Stem cell stimulation in vitro by the dekapeptide (pEEDCK)2: a single-factor alternative for multifactor cocktails

Insertion of foreign genes into cellular DNA requires (at least one round of) DNA replication. Since hemopoietic stem cells do not divide rapidly, numerous semi-empirically designed multifactor cocktails have been used to stimulate them. In an attempt to find an alternative to this approach we have investigated the effects of the stem cell stimulatory peptide (pGlu-Glu-Asp-Glys-Lys)2, (pEEDCK)2, on progenitor output in murine long-term bone marrow cultures (LTBMC). (pEEDCK)2 may act by inducing growth factor production in stromal cells. Addition of (pEEDCK)2 to LTBMCs resulted in a three-fold increase in CFU-GM production. For showing an effect of (pEEDCK)2 on primitive hemopoietic cells (long-term-culture initiating cells, (LTC-IC)) LTBMCs were depleted of rapidly dividing progenitors by 5-Fluoro-Uracil (5-FU). LTC-IC survive and repopulate the culture with new CFU-GM. (pEEDCK)2 greatly enhanced this process (eight-fold in the second week after 5-FU). Enhanced progenitor production was observed for several weeks even after discontinuation of (pEEDCK)2 additions to the cultures (100-fold, five weeks after 5-FU, three weeks after end of peptide additions). This increase in progenitor production resulted in increased numbers of total nucleated cells. Our results suggest that (pEEDCK)2 may be a useful alternative for multifactor cocktails when proliferation of primitive stem-cell-like cells is required, as in gene therapy and transplantation. Our experiments also indicate that the redox equilibrium between (stem cell inhibitory) monomeric pEEDCK and (stem cell stimulatory) dimeric (pEEDCK)2, which are both endogenous constituents of LTBMCs may play a role in physiological stem cell regulation.