Inhibition of Chemokine (CXC Motif) Ligand 12/Chemokine (CXC Motif) Receptor 4 Axis (CXCL12/CXCR4)-mediated Cell Migration by Targeting Mammalian Target of Rapamycin (mTOR) Pathway in Human Gastric Carcinoma Cells

Abstract

CXCL12/CXCR4 plays an important role in metastasis of gastric carcinoma. Rapamycin has been reported to inhibit migration of gastric cancer cells. However, the role of mTOR pathway in CXCL12/CXCR4-mediated cell migration and the potential of drugs targeting PI3K/mTOR pathway remains unelucidated. We found that CXCL12 activated PI3K/Akt/mTOR pathway in MKN-45 cells. Stimulating CHO-K1 cells expressing pEGFP-C1-Grp1-PH fusion protein with CXCL12 resulted in generation of phosphatidylinositol (3,4,5)-triphosphate, which provided direct evidence of activating PI3K by CXCL12. Down-regulation of p110β by siRNA but not p110α blocked phosphorylation of Akt and S6K1 induced by CXCL12. Consistently, p110β-specific inhibitor blocked the CXCL12-activated PI3K/Akt/mTOR pathway. Moreover, CXCR4 immunoprecipitated by anti-p110β antibody increased after CXCL12 stimulation and Gi protein inhibitor pertussis toxin abrogated CXCL12-induced activation of PI3K. Further studies demonstrated that inhibitors targeting the PI3K/mTOR pathway significantly blocked the chemotactic responses of MKN-45 cells triggered by CXCL12, which might be attributed primarily to inhibition of mTORC1 and related to prevention of F-actin reorganization as well as down-regulation of active RhoA, Rac1, and Cdc42. Furthermore, rapamycin inhibited the secretion of CXCL12 and the expression of CXCR4, which might form a positive feedback loop to further abolish upstream signaling leading to cell migration. Finally, we found cells expressing high levels of cxcl12 were sensitive to rapamycin in its activity inhibiting migration as well as proliferation. In summary, we found that the mTOR pathway played an important role in CXCL12/CXCR4-mediated cell migration and proposed that drugs targeting the mTOR pathway may be used for the therapy of metastatic gastric cancer expressing high levels of cxcl12.

mTORC2 mediates CXCL12-induced angiogenesis

“…In addition, pretreatment with pertussis toxin, a G i protein inhibitor, abolished the activation of Akt at S473 induced by CXCL12. This is in line with reports in T lymphocytes and gastric cancer cells showing that G i protein is required for CXCL12-induced activation of PI3K and Akt at S473 [12,38]. Taken together these findings provide mechanistic insight into how CXCL12/CXCR4 signals to mTORC2 in EC (Fig.…”

“…To date there has been a paucity of information on the molecular mechanism of CXCL12/CXCR4 signal transduction in EC as most studies have focused on signal transduction in tumor cells [12,13,6]. mTORC2 is emerging as a central player in the promotion of cell migration via chemotactic receptors [27–29,16], however, the molecular connections linking receptors to mTORC2 activation is poorly understood.…”

“…This is important for vascular and cancer biology as we show that to significantly block angiogenesis mTORC2 signaling must be abrogated. This signaling cascade seems to be unique to the EC as tumor cells stimulated with CXCL12 activate both mTOR complexes [12,13,51]. Indeed, recent evidence also shows that EC rely more heavily on the mTORC2 signaling node for VEGF-mediated angiogenesis when compared with mTORC1 [52].…”

“…For example, CXCL12 activates mTOR in human gastric cancer cells and the targeting of mTOR inhibits CXCR4-mediated cell migration [12,13]. In EC, the CXCL12/CXCR4 signaling axis stimulates cell migration and angiogenesis through G-protein-mediated activation of Rac [14].…”

Alpha-fetoprotein activates AKT/mTOR signaling to promote CXCR4 expression and migration of hepatoma cells

“…Moreover, Dubrovska et al[30] demonstrated the direct regulation of CXCR4 expression by the PI3K pathway and thus implied a mutually positive regulatory feedback loop between the PI3K/AKT and CXCR4/CXCL12 signaling pathways, which are both important for cancer metastasis. Furthermore, our previous results indicated that HBV-X protein induced the expression of AFP in human normal liver cells, which correlated to CXCR4 expression in human hepatoma cells[31], and accumulated evidences showed that the mTOR/CXCR4 signal axis is closely associated with the promotion of cancer cell metastasis[32]. In the present study, we also explored the possible mechanisms by which AFP can regulate CXCR4 expression via knockdown of AFP in PLC/PRF/5 cells or appearance of AFP in pcDNA3.1- afp vectors transfected HLE cells.…”