Abstract B26: PI3K class I and mTOR regulate distinct steps in Met dependent tumorigenesis
Authors: Hervieu Alexia , Kermorgant Stephanie 
Published: October 2015

The Receptor Tyrosine Kinase (RTK) Met, overexpressed or mutated in cancer, plays a major role in cancer progression and represents an attractive target for cancer therapy. Although several Met inhibitors are in clinical trials, resistance may occur as experienced in the clinic with other RTKs. Thus, a need for alternative / complementary therapy may be required to target Met driven tumors efficiently.

The aim of this study was to investigate whether PI3K plays a role in Met oncogenic activity, in view of designing appropriate therapy.

The study was performed on two cell models suitable to study Met driven NIH3T3 cells expressing Met Wt or the constitutively active mutant M1268T and the glioblastoma U87MG cell line, with Met constitutively activated due to an autocrine loop. Transwell cell migration and anchorage independent growth in soft agar were studied in presence of inhibitors targeting pan-PI3K (LY294002 and wortmannin), isoform-specific PI3K (GDC0941, pan-PI3K class I, A66, p110 alpha, TGX221, p110 beta) and mTOR (rapamycin), or following siRNA knock down of PI3K isoforms. Tumor growth of cells grafted to nude mice was assessed in presence or absence of rapamycin.

LY294002 reduced the migration and the anchorage independent growth of Met mutant M1268T expressing cells to the same level as with Met Wt expressing cells, while no difference was detected in Met Wt expressing cells.

Inhibitions / knock downs of PI3K class I reduced the migration of Met M1268T expressing cells and UMG87 cells. Interestingly, it was determined that p110 alpha and beta together are responsible for Met dependent cell migration. Moreover, the phosphorylation (Ser473) of Akt, the downstream effector of PI3K class I, was significantly increased in Met M1268T versus Wt Met expressing cells. It was inhibited by Met pharmacological inhibition, indicating that Met M1268T activates Akt in these cells. Moreover, the inhibition of Met M1268T internalization using the dynamin inhibitor dynasore led to a significant reduction of Akt phosphorylation in these cells, suggesting further that Met M1268T activates Akt on endosome. Interestingly, the endosomal activation of Akt seems to be Appl1 independent.

Surprisingly, inhibitions / knock downs of PI3K class I did not decrease the anchorage independent growth of Met M1268T expressing cells and of U87MG cells. Wortmannin also had no effect. However, our results using the mTOR inhibitor indicate that in fact, mTOR is responsible for Met dependent anchorage independent growth in Met M1268T expressing cells and U87MG cells. Moreover, rapamycin significantly reduced Met dependent tumor growth in vivo.

Our results suggest that while PI3K class I (p110 alpha and beta) regulate oncogenic Met dependent cell migration, the anchorage independent growth and tumor growth are regulated by mTOR. These results may have implication for therapeutical intervention.

Citation Format: Alexia Hervieu, Stephanie Kermorgant. PI3K class I and mTOR regulate distinct steps in Met dependent tumorigenesis. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B26.