Nuclear translocation of immulectin-3 stimulates hemocyte proliferation

Immulectin-3 (IML-3) is a C-type lectin from the tobacco hornworm Manduca sexta that contains a motif (NWGV) similar to the BH1 motif (NWGR) of the mammalian galectin-3. IML-3 is synthesized in fat body and secreted into hemolymph, but can be translocated into hemocytes. In this study, we showed that IML-3 was predominantly localized to the nucleus of hemocytes and some metaphase, anaphase and telophase hemocytes from M. sexta larvae injected with bacterial lipopolysaccharide (LPS). IML-3 was detected in the membrane and soluble extracts of hemocytes, suggesting that it may be translocated into hemocytes via receptor-mediated endocytosis. To investigate the role of IML-3 translocation to the nucleus, we expressed recombinant wild-type IML-3 and a deletion mutant ΔIML-3 that has the NWGV motif deleted in Drosophila S2 cells. We found that recombinant wild-type IML-3, but not ΔIML-3, was localized to the nucleus of some S2 cells and also detected in the nuclear extract. Expression of recombinant wild-type IML-3, but not ΔIML-3 or GFP, increased the number of proliferating S2 cells. Our results suggest that nuclear translocation of IML-3 may stimulate hemocyte proliferation.