mTORC2 activity is elevated in gliomas and promotes growth and cell motility via overexpression of rictor.
mTORC2 is a multimeric kinase composed of the mammalian target of rapamycin kinase (mTOR), mLST8, mSin1, and rictor. The complex is insensitive to acute rapamycin exposure and has shown functions in controlling cell growth and actin cytoskeletal assembly. mTORC2 has recently been shown to phosphorylate and activate Akt. Because approximately 70% of gliomas harbor high levels of activated Akt, we investigated whether mTORC2 activity was elevated in gliomas. In this study, we found that mTORC2 activity was elevated in glioma cell lines as well as in primary tumor cells as compared with normal brain tissue (P < 0.05). Moreover, we found that rictor protein and mRNA levels were also elevated and correlated with increased mTORC2 activity. Overexpression of rictor in cell lines led to increased mTORC2 assembly and activity. These lines exhibited increased anchorage-independent growth in soft agar, increased S-phase cell cycle distribution, increased motility, and elevated integrin beta(1) and beta(3) expression. In contrast, small interfering RNA-mediated knockdown of rictor inhibited these oncogenic activities. Protein kinase C alpha (PKC alpha) activity was shown to be elevated in rictor-overexpressing lines but reduced in rictor-knockdown clones, consistent with the known regulation of actin organization by mTORC2 via PKC alpha. Xenograft studies using these cell lines also supported a role for increased mTORC2 activity in tumorigenesis and enhanced tumor growth. In summary, these data suggest that mTORC2 is hyperactivated in gliomas and functions in promoting tumor cell proliferation and invasive potential due to increased complex formation as a result of the overexpression of rictor.
Masri
Janine
J
Department of Research and Development, Greater Los Angeles Veterans Affairs Healthcare System, Sepulveda, California 91343-2099, USA.
Bernath
Andrew
A
Martin
Jheralyn
J
Jo
Oak D
OD
Vartanian
Raffi
R
Funk
Alexander
A
Gera
Joseph
J
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D001932:Brain Neoplasms; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002453:Cell Cycle; D002455:Cell Division; D045744:Cell Line, Tumor; D002465:Cell Movement; D003114:Colony-Forming Units Assay; D015972:Gene Expression Regulation, Neoplastic; D005910:Glioma / Q000235:genetics* / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D016086:Lentivirus / Q000235:genetics; D009361:Neoplasm Invasiveness; D010957:Plasmids; D011401:Promoter Regions, Genetic; D051571:Protein Kinase C-alpha / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C493277:MAPKAP1 protein, human; C492571:RICTOR protein, human; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D014157:Transcription Factors; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D051571:Protein Kinase C-alpha