ECTOPIC PLACENTAL-LIKE ALKALINE PHOSPHATASE (PLAP) REPROGRAMMING BY VITAMIN E IN CML BLAST CRISIS LEUKEMIC K562 CELLS

L. P. Shvachko*

ABSTRACT

Bagraund: Placental-like alkaline phosphatase (PLAP)-1ike enzymes are expressed by many tumors and can be detected in sera of patients with various cancers. Their ectopic expression has been considered to be potentially useful as tumor marker. Indeed, elevated levels of PLAP were found in 43% of seminomas and in 75% of recurrent metastatic tumors. However, the biological background of the role of this aberrant alkaline phosphatase in cancer progression is still unclear. We have focused on the study of the biological role of PLAP in leukemogenesis on the model of chronic myeloid leukemia (CML) K562 cells. Objective: The aim of the study was to attempt to use vitamin E for LSC reprogramming by inducing CEBP alpha (CCAAT/enhancer-binding protein α) and G-CSFR (granulocyte colony stimulating factor receptor) analyzing aberrant PLAP as biomarker of LSC phenotype. Methods: RNA extracted from K562 cells cultured with vitamin E was converted to for quantitative SYBR Green qRT-PCR analysis using primers to tissue nonspecific alkaline phosphatase (TNAP) and C/EBP alpha and G-CSFR respectively. Samples were cycled using the standard SYBR Green protocol on Q5 Bio-Rad StepOne qPCR instrument and analyzed using the comparative cycle threshold (CT) method to obtain relative mRNA expression. Amplicon (410 bp) was eluted from agarose gel (2.5%) and DNA- sequenced. Results: The progression of CML to blast crisis is correlated with both down-modulation of TNAP and C/EBP alpha as master regulator of granulocytic differentiation in myelopoesis. We have observed the ectopic expression of mRNA PLAP gene in K562 cells by real-time RT-PCR. We founded by sequencing that PLAP gene corresponds to embryonic type of placental alkaline phosphatase (EPLAP) and have no gene homology with tissue placental alkaline phosphatase (PAP) that was absent in K562. Vitamin E decreases the mRNA PLAP expression level and increases the mRNA TNAP gene expression. Moreover, along with down-regulation of aberrant PLAP and up-regulation of TNAP, vitamin E in a dose of 100 µM increases mRNA expression of transcription factor C/EBP alpha and G-CSFR. It was reported that osteoblast-expressed TNAP is a biomarker of HSCs and directly associated with HSC hematopoiesis in bone marrow (BM). We have proposed that loss of TNAP in BM HSC niche may contribute into CML pathogenesis, suggesting the impairment of bone marrow mesenchymal stem cell (BM MSC) – derived osteoblast differentiation. The aberrant PLAP in K562 cells seems to differ from tissue TNAP and tissue placental alkaline phosphatase. Conclusion. EPLAP may be considered as a putative target in differentiation therapies in myeloid leukemias. Our findings suggest the potential role of vitamin E in adjuvant therapy of lelukemia as the inducer of differentiation potential of K562 leukemic cells through decreasing ectopic EPLAP along with induction of granulopoiesis factors CEBP alpha/G-CSFR. We have declared that embryonic PLAP is pluripotent LSC-associated biomarker in contrast of TNAP as multipotent HSC-associated biomarker. Vitamin E may be putative modulator of LSCs reprogramming in biotherapies of CML.

Keywords: EPLAP may be considered as a putative target in differentiation therapies in myeloid leukemias.