Expression Profile of PIP Kinases During In Vitro Human Erythropoiesis

Abstract 2079

Phosphatidylinositol phosphate kinases (PIPKs) are a family of lipid kinase enzymes that produce the second messenger PI4,5P2 (phosphatidylinositol 4,5-biphosphate), which plays an important role in the regulation of a variety of cellular activities, including gene expression. PIPKs are classified into 3 subfamilies — PIPK I (a, b, g), PIPK II (a, b, g) and PIPK III — which are functionally distinct and are located in different subcellular compartments. In a recent study in our laboratory, the PIPKIIa gene was differentially expressed in reticulocytes from 2 siblings with hemoglobin (Hb) H disease who had the same genotype (-a^3.7/–^SEA). Expression of both the PIPKIIa and b-globin genes were higher in the patient with the higher Hb H level, suggesting a possible relationship between PIPKIIa and the production of globins, particularly b-globin. In light of these findings, the aim of this study was to determine the gene expression profiles of PIPKs (I and II - with their isoforms a, b and g - and III) during erythropoiesis in peripheral blood hematopoietic CD34⁺ cell culture from 11 healthy volunteers and 6 patients with hemoglobinopathies [2 with a-thalassemia (Hb H disease), 2 with b-thalassemia (homozygous for the IVS-I-6-T-C mutation) and 2 with sickle cell anemia] using quantitative real time PCR (qRT-PCR) and to compare these profiles with the gene expression profiles of a-, b- and g-globins on the 7^th, 10^th and 13^th days of the erythroid culture. In the cell culture from the normal group, expression of the PIPKIIa and other PIPK genes increased during erythroid differentiation, coinciding with the expression profiles of globin genes and showing in particular that a-globin has a significant effect on PIPKIIa (p<0.0001), as the PIPKIIa on a-globin gene (p=0.0002). In the patients, the expression profile of the PIPKIIa gene also increased during differentiation, whereas the results for the other PIPK genes varied. However, mRNA levels differed between patients, indicating greater complexity in individuals with hemoglobinopathies. PIPKIIa expression level was elevated in the culture from one of the a-thalassemia patients (approximately 12 times higher than in the corresponding control) but was lower than the control in one of the b-thalassemia patients. Expression levels of this gene also varied among sickle cell patients. This is the first study of the gene expression profiles of these kinases during in vitro human erythropoiesis. We identified a standard pattern of gene expression for PIPKs, and PIPKIIa in particular, a gradual increase in expression during erythroid differentiation, similar to the pattern for globin genes. This suggests that PI4,5P2, as an important secondary messenger involved in the regulation of gene expression, may play an important role in the regulation of globin gene expression and the normal process of Hb synthesis in red blood cells. Although our results varied between patients, highlighting the complexity of the regulatory systems involved in Hb production, they reinforce the hypothesis of a relationship between PIPKIIa and globin expression. This work was supported by FAPESP, CNPq and CAPES.