31) were up-regulated and the other six (hsa-miR-29b, hsa-miR-197, has-let-7b, hsa-miR-324-5p, hsa-let-7i and hsa-miR-484) were down-regulated. Furthermore, pathway analysis showed that these miRNAs and their target genes affected by the expression of APE1 were involved in pathways relating to developmental processes, regulation of cellular processes, cell signaling (such as TGF-β, Wnt, MAPK and the p53 signaling pathway) and cancers. There are putative binding sites of NF-κB, p53, HIF-1α, AP-1, PEBP2, ATF, NF-Y, Pax-2,CREB and c-Myb in the promoters of several down regulated miRNAs, indicating that APE1 may regulate miRNAs via transcription factors. Our data suggest that our understanding of the biological functions of APE1 will inevitably expand due to the novel pathways that APE1 uses to regulate gene expression through miRNAs.