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Molecular mechanisms of apoptosis induced by an immunomodulating peptide on human monocytes
J A Osés-Prieto1, N López-Moratalla, E Santiago
1Department of Biochemistry, University of Navarra, Pamplona, Spain.
Abstract:
A short immunomodulating peptide (Pa) containing a defined structural motif present in a number of extracellular matrix proteins and autoantigens was found to stimulate human monocytes. Pa-induced apoptosis of isolated monocytes, as indicated by internucleosomal DNA cleavage, increased annexin V binding capacity and cleavage of caspase substrates, such as poly(ADP)ribosylpolymerase. In addition, Bcl-2 protein levels were downregulated during Pa-induced cell death. Nuclear extracts of monocytes incubated with Pa showed higher neutral, Ca(2+)-dependent DNase activity than those obtained from nontreated monocytes. Caspase inhibitors prevented Pa-induced apoptosis, Bcl-2 depletion, and DNase activation. Treatment of monocytes with Pa activated c-Jun N-terminal kinases and p38 kinase, in an acidic sphingomyelinase- and caspase-dependent fashion. Pa-induced apoptosis was blocked by selective inhibitors of p38 kinase (SB203580) and acidic sphingomyelinase (SR33557). These results indicate that JNK and p38 kinase stimulation as well as monocyte apoptosis induced by Pa could depend, at least in part, on early activation of acidic sphingomyelinase.
Insights
A short peptide (Pa) stimulates human monocytes, triggering programmed cell death (apoptosis). This process involves specific enzymes and signaling pathways, highlighting a novel mechanism in monocyte regulation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Extracellular matrix proteins and autoantigens can modulate immune cell function.
- The immunomodulating peptide (Pa) shares structural motifs with these proteins.
- Human monocytes play a critical role in immune responses.
Purpose of the Study:
- To investigate the effects of the immunomodulating peptide (Pa) on human monocytes.
- To elucidate the molecular mechanisms underlying Pa-induced monocyte apoptosis.
- To identify key signaling pathways involved in Pa-mediated immune cell modulation.
Main Methods:
- Monocyte isolation and incubation with Pa.
- Assessment of apoptosis using DNA fragmentation, annexin V binding, and caspase substrate cleavage.
- Analysis of Bcl-2 protein levels and neutral Ca(2+)-dependent DNase activity.
- Investigation of kinase activation (JNK, p38) and sphingomyelinase activity.
- Use of specific inhibitors for caspases, p38 kinase, and acidic sphingomyelinase.
Main Results:
- Pa induced apoptosis in isolated human monocytes, evidenced by DNA cleavage and altered protein levels.
- Pa treatment led to the activation of c-Jun N-terminal kinases (JNK) and p38 kinase.
- Apoptosis, Bcl-2 depletion, and DNase activation were prevented by caspase inhibitors.
- Early activation of acidic sphingomyelinase was observed.
- Pa-induced apoptosis was blocked by p38 kinase and acidic sphingomyelinase inhibitors.
Conclusions:
- The immunomodulating peptide (Pa) induces apoptosis in human monocytes through caspase-dependent and kinase-dependent pathways.
- Activation of acidic sphingomyelinase, JNK, and p38 kinase are crucial early events in Pa-induced monocyte apoptosis.
- These findings reveal a novel mechanism of immunomodulation involving specific peptide-induced cell death pathways.