BACKGROUND: MicroRNA-101 (miR-101) expression is negatively associated with 
tumor growth and blood vessel formation in several solid epithelial cancers. 
However, the role of miR-101 in human breast cancer remains elusive.
RESULTS: MiR-101 was significantly decreased in different subtypes of human 
breast cancer tissues compared with that in adjacent normal breast tissues 
(P<0.01). Up-regulation of miR-101 inhibited cell proliferation, migration and 
invasion, and promoted cell apoptosis in ER alpha-positive and ER alpha-negative 
breast cancer cells and normal breast cells. Down-regulation of miR-101 
displayed opposite effects on cell growth and metastasis. Further investigation 
revealed a significant inverse correlation between the expression of miR-101 and 
Stathmin1 (Stmn1), and miR-101 could bind to the 3'-untranslated region (UTR) of 
Stmn1 to inhibit Stmn1 translation. The inhibition of cell growth and metastasis 
induced by up-regulation of miR-101 was partially restored by overexpression of 
Stmn1. Knockdown of Stmn1 attenuates the down-regulation of miR-101-mediated 
enhancement of cell growth and metastasis. More importantly, in vivo analysis 
found that Stmn1 mRNA and protein level in different subtypes of human breast 
cancer tissues, contrary to the down-regulation of miR-101, were significantly 
elevated.
CONCLUSIONS: This study demonstrates that down-regulation of miR-101 in 
different subtypes of human breast cancer tissues is linked to the increase of 
cellular proliferation and invasiveness via targeting Stmn1, which highlights 
novel regulatory mechanism in breast cancer and may provide valuable clues for 
the future clinical diagnosis of breast cancer.