Osteopontin knockdown inhibits αv,β3 integrin-induced cell migration and invasion and promotes apoptosis of breast cancer cells by inducing autophagy and inactivating the PI3K/Akt/mTOR pathway.
BACKGROUND
Osteopontin (OPN) is associated with tumor formation, progression and metastasis, and increased OPN levels have been associated with poor survival in breast cancer. We investigated the mechanisms responsible for OPN activity, and the relationships between OPN expression and clinical parameters in breast cancer.


METHODS
OPN mRNA and protein levels were compared in malignant and benign breast tumors by polymerase chain reaction (PCR) and immunohistochemistry, respectively, and levels in breast cancer cells were determined by PCR and western blotting. The effects of lentiviral-mediated knockdown of OPN on OPN and αv,β3 integrin expression, cell invasion and migration, autophagy and apoptosis were analyzed in MDA-MB-231 cells.


RESULTS
OPN expression increased with aggressiveness of breast cancer phenotype. OPN knockdown inhibited αv,β3 integrin expression in MDA-MB-231 cells, with subsequent inhibition of cell migration and invasion. Knockdown also inhibited the PI3K/Akt/mTOR pathway, promoted expression of the autophagy-related gene products LC3 and Beclin 1, and increased apoptosis. OPN expression was positively associated with tumor grade and lymph node metastasis.


CONCLUSIONS
These results suggest that knockdown of OPN may inhibit breast cancer metastasis by regulating αv,β3 integrin expression and inducing autophagy and subsequent inhibition of PI3K/Akt/mTOR signaling, thus providing further insights into the complex mechanisms regulating tumor growth and metastasis.
Department of Breast Surgery, Central Hospital of Nanyang City, Nanyang, China.
Hao
H
Zhang
Man
M
Guo
Jin-Hong
JH
Chen
Zheng
Z
Wang
Xin-Feng
XF
Du
Ping-Xian
PX
Liu
Wei-Han
WH
Li
D000328:Adult; D000368:Aged; D017209:Apoptosis; D001343:Autophagy; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D002465:Cell Movement; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D061986:MCF-7 Cells; D008875:Middle Aged; D053495:Osteopontin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
D039302:Integrin alphaVbeta3; D053495:Osteopontin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human