[Blockage of mTOR signaling pathway by rapamycin contributes to inhibition of tumor cell proliferation in ALK-positive lymphoid cell strains].

ABSTRACT

OBJECTIVE: To investigate the relationship between mTOR signaling pathway and ALK-positive lymphoid cell lines. METHODS: The expression of the downstream effector proteins of mTOR were analyzed by Western blot before and after Karpas299, BaF3/NPM-ALK and BaF3 cell lines treated with rapamycin. Effect of rapamycin on cell proliferation was detected by MTT assay. FACS was used to analyze apoptosis and cell cycles. RESULTS: mTOR signaling phosphoproteins, p-p70S6K and p-4E-BP1 were highly expressed in ALK(+) Karpas299, BaF3/NPM-ALK and parental BaF3 cell lines, and they were dephosphorylated after 1 h withdrawal of IL-3 in BaF3 cells. After 48 h exposure to 10 nmol/L rapamycin, p-p70S6K and p-4E-BP1 proteins expression were decreased, and mainly for the former. The relative inhibitory rate to its control cells was 24.4% in Karpas299, 37.8% in BaF3/NPM-ALK and 61.6% in BaF3. The apoptotic ratio was increased from (11.97 +/- 0.11)% to (15.87 +/- 0.62)% in Karpas299 (P < 0.05), from (3.23 +/- 0.11)% to (7.67 +/- 0.49)% in BaF3 (P < 0.05) and from (1.90 +/- 0.47)% to (2.80 +/- 0.27)% in BaF3/NPM-ALK (P > 0.05). The fraction of G(1) phase cells increased from (37.63 +/- 1.91)% to (69.77 +/- 5.44)% in BaF3/NPM-ALK, from (31.13 +/- 2.51)% to (40.70 +/- 1.47)% in Karpas299 and (53.57 +/- 2.22)% to (63.70 +/- 1.20)% in BaF3 (P < 0.05). CONCLUSION: NPM-ALK kinase can activate mTOR signaling pathway. Rapamycin can inhibit the proliferation of ALK(+) lymphoid cells by blocking mTOR signaling pathway and inducing cell cycling arrest at G(1) phase.