Polygonatum cyrtonema lectin (PCL), a mannose/sialic acid-binding plant lectin, has recently drawn a rising attention for cancer biologists because PCL bears remarkable anti-tumor activities and thus inducing programmed cell death (PCD) including apoptosis and autophagy in cancer cells. In this review, we focus on exploring the precise molecular mechanisms by which PCL induces cancer cell apoptotic death such as the caspase-dependent pathway, mitochondria-mediated ROS-p38-p53 pathway, Ras-Raf and PI3K-Akt pathways. In addition, we further elucidate that PCL induces cancer cell autophagic death via activating mitochondrial ROS-p38-p53 pathway, as well as via blocking Ras-Raf and PI3K-Akt pathways, suggesting an intricate relationship between autophagic and apoptotic death in PCL-induced cancer cells. In conclusion, these findings may provide a new perspective of Polygonatum cyrtonema lectin (PCL) as a potential anti-tumor drug targeting PCD pathways for future cancer therapeutics.

Polygonatum cyrtonema lectin (PCL) has been drawing rising attention due to its remarkable bioactivities. Whereas, large-scale isolation and purification of PCL from Polygonatum cyrtonema Hua is not feasible due to the extremely low propagation rate of this plant. Herein, an alternative method to produce large amount of PCL by Escherichia coli expression system was proposed, and recombinant Polygonatum cyrtonema lectin (rPCL) was successfully obtained under the optimized conditions (OD600=0.6, 30◦C, 0.5mM IPTG, pH 7.2). Subsequent SDS-PAGE and MALDI-TOF analysis confirmed that the molecular mass of rPCL was approximate to 12 kDa. After further identification of rPCL by Western blot and N-terminal amino acid sequence analysis, the comparisons of hemagglutinating and carbohydrate-binding activities as well as the anti-viral and apoptosis-inducing properties between rPCL and native Polygonatum cyrtonema lectin (nPCL) were made. It was verified that the bioactivities of rPCL were relatively weaker than that of nPCL. Moreover, for future exploring three-dimensional structure and structure–bioactivity relationship of rPCL, circular dichroism and fluorescence spectroscopy, preliminary crystallization and X-ray diffraction were determined. Taken together, these findings provide novel evidence that rPCL could replace nPCL as a potential anti-tumor and anti-viral protein in possible medical application and large-scale pharmaceutical industry.

It is well-known that cell cycle arrest and/or death play a pivotal role in tumor progression, which has drawn a rising attention for cancer biologists due to their complex and intricate relationships. In this review, we demonstrate the recent research on oridonin, an active diterpenoid with remarkable antiproliferative activities, and then further explore its molecular mechanisms of cell cycle arrest, apoptosis, autophagy and their cross-talks in various cancer cells, which may provide a new perspective of oridonin as a candidate anti-neoplastic drug for future cancer therapeutics.

The Galanthus nivalis agglutinin (GNA)-related lectin family exhibit significant anti-HIV and anti-HSV properties that are closely related to their carbohydratebinding activities. However, there is still no conclusive evidence that GNA-related lectins possess anti-influenza properties. The hemagglutinin (HA) of influenza virus is a surface protein that is involved in binding host cell sialic acid during the early stages of infection. Herein, we studied the 3D-QSARs (three-dimensional quantitative structure-activity relationships) of lectin-and HA-sialic acid by molecular modeling. The affinities and stabilities of lectin-and HA-sialic acid complexes were also assessed by molecular docking and molecular dynamics simulations. Finally, anti-influenza GNA-related lectins that possess stable conformations and higher binding affinities for sialic acid than HAs of human influenza virus were screened, and a possible mechanism was proposed. Accordingly, our results indicate that some GNA-related lectins, such as Yucca filamentosa lectin and Polygonatum cyrtonema lectin, could act as drugs that prevent influenza virus infection via competitive binding. In conclusion, the GNArelated lectin family may be helpful in the design of novel candidate agents for preventing influenza A infection through the use of competitive combination against sialic acid specific viral infection.

Polygonatum odoratum lectin (POL), a novel mannose-binding lectin with anti-viral and apoptosisinducing activities, was isolated from rhizomes of Polygonatum odoratum (Mill.) Druce. POL was a homo-tetramer with molecular weight of 11953.623 Da per subunits as determined by gel filtration, SDS-PAGE and mass spectrometry. Based on its N-terminal 29-amino acid sequence the full-length cDNA sequence of POL was cloned. Subsequent phylogenetic analysis and molecular modeling revealed that POL belonged to the Galanthus nivalis agglutinin (GNA)-related lectin family, which acquired unique mannose-binding specificity. The hemagglutinating activities of POL were metal ion-independent, and were stable within certain range of pH and temperature alterations. Moreover, POL showed remarkable anti-HSV-II activity towards Vero cells, cytotoxicity towards human melanoma A375 cells and induced apoptosis in a caspase-dependent manner.

