Deciphering downstream gene targets of PI3K/mTOR/p70S6K pathway in breast cancer.
BACKGROUND
The 70 kDa ribosomal protein S6 kinase (RPS6KB1), located at 17q23, is amplified and overexpressed in 10-30% of primary breast cancers and breast cancer cell lines. p70S6K is a serine/threonine kinase regulated by PI3K/mTOR pathway, which plays a crucial role in control of cell cycle, growth and survival. Our aim was to determine p70S6K and PI3K/mTOR/p70S6K pathway dependent gene expression profiles by microarrays using five breast cancer cell lines with predefined gene copy number and gene expression alterations. The p70S6K dependent profiles were determined by siRNA silencing of RPS6KB1 in two breast cancer cell lines overexpressing p70S6K. These profiles were further correlated with gene expression alterations caused by inhibition of PI3K/mTOR pathway with PI3K inhibitor Ly294002 or mTOR inhibitor rapamycin.


RESULTS
Altogether, the silencing of p70S6K altered the expression of 109 and 173 genes in two breast cancer cell lines and 67 genes were altered in both cell lines in addition to RPS6KB1. Furthermore, 17 genes including VTCN1 and CDKN2B showed overlap with genes differentially expressed after PI3K or mTOR inhibition. The gene expression signatures responsive to both PI3K/mTOR pathway and p70S6K inhibitions revealed previously unidentified genes suggesting novel downstream targets for PI3K/mTOR/p70S6K pathway.


CONCLUSIONS
Since p70S6K overexpression is associated with aggressive disease and poor prognosis of breast cancer patients, the potential downstream targets of p70S6K and the whole PI3K/mTOR/p70S6K pathway identified in our study may have diagnostic value.
Heinonen
Henna
H
Institute of Biomedicine and Biomedicum Biochip Center, Genome-Scale Biology Research Program, University of Helsinki, Finland. henna.heinonen@helsinki.fi
Nieminen
Anni
A
Saarela
Matti
M
Kallioniemi
Anne
A
Klefström
Juha
J
Hautaniemi
Sampsa
S
Monni
Outi
O
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000235:genetics*; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D020411:Oligonucleotide Array Sequence Analysis; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011494:Protein Kinases / Q000187:drug effects / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000187:drug effects / Q000235:genetics*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
D000903:Antibiotics, Antineoplastic; D002867:Chromones; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011494:Protein Kinases; D034741:RNA, Small Interfering; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1