In vivo and in vitro effects of cytokines and the hemoregulatory peptide dimer (pEEDCK)2 (pyroGlu-Glu-Asp-Cys-Lys)2 on G alpha 16-positive hematopoiesis

G proteins play an important role in signal transduction from cytokine rece ptors to intracellular effecters via different pathways, eg involving tyros ine kinases. In our previous studies, we demonstrated that mRNA expression of the hematopoiesis-specific G protein alpha-subunit G alpha 16 is a sensi tive marker indicating the appearance of early myeloid and lymphoid progeni tors. This study was designed to investigate cytokine effects on hematopoie sis in vivo and in vitro as reflected by G alpha 16 expression and sensitiv ity to the hemoregulatory peptide (pEEDCK)2 which harbors a structural homo logy to the effector domain of G alpha 16. Investigations on blood samples from lymphoma patients undergoing salvage therapy with different cytokine s upport showed that monitoring of the expression of G alpha 16 mRNA which ap pears to play a role in cytokine signalling via tyrosine kinases was a valu able 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 alpha 16 transcription occurs independentl y of cell cycle state. In vitro,we could show that G alpha 16 was also a va luable marker for confirming the immature state of ex vivo expanded blood s tem cells from patients. A further part of the study was focused on the res ponse of G alpha 16 and CD34 expressing cells to the granulocyte-derived he moregulatory peptide (pyroGlu-Glu-Asp-Cys-Lys)2 = (pEEDCK)2 which harbors a G alpha 16-homologous sequence motif. Results obtained from in vitro assay s which involved estimation of colony outgrowth from CD34-positive cells sh owed that the effect of (pEEDCK)2 on CD34 cells enhanced the effect of IL-3 or SCF. These data indicate that Ga16 may co-operate with (pEEDCK)2 in tri ggering the cytokine response of immature hematopoietic cells.