Activation of Mammalian Target of Rapamycin Signaling Pathway Contributes to Tumor Cell Survival in Anaplastic Lymphoma Kinase–Positive Anaplastic Large Cell Lymphoma

Abstract

Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) frequently carries the t(2;5)(p23;q35) resulting in aberrant expression of chimeric nucleophosmin-ALK. Previously, nucleophosmin-ALK has been shown to activate phosphatidylinositol 3-kinase (PI3K) and its downstream effector, the serine/threonine kinase AKT. In this study, we hypothesized that the mammalian target of rapamycin (mTOR) pathway, which functions downstream of AKT, mediates the oncogenic effects of activated PI3K/AKT in ALK+ ALCL. Here, we provide evidence that mTOR signaling phosphoproteins, including mTOR, eukaryotic initiation factor 4E-binding protein-1, p70S6K, and ribosomal protein S6, are highly phosphorylated in ALK+ ALCL cell lines and tumors. We also show that AKT activation contributes to mTOR phosphorylation, at least in part, as forced expression of constitutively active AKT by myristoylated AKT adenovirus results in increased phosphorylation of mTOR and its downstream effectors. Conversely, inhibition of AKT expression or activity results in decreased mTOR phosphorylation. In addition, pharmacologic inhibition of PI3K/AKT down-regulates the activation of the mTOR signaling pathway. We also show that inhibition of mTOR with rapamycin, as well as silencing mTOR gene product expression using mTOR-specific small interfering RNA, decreased phosphorylation of mTOR signaling proteins and induced cell cycle arrest and apoptosis in ALK+ ALCL cells. Cell cycle arrest was associated with modulation of G 1 -Sphase regulators, including the cyclin-dependent kinase inhibitors p21 waf1 and p27 kip1 . Apoptosis following inhibition of mTOR expression or function was associated with downregulation of antiapoptotic proteins, including c-FLIP, MCL-1, and BCL-2. These findings suggest that the mTOR pathway contributes to nucleophosmin-ALK/PI3K/AKTmediated tumorigenesis and that inhibition of mTOR represents a potential therapeutic strategy in ALK+ ALCL.

18F-FDG PET in Patients with Primary Systemic Anaplastic Large Cell Lymphoma: Differential Features According to Expression of Anaplastic Lymphoma Kinase

“…Many primary systemic ALK-positive ALCLs express the NPM-ALK fusion protein, and this protein can elicit multiple signaling pathways, which are responsible for both cell transformation and maintenance of the neoplastic phenotype [19]. Of these signaling pathways, the Ras-extracellular signal-regulated kinase (ERK) pathway primarily takes charge of translating the downstream effectors, mTOR and its target proteins for ALCL proliferation [20][21][22]. The phosphatidylinositol 3-kinase (PI3K)-Akt pathway also accounts for the small role for the ALCL proliferation [22].…”

Oncogenic tyrosine kinase NPM/ALK induces activation of the rapamycin-sensitive mTOR signaling pathway

“…As we have found, the MEK/ERK pathway activates mTOR in ALK þ TCL cells and it does so more strongly than PI3K/Akt. A recent study (Vega et al, 2006) identified mTOR activation in ALK þ TCL and implicated Akt in the process. Our findings not only demonstrate that mTOR activation is triggered by NPM/ALK and that nutrients are required as the second signal for the mTOR activation in the ALK þ TCL cells but also, as discussed above, indicate that the contribution of PI3K/Akt to mTOR activation is relatively limited in such cells, in particular when compared with the MEK/ERK pathway.…”

N-terminal PAX8 polyclonal antibody shows cross-reactivity with N-terminal region of PAX5 and is responsible for reports of PAX8 positivity in malignant lymphomas

“…16 Briefly, tissue sections were subjected to deparafinization, hydration and heat-induced epitope retrieval in pH 6.0 citrate buffer (Dako, Carpinteria, CA, USA) in a steam humidifier for 30 min, followed by gradual cooling for 20 min. Endogenous peroxidase reaction was blocked by 3% H 2 O 2 solution for 10 min.…”