Down-regulation of some miRNAs by degrading their precursors contributes to anti-cancer effect of mistletoe lectin-I.
OBJECTIVE
Mistletoe lectin-I (ML-I), the main anti-cancer component of mistletoe extracts, was originally thought to act exclusively on 28S rRNA. Here, we investigate the down-regulating effect and mechanism of CM-1, an ML-I isolated from Chinese mistletoe, on some miRNAs.


METHODS
The anti-cancer effects of CM-1 were assessed in vitro and in vivo in colorectal cancer cells. The miRNAs down-regulated by CM-1 were identified by miRNA microarray assay and validated by qRT-PCR analysis. The suppression of host gene transcription or by degradation of precursors was determined by qRT-PCR and enzyme activity assays respectively. The qRT-PCR, Western blot and immunohistochemistry were used to examine the expression of their target gene and related downstream effector. Cell proliferation was assayed in stably transfected HEK-293 cells with different levels of these miRNAs.


RESULTS
CM-1 showed prominent anti-neoplastic activity towards CLY and HT-29 cells both in vitro and in vivo. The miR-135a&b were the miRNAs most down-regulated by CM-1. Their host gene transcription was largely up-regulated, while their precursors were degraded directly by CM-1. The expression of their target gene adenomatous polyposis coli and the phosphorylation of related effector β-catenin were both significantly up-regulated. The IC(50) values of CM-1 on derivative HEK-293 cells with high miR-135a&b levels were 2-4 times lower than that of control cells.


CONCLUSIONS
CM-1 down-regulated some miRNAs by degrading their precursors, which contributes to its prominent anti-cancer activity.
Department of Pharmacology and Toxicology, Beijing Institute of Radiation Medicine, China. linnali365@yahoo.cn
Lin-Na
LN
Li
Hua-Dong
HD
Zhang
Run
R
Zhi
Shou-Jun
SJ
Yuan
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology / Q000627:therapeutic use*; D015536:Down-Regulation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D057809:HEK293 Cells; D019073:HT29 Cells; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D058990:Molecular Targeted Therapy; D009374:Neoplasms, Experimental / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D008517:Phytotherapy; D018515:Plant Leaves / Q000737:chemistry; D040081:Protein Array Analysis; D012322:RNA Precursors / Q000378:metabolism*; D054790:Ribosome Inactivating Proteins, Type 2 / Q000494:pharmacology / Q000627:therapeutic use*; D014118:Toxins, Biological / Q000494:pharmacology / Q000627:therapeutic use*; D028181:Viscum / Q000737:chemistry
D000972:Antineoplastic Agents, Phytogenic; C544965:MIRN135 microRNA, human; D035683:MicroRNAs; D012322:RNA Precursors; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; C488862:mistletoe lectin I