Altered erythrocyte protein kinase C activity and membrane protein phosphorylation in chronic myelogenous leukemia

Role of calcium-dependent protein kinases in chronic myeloid leukemia: combined effects of PKC and BCR-ABL signaling on cellular alterations during leukemia development

Calcium-dependent protein kinases (PKCs) function in a myriad of cellular processes, including cell-cycle regulation, proliferation, hematopoietic stem cell differentiation, apoptosis, and malignant transformation. PKC inhibitors, when targeted to these pathways, have demonstrated efficacy against several types of solid tumors as well as leukemia. Chronic myeloid leukemia (CML) represents 20% of all adult leukemia. The aberrant Philadelphia chromosome has been reported as the main cause of CML development in hematopoietic stem cells, due to the formation of the BCR-ABL oncogene. PKCs and BCR-ABL coordinate several signaling pathways that are crucial to cellular malignant transformation. Experimental and clinical evidence suggests that pharmacological approaches using PKC inhibitors may be effective in the treatment of CML. This mini review summarizes articles from the National Center for Biotechnology Information website that have shown evidence of the involvement of PKC in CML.

Alterations in skeletal protein, distribution of PKCalpha, and level of phospholipids in erythrocyte membranes of women with primary breast cancer

The aim of our work was to study the influence of primary breast cancer on mature erythrocyte membranes. Blood was sampled from 29 women with primary breast cancer, aged 35-86 years, in different stages of clinical progression of the disease. In red blood cell membranes an increase of phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-diphosphate levels was observed. These changes were accompanied by a decrease in phospholipase C activity. Simultaneously, a significant decrease in concentration of phosphatidylserine, sphingomyelin, and phosphatidylinositol was found. Quantitative protein evaluation showed an increase in band 4.1 protein content with no changes in the level of constitutive PKCalpha responsible for the phosphorylation of this protein and its affinity to glycophorine C. In parallel a greater increase of PKCalpha translocation after PMA treatment compared to controls was observed. Possible oxidative damage of erythrocyte membranes indicated by an increase in malonyldialdehyde level and decrease in SH-group content as well as by an increase in the w/ ratio was documented. From the results it is concluded that primary breast cancer seems to affect the membranes of mature erythrocytes.

Reversible erythrocyte skeleton destabilization is modulated by beta-spectrin phosphorylation in childhood leukemia

The erythrocyte skeleton plays an essential role in determining the shape and deformability of the red cell. Disruption of the interaction between components of the red cell membrane skeleton may cause loss of structural and functional integrity of the membrane. Several observations based on studies in vitro strongly suggest that phosphorylation may modify interactions between proteins, leading to a reduced affinity. In particular, increased phosphorylation of beta-spectrin decreases membrane mechanical stability. In order to investigate the presence of membrane protein defects we investigated the erythrocyte membrane protein composition and phosphorylation in 22 children with leukemia at diagnosis and during the remission phase. Sixteen children had acute lymphoblastic leukemia (ALL), three had chronic myeloid leukemia (CML) and three had acute myeloid leukemia (AML). Ten patients (eight ALL and two CML) displayed elliptocytosis and poikilocytosis, an increase of spectrin dimers (41.8 +/- 15.6) and an enhanced phosphorylation of beta-spectrin (108 +/- 15%) at diagnosis. These alterations disappeared during the remission phase. This is the first demonstration of a reversible erythrocyte membrane alteration in leukemia. Since the beta-spectrin phosphate sites are located near the C-terminal region and close to the head of the beta-chain that is involved in dimer-dimer interaction, we supposed that the beta-chain phosphorylation has an effect upon the interactions between spectrin dimers, ie the tetramerization process. The weakening of this process should be responsible for the presence of elliptocytes and poikilocytes as reported in hereditary elliptocytosis and pyropoikilocytosis.

Possible involvement of protein kinase C in the aberrant regulation of erythropoiesis in polycythemia vera

To examine the possible involvement of protein kinase C (PKC) in the regulation of aberrant erythropoiesis of polycythemia vera (PV), we investigated the effects of PKC inhibitors on in vitro burst-forming unit of erythroid (BFU-E)-derived colony formation by bone marrow (BM) and peripheral blood (PB) cells obtained from five PV patients. 1-(Isoquinoline-sulfonyl)-2-methylpiperazine dihydrochloride (H-7), an inhibitor of PKC, suppressed the colony formation by BM and PB cells of PV patients in a dose-dependent manner, similar to those in the normal individuals. However, the 50% inhibitory concentrations (IC50) of H-7 in PV BM and PB cells were significantly higher than those in normal BM and PB cells, respectively. The BFU-E-derived colony formation by PV BM and PB cells was also less affected by Staurosporine, another PKC inhibitor, than those in a normal subject. Furthermore, in the study of PV, the IC50 of endogenous colonies formed in the absence of erythropoietin was much higher than that of colonies formed by the stimulation of erythropoietin. By contrast, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide dihydrochloride (HA1004), a cyclic AMP-dependent kinase inhibitor, did not have such inhibitory effects. These findings suggest that PKC, as a second messenger, is involved in the regulation of aberrant erythropoiesis of PV.