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 hematopoiesisspecific G protein ␣-subunit G␣16 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 G␣16 expression and sensitivity to the hemoregulatory peptide (pEEDCK)2 which harbors a structural homology to the effector domain of G␣16. Investigations on blood samples from lymphoma patients undergoing salvage therapy with different cytokine support showed that monitoring of the expression of G␣16 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, G␣16 transcription occurs independently of cell cycle state. In vitro, we could show that G␣16 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 G␣16 and CD34 expressing cells to the granulocyte-derived hemoregulatory peptide (pyroGlu-Glu-Asp-Cys-Lys)2 = (pEEDCK)2 which harbors a G␣16-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 G␣16 may co-operate with (pEEDCK)2 in triggering the cytokine response of immature hematopoietic cells.

Bone marrow stem cell protection from chemotherapy by low–molecular-weight compounds

“…On the other hand, p(EEDCK) 2 appears to mimic IL-6 and interleukin-11 (IL-11) and to synergize with IL-3 and SCF in stimulating the proliferation of HSC. This group also found that G ␣ 16, a G protein tyrosine kinase-like ␣ subunit, shares a sequence homology motif with p(EEDCK) 2 in its effector domain [90]. G ␣ 16 is exclusively expressed on CD34 ϩ hematopoietic cells and is markedly downregulated during differentiation.…”

Effect of the Hemoregulatory Peptide (pEEDCK)2 (pyroGlu‐Glu‐Asp‐Cys‐Lys)2 and MIP‐1α is Reduced in Bone Marrow Cultures from Patients with Chronic Myeloid Leukemia (CML)

“…The hemoregulatory peptide (pEEDCK)2 has the potential to replace the activity of growth factor cocktails in in vitro systems of murine hematopoiesis [13, 14] and to enhance the effect of cytokines such as IL‐3 and SCF on colony outgrowth of human CD34 + cells (stem cells [6]). Considering its activity on hematopoietic cells, the hemoregulatory peptide pEEDCK has some functional similarity to MIP‐1α that is reflected in a structural analogy involving the presence of Cys‐Cys motifs.…”

“…The hemoregulatory peptide dimer was synthesized, purified, and stored as described [6]. In short, the synthesis procedure started with the monomer [11].…”

“…It is expressed in normal and malignant hematopoiesis [5]. Previous data also suggest a functional association of the hemoregulatory peptide with G-protein-mediated signal transduction and indicate that this type of G-protein α-subunit may cooperate with (pEEDCK)2 in triggering the cytokine response of immature hematopoietic cells [6].…”