In vivo and in vitro effects of cytokines and the hemoregulatory peptide dimer (pEEDCK)2 (pyroGlu-Glu-Asp-Cys-Lys)2 on Gα16-positive hematopoiesis

Abstract

G proteins play an important role in signal transduction from cytokine receptors to intracellular effectors via different pathways, eg involving tyrosine kinases. In our previous studies, we demonstrated that mRNA expression of the hematopoiesis-specific G protein α-subunit Gα16 is a sensitive marker indicating the appearance of early myeloid and lymphoid progenitors. This study was designed to investigate cytokine effects on hematopoiesis in vivo and in vitro as reflected by Gα16 expression and sensitivity to the hemoregulatory peptide (pEEDCK)2 which harbors a structural homology to the effector domain of Gα16. Investigations on blood samples from lymphoma patients undergoing salvage therapy with different cytokine support showed that monitoring of the expression of Gα16 mRNA which appears to play a role in cytokine signalling via tyrosine kinases was a valuable complementation to CD34 screening for analyzing hematopoietic recovery after chemotherapy. We demonstrated that in contrast to CD34 which is only expressed in quiescent cells, Gα16 transcription occurs independently of cell cycle state. In vitro, we could show that Gα16 was also a valuable marker for confirming the immature state of ex vivo expanded blood stem cells from patients. A further part of the study was focused on the response of Gα16 and CD34 expressing cells to the granulocyte-derived hemoregulatory peptide (pyroGlu-Glu-Asp-Cys-Lys)2 = (pEEDCK)2 which harbors a Gα16-homologous sequence motif. Results obtained from in vitro assays which involved estimation of colony outgrowth from CD34-positive cells showed that the effect of (pEEDCK)2 on CD34 cells enhanced the effect of IL-3 or SCF. These data indicate that Gα16 may co-operate with (pEEDCK)2 in triggering the cytokine response of immature hematopoietic cells.