An interspecies conserved motif of the mouse immune system-released activating agent (ISRAA) induces proliferative effects on human cells

Abstract

We have recently described an immune system-released activating agent (ISRAA) as a nervous system-induced factor that stimulates immune responses in the mouse spleen. However, the human ISRAA has not yet been identified. In this study, we examined the effects of the mouse ISRAA protein on human peripheral blood mononuclear cells (PBMCs), to observe if the biological activity of this molecule is consistent between the two different species. Mouse ISRAA demonstrated dose-dependent dualistic effects on human cells, as 5 μg exhibited positive apoptosis and 50 pg exhibited significant proliferation (P<0.05). Furthermore, immunosuppressed cells from patients undergoing immunosuppressive therapy demonstrated significant proliferation to 50 pg ISRAA (P<0.05). Studies to compare sequences in different species revealed a preserved motif, exhibiting 72% similarity with the interspecies conserved signal peptide motif of tumor necrosis factor receptor 1 (TNFR1). A mutant ISRAA lacking this motif was produced and tested for its biological effects. The mutant ISRAA demonstrated neither apoptotic nor proliferative effects compared with wild type. Therefore, an interspecies conserved domain of ISRAA constitutes the active site of the molecule, and its effects on immunocompromised cells should be investigated for future therapies in the treatment of immunosuppressive disorders.

Induction of dissociated cytokine profiles by ISRAA with selective critical involvement of ERK1/2 in its signaling functions

“…The human counterpart of mouse ISRAA is not known; however, we recently demonstrated that ISRAA contains an interspecies-conserved functional motif sharing 72% homology with a motif present in the TNF receptor 1 (TNFR1), a receptor connected to intracellular domains inducing dose-dependent signals for survival or death, and the potential proliferative effects of mouse ISRAA on human cells were recorded (2). In this study, we reconfirmed this activity using different techniques and examined the induction of a broad spectrum of pro-inflammatory and anti-inflammatory cytokines in response to the stimulation of hPBMCs with ISRAA.…”

“…The effects of ISRAA on cells have been shown to be dualistic, as high concentrations induce apoptosis and low concentrations induce proliferation (2). This study demonstrated that ERK1/2 had no effect on the ISRAA-induced cell proliferation, while it was shown that ERK1/2 is required for ISRAA-induced apoptosis since the inhibition of ERK activities by a small molecule inhibitor almost completely inhibited the apoptotic effects of the high dose of ISRAA and reversed the suppressive effect of the cytotoxic dose.…”

“…ISRAA was initially considered to have a cytokine-like activity due to several factors, including its relatively low molecular mass, its biological effects on a broad spectrum of cell types, such as T and B cells and monocytes/macrophages, the ability of the same cell populations to respond to ISRAA by producing cytokines, such as interferon (IFN)-γ, as well as the fact that ISRAA is lined up on chromosome 14 on the mouse system where several low molecular mass cytokines are mapped (1). Although ISRAA was identified in the mouse, the alignment has shown that the molecule has conserved regions between many species (2). Furthermore, the function of ISRAA has been found to be dose-dependent, as it has the ability to stimulate the proliferation of human peripheral blood mononuclear cells (hPBMCs) at a low concentration of 50 pg, while a higher concentration of 5 µg has been shown to result in apoptosis (2).…”

“…Although ISRAA was identified in the mouse, the alignment has shown that the molecule has conserved regions between many species (2). Furthermore, the function of ISRAA has been found to be dose-dependent, as it has the ability to stimulate the proliferation of human peripheral blood mononuclear cells (hPBMCs) at a low concentration of 50 pg, while a higher concentration of 5 µg has been shown to result in apoptosis (2).…”

“…Such activities may be induced directly by the effective molecule, e.g., ISRAA, or indirectly by the production of immune mediators, such as cytokines (2). Cytokines are low molecular mass proteins (~5-20 kDa) that are important in cell signaling.…”