Two non-cytotoxic type 2 ribosome-inactivating proteins (Sambucus Sieboldiana lectin and Sambucus Nigra lectin) lead neurosphere cells to caspase-independent apoptosis

Abstract

We found a new phenomenon of cell damage and/or cell death of almost all types of neurosphere cells derived from telencephalons of mouse embryos. The cell damage/death was induced by non-cytotoxic type 2 ribosome-inactivating proteins: Sambucus Sieboldiana lectin (SSA) and Sambucus Nigra lectin (SNA). Self-renewal and aggregation of the neurosphere cells were inhibited under the presence of SSA or SNA. These lectins led the neurosphere cells to cell damage by making them lose their proliferation capacity. It was found that Siaα2-6Galβ1-4GlcNAc or Siaα2-6Gal on the membrane of neurosphere cells play an important role in the induction of cell damage of neurosphere cells. Moreover, despite the fact that most of the neurosphere cells cultured under the presence of SSA or SNA were Annexin V positive, these cells were not identified by DNA ladder assays. Additionally, the cells were not rescued from cell death even under the presence of a pan-caspase inhibitor. These findings imply that cell death of neurosphere cells caused by SSA or SNA is caspase-independent apoptosis via an exogenous pathway. SSA and SNA recognition molecules were detected as 39 and 42 kDa glycoproteins on the membrane of neurosphere cells.