miR-200 enhances mouse breast cancer cell colonization to form distant metastases.
BACKGROUND
The development of metastases involves the dissociation of cells from the primary tumor to penetrate the basement membrane, invade and then exit the vasculature to seed, and colonize distant tissues. The last step, establishment of macroscopic tumors at distant sites, is the least well understood. Four isogenic mouse breast cancer cell lines (67NR, 168FARN, 4TO7, and 4T1) that differ in their ability to metastasize when implanted into the mammary fat pad are used to model the steps of metastasis. Only 4T1 forms macroscopic lung and liver metastases. Because some miRNAs are dysregulated in cancer and affect cellular transformation, tumor formation, and metastasis, we examined whether changes in miRNA expression might explain the differences in metastasis of these cells.


RESULTS
miRNA expression was analyzed by miRNA microarray and quantitative RT-PCR in isogenic mouse breast cancer cells with distinct metastatic capabilities. 4T1 cells that form macroscopic metastases had elevated expression of miR-200 family miRNAs compared to related cells that invade distant tissues, but are unable to colonize. Moreover, over-expressing miR-200 in 4TO7 cells enabled them to metastasize to lung and liver. These findings are surprising since the miR-200 family was previously shown to promote epithelial characteristics by inhibiting the transcriptional repressor Zeb2 and thereby enhancing E-cadherin expression. We confirmed these findings in these cells. The most metastatic 4T1 cells acquired epithelial properties (high expression of E-cadherin and cytokeratin-18) compared to the less metastatic cells.


CONCLUSIONS
Expression of miR-200, which promotes a mesenchymal to epithelial cell transition (MET) by inhibiting Zeb2 expression, unexpectedly enhances macroscopic metastases in mouse breast cancer cell lines. These results suggest that for some tumors, tumor colonization at metastatic sites might be enhanced by MET. Therefore the epithelial nature of a tumor does not predict metastatic outcome.
Department of Pediatrics, Immune Disease Institute, Harvard Medical School, Boston, Massachusetts, United States of America. ddykxhoorn@med.miami.edu
Derek M
DM
Dykxhoorn
Yichao
Y
Wu
Huangming
H
Xie
Fengyan
F
Yu
Ashish
A
Lal
Fabio
F
Petrocca
Denis
D
Martinvalet
Erwei
E
Song
Bing
B
Lim
Judy
J
Lieberman
D020413:3' Untranslated Regions; D000818:Animals; D015820:Cadherins / Q000096:biosynthesis; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D003001:Cloning, Molecular; D004848:Epithelium / Q000378:metabolism; D005260:Female; D018398:Homeodomain Proteins / Q000378:metabolism; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism; D015674:Mammary Neoplasms, Animal / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D035683:MicroRNAs / Q000378:metabolism*; D008856:Microscopy, Fluorescence / Q000379:methods; D009362:Neoplasm Metastasis; D016896:Treatment Outcome; D000071799:Zinc Finger E-box-Binding Homeobox 1
D020413:3' Untranslated Regions; D015820:Cadherins; D018398:Homeodomain Proteins; D051741:Kruppel-Like Transcription Factors; D035683:MicroRNAs; C543719:Mirn200 microRNA, mouse; C519422:ZEB1 protein, mouse; D000071799:Zinc Finger E-box-Binding Homeobox 1