Polygonatum cyrtonema lectin (PCL), a mannose/sialic acid-binding lectin, has been reported to display remarkable anti-proliferative and apoptosis-inducing activities toward a variety of cancer cells; however, the precise molecular mechanisms by which PCL induces cancer cell death are still elusive. In the current study, we found that PCL could induce apoptosis and autophagy in murine fibrosarcoma L929 cells. Subsequently, we demonstrated that inhibition of Ras could promote L929 cell death, suggesting that RaseRaf signaling pathway plays the key negative regulator in PCL-induced apoptosis. And, we showed that Ras-Raf signaling pathway was also involved in PCL-induced autophagy as the negative regulator. In addition, we found that class I phosphatidylinositol 3-kinase (PI3K)eAkt signaling pathway could play the negative regulator in PCL-induced apoptosis and autophagy. Taken together, these results demonstrate that PCL induces murine fibrosarcoma L929 cell apoptosis and autophagy via blocking Ras-Raf and PI3KeAkt signaling pathways.

Plant lectins, carbohydrate-binding proteins distributed widely in a variety of plant species, have drawn a rising attention for cancer biologists due to their remarkable anti-tumour properties. In this review, we present a brief outline of the up-to-date advances of plant lectins in elucidating their complex anti-cancer mechanisms implicated in apoptosis and autophagy. In addition, we further discuss the pre-clinical and clinical studies of plant lectins for their potential therapeutic applications. In conclusion, these inspiring findings would open a new perspective for plant lectins as potential antineoplastic drugs from bench to clinic.

A 48 kDa, chitin-binding lectin with antifungal, antiviral and apoptosis-inducing activities was isolated from the rhizomes of Setcreasea purpurea Boom, a member of family Commelinaceae. Setcreasea purpurea lectin (designated as SPL) is a homotetrameric protein consisting of 12031.9 Da subunits linked by noncovalent bonds as determined by SDS-PAGE, gel filtration and MS. The N-terminal 25 amino-acid sequence of SPL, NVLGRDAYCGSQNPGATCPGLCCSK was determined and homology analysis suggested that SPL belongs to the family of chitin-binding plant lectins composed of hevein domains. The lectin exhibited strong hemagglutinating activity towards rabbit erythrocytes at 0.95 g/ml and the activity could be reversed exclusively by chitin hydrolysate (oligomers of GlcNAc). Its hemagglutinating activity was stable in pH range of 2.0-9.0 and it showed excellent thermal tolerance. SPL showed antifungal activity against Rhizoctonia solani, Sclerotinia sclerotiorum, Penicillium italicum and Helminthosporiun maydis. It also exhibited inhibitory effect on HIV-1 (IIIB) and HIV-2 (ROD), with an EC50 of 13.8±1.3 and 57.1±15 g/ml, respectively. Subsequently, MTT method, cell morphological analysis and LDH activity-based cytotoxicity assays demonstrated that SPL was highly cytotoxic to CNE-1 cells and induced apoptosis in a dosedependent manner. Moreover, due to the caspase inhibitors analyses, caspase was also found to play an important role in the potential apoptotic mechanism of SPL.

Galanthus nivalis agglutinin (GNA)-related lectin family, a superfamily of strictly mannose-binding specific lectins, has been well-known to possess several biological functions including apoptosis-inducing activities. However, the precise mechanisms of GNA-related lectins to induce apoptosis remains to be clarified. In this study, we showed that Polygonatum cyrtonema lectin (PCL) and Ophiopogon japonicus lectin (OJL), the two mannose-binding GNA-related lectins, could induce murine fibrosarcoma L929 cell apoptosis. In addition, we found that there was a close link between their sugar-binding and apoptosisinducing activities. Interestingly, we further confirmed that the mechanism of lectin-induced apoptosis was a caspase-dependent pathway. Moreover, we found that the two lectins could amplify tumor necrosis factorα (TNFα)-induced apoptosis. Taken together, these findings would open a new perspective for GNA-related lectins as potential anti-tumor agents.

Polygonatum cyrtonema lectin (PCL) is a novel anti-HIV mannose-binding lectin from Galanthus nivalis agglutinin (GNA)-related lectin family. Crystal structures of ligand-free PCL and its complexes with monomannoside and a1-3 dimannoside have been determined. The ligand-free PCL is dimeric, with both subunits adopt the b-prism II fold. PCL subunit binds mannose using a potential bivalent mode instead of the usual trivalent mode, in which carbohydrate-binding site (CBS) I and CBS III adopt the conserved mannose-binding motif of QXDXNXVXY (X is one of any amino acid residues) as observed in other structurally characterized GNA-related lectins, while CBS II adopts a modified motif with residues Gln58 and Asp60, which are critical for mannose-binding, substituted by His58 and Asn60, respectively. As a result, CBS II is unfit for mannose-binding. In the mannoside complexes, ligand-bindings only occur at CBS I which provides the specificity for a1-3 dimannoside. CBS II and CBS III are cooperatively occupied by a well-ordered sulfate ion, through which the individual dimers are cross-linked to form a unique superstructure of 32 helical lattice. Surveying the sequences of GNA-related lectins revealed that the modified binding motif of CBS II is widely distributed in the Liliaceae family as an intrinsic structural element. There is evidence that other GNA-related lectins will also adopt the similar super-structure as PCL. Thus PCL structure, unique in ligand-binding mode, may represent a novel type of structure of GNA-related lectins. Comparative analyses indicated that the dimer-based super-structure may play a primary role in the anti-HIV property of PCL.