Abstract
Ribosome inactivating proteins (RIPs) are highly potent cytotoxins that have potential as anticancer therapeutics. Mistletoe lectin 1 (ML1) is a heterodimeric cytotoxic protein isolated from European Mistletoe and belongs to RIP class II. The aim of this project was to systematically study ML1 cell binding, endocytosis pathway(s), subcellular processing and apoptosis activation. For this purpose, state of the art cell imaging equipment and automated image analysis algorithms were used. ML1 displayed very fast binding to sugar residues on the membrane and energy-dependent uptake in CT26 cells. The co-staining with specific antibodies and uptake blocking experiments revealed involvement of both clathrin-dependent and -independent pathways in ML1 endocytosis. Co-localization studies demonstrated the toxin transport from early endocytic vesicles to Golgi network; a retrograde road to the endoplasmic reticulum. The pro-apoptotic and antiproliferative activity of ML1 were shown in time lapse movies and subsequently quantified. ML1 cytotoxicity was less affected in multidrug resistant tumor cell line 4T1 in contrast to commonly used chemotherapeutic drug (ML1 resistance index 6.9 vs 13.4 for doxorubicin; IC50: ML1 1.4 ng/ml vs doxorubicin 24000 ng/ml). This opens new opportunities for the use of ML1 as an alternative treatment in multidrug resistant cancers.
Highlights
Ribosome inactivating proteins (RIPs) are highly potent cytotoxins that interfere in protein biosynthesis
The class of heterodimeric ~60 kDa RIP-II cytotoxins has the enzymatic chain linked to a lectin chain, often referred as B-chain
We investigated in detail Mistletoe lectin 1 (ML1) binding, uptake pathways and endosomal escape mechanisms in correlation with its cytotoxic activity in living cells
Summary
Ribosome inactivating proteins (RIPs) are highly potent cytotoxins that interfere in protein biosynthesis. The class of heterodimeric ~60 kDa RIP-II cytotoxins has the enzymatic chain linked to a lectin chain, often referred as B-chain. Specific cell binding ligands could be conjugated to RIP-I to increase the therapeutic value. In addition to these two classes, RIP type III cytotoxins consist of a toxic unit linked to a peptide with unknown function[10]. Mistletoe lectin 1 (ML1) is categorized as RIP-II and it is one of the main active components of Viscum album extracts. European ML1 shares 84% homology with Korean ML14–19, it cannot be assumed they have the same subcellular modes of action and pathways; the same is true for recombinant variations of mistletoe lectin or plant extracts containing ML120–23
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
