| First Author | Zhang H | Year | 2003 |
| Journal | J Clin Invest | Volume | 112 |
| Issue | 8 | Pages | 1223-33 |
| PubMed ID | 14561707 | Mgi Jnum | J:162300 |
| Mgi Id | MGI:4818565 | Doi | 10.1172/JCI17222 |
| Citation | Zhang H, et al. (2003) Loss of Tsc1/Tsc2 activates mTOR and disrupts PI3K-Akt signaling through downregulation of PDGFR. J Clin Invest 112(8):1223-33 |
| abstractText | Tuberous sclerosis (TSC) is a familial tumor syndrome due to mutations in TSC1 or TSC2, in which progression to malignancy is rare. Primary Tsc2(-/-) murine embryo fibroblast cultures display early senescence with overexpression of p21CIP1/WAF1 that is rescued by loss of TP53. Tsc2(-/-)TP53(-/-) cells, as well as tumors from Tsc2(+/-) mice, display an mTOR-activation signature with constitutive activation of S6K, which is reverted by treatment with rapamycin. Rapamycin also reverts a growth advantage of Tsc2(-/-)TP53(-/-) cells. Tsc1/Tsc2 does not bind directly to mTOR, however, nor does it directly influence mTOR kinase activity or cellular phosphatase activity. There is a marked reduction in Akt activation in Tsc2(-/-)TP53(-/-) and Tsc1(-/-) cells in response to serum and PDGF, along with a reduction in cell ruffling. PDGFRalpha and PDGFRbeta expression is markedly reduced in both the cell lines and Tsc mouse renal cystadenomas, and ectopic expression of PDGFRbeta in Tsc2-null cells restores Akt phosphorylation in response to serum, PDGF, EGF, and insulin. This activation of mTOR along with downregulation of PDGFR PI3K-Akt signaling in cells lacking Tsc1 or Tsc2 may explain why these genes are rarely involved in human cancer. This is in contrast to PTEN, which is a negative upstream regulator of this pathway. |
