Regulation of mTOR Signaling by Semaphorin 3F-Neuropilin 2 Interactions In Vitro and In Vivo

Abstract

Semaphorin 3F (SEMA3F) provides neuronal guidance cues via its ability to bind neuropilin 2 (NRP2) and Plexin A family molecules. Recent studies indicate that SEMA3F has biological effects in other cell types, however its mechanism(s) of function is poorly understood. Here, we analyze SEMA3F-NRP2 signaling responses in human endothelial, T cell and tumor cells using phosphokinase arrays, immunoprecipitation and Western blot analyses. Consistently, SEMA3F inhibits PI-3K and Akt activity, and responses are associated with the disruption of mTOR/rictor assembly and mTOR-dependent activation of the RhoA GTPase. We also find that the expression of vascular endothelial growth factor, as well as mTOR-inducible cellular activation responses and cytoskeleton stability are inhibited by SEMA3F-NRP2 interactions in vitro. In vivo, local and systemic overproduction of SEMA3F reduces tumor growth in NRP2-expressing xenografts. Taken together, SEMA3F regulates mTOR signaling in diverse human cell types, suggesting that it has broad therapeutic implications.

The intragraft microenvironment as a central determinant of chronic rejection or local immunoregulation/tolerance

“…More recent studies have demonstrated that this family, including SEMA3 family members, regulate a wider array of cellular activation responses, most notably PI-3K/Akt/mTOR intracellular signaling, migration and proliferation [81–83]. Over the past 10 years, several studies have identified SEMA3 receptors, including neuropilin (NRP)-1, NRP-2 and Plexin A family molecules on tumor cells suggesting that they function within the tumor microenvironment to limit cellular migration and growth [80,81,84,85]. Three members of the Class 3 family (SEMA3A, -3C and -3F) also bind NRP’s that are expressed on immune cell types including EC [75–78,81], antigen presenting cells [86,87] and CD4 + T cells [70].…”

“…Over the past 10 years, several studies have identified SEMA3 receptors, including neuropilin (NRP)-1, NRP-2 and Plexin A family molecules on tumor cells suggesting that they function within the tumor microenvironment to limit cellular migration and growth [80,81,84,85]. Three members of the Class 3 family (SEMA3A, -3C and -3F) also bind NRP’s that are expressed on immune cell types including EC [75–78,81], antigen presenting cells [86,87] and CD4 + T cells [70]. In general, ligation of the NRP receptor alone is not sufficient to elicit a signal, but serves as co-receptor to activate Plexin A family receptors that in turn elicit potent inhibitory signaling responses [88,89].…”

“…Indeed, deletion of Plexin A on CD4+ cells is associated with profound effector T cell activation and autoimmunity [88] Both NRPs also bind additional molecules including VEGF, Placental Growth Factor and Sema4A and thus may serve to augment binding/crosslinking of their classical receptors. In this manner, these molecules may compete with SEMA3’s for their NRP binding domain and regulate SEMA-NRP-elicited inhibitory signaling responses [81,90]. As will be discussed below, two members, namely SEMA3A and SEMA3F have high potential to interact with NRP-1 and NRP-2, respectively, on T cells and EC; thus, it is not surprising that they have potential to inhibit T cell activation and migration and to serve as regulators of the immune responses.…”

The role of the semaphorins in cancer

“…These, and responses were associated with the disruption of mTOR/rictor assembly and mTOR-dependent activation of the RhoA GTPase. 202 In addition, sema3F also has effects on the tumor microenvironment which contribute to its tumor progression inhibiting ability. It functions as a potent inhibitor of tumor angiogenesis 102,103 and as a result can inhibit tumor progression even when the tumor cells themselves do not express sema3F receptors.…”

Inflammation and Lymphedema Are Exacerbated and Prolonged by Neuropilin 2 Deficiency

“…SEMA3F protein has been shown to compete with VEGFA on NRP2 35 and to inhibit EC functions. 33,40,41 Loss of the functional Sema3F receptor, Nrp2, increased edema and lymphedema after inflammation. This conclusion is based on findings from previous structural studies that have suggested that VEGFA binds between NRP receptor and VEGFR2 in a bridge formation.…”