Carboxy-terminal fragment of osteogenic growth peptide regulates myeloid differentiation through RhoA

The carboxy-terminal fragment of osteogenic growth peptide, OGP(10-14), is a pentapeptide with bone anabolic effects and hematopoietic activity. The latter activity appears to be largely enhanced by specific growth factors. To study the direct activity of OGP(10-14) on myeloid cells, we tested the pentapeptide proliferating/differentiating effects in HL60 cell line. In this cell line, OGP(10-14) significantly inhibited cell proliferation, and enhanced myeloperoxidase (MPO) activity and nitroblue tetrazolium reducing ability. Moreover, it induced cytoskeleton remodeling and small GTP-binding protein RhoA activation. RhoA, which is known to be involved in HL60 differentiation, mediated these effects as shown by using its specific inhibitor, C3. Treatment with GM-CSF had a comparable OGP(10-14) activity on proliferation, MPO expression, and RhoA activation. Further studies on cell proliferation and RhoA activation proved enhanced activity by association of the two factors. These results strongly suggest that OGP(10-14) acts directly on HL60 cells by activating RhoA signaling although other possibilities cannot be ruled out.     

Diallyl disulfide down‐regulates calreticulin and promotes C/EBPα expression in differentiation of human leukaemia cells

Diallyl disulfide (DADS), the main active component of the cancer fighting allyl sulfides found in garlic, has shown potential as a therapeutic agent in various cancers. Previous studies showed DADS induction of HL‐60 cell differentiation involves down‐regulation of calreticulin (CRT). Here, we investigated the mechanism of DADS‐induced differentiation of human leukaemia cells and the potential involvement of CRT and CCAAT enhancer binding protein‐α (C/EBPα). We explored the expression of CRT and C/EBPα in clinical samples (20 healthy people and 19 acute myeloid leukaemia patients) and found that CRT and C/EBPα expressions were inversely correlated. DADS induction of differentiation of HL‐60 cells resulted in down‐regulated CRT expression and elevated C/EBPα expression. In severe combined immunodeficiency mice injected with HL‐60 cells, DADS inhibited the growth of tumour tissue and decreased CRT levels and increased C/EBPα in vivo. We also found that DADS‐mediated down‐regulation of CRT and up‐regulation of C/EBPα involved enhancement of reactive oxidative species. RNA immunoprecipitation revealed that CRT bound C/EBPα mRNA, indicating its regulation of C/EBPα mRNA degradation by binding the UG‐rich element in the 3′ untranslated region of C/EBPα. In conclusion, the present study demonstrates the C/EBPα expression was correlated with CRT expression in vitro and in vivo and the molecular mechanism of DADS‐induced leukaemic cell differentiation.