G9a Correlates with VLA-4 Integrin and Influences the Migration of Childhood Acute Lymphoblastic Leukemia Cells.

Elena Madrazo,África González-Murillo,David Ruano,Carmen Sánchez-Valdepeñas,Lorea Abad,Estefanía Alonso-Gómez,Manuel Ramírez,Javier Redondo-Muñoz

doi:10.3390/cancers10090325

Abstract

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. As ALL progresses, leukemic cells cross the endothelial barrier and infiltrate other tissues. Epigenetic enzymes represent novel therapeutic targets in hematological malignancies, and might contribute to cells’ capacity to migrate across physical barriers. Although many molecules drive this process, the role of the nucleus and its components remain unclear. We report here, for the first time, that the expression of G9a (a histone methyltransferase related with gene silencing) correlates with the expression of the integrin subunit α4 in children with ALL. We have demonstrated that G9a depletion or its inhibition with BIX01294 abrogated the ability of ALL cells to migrate through an endothelial monolayer. Moreover, G9a-depleted and BIX01294-treated cells presented bigger nuclei and more adherent phenotype than control cells on endothelial monolayers. Blocking G9a did not affect the cell cytoskeleton or integrin expression of ALL cell lines, and only its depletion reduced slightly F-actin polymerization. Similarly to the transendothelial migration, G9a inhibition impaired the cell migration induced by the integrin VLA-4 (α4β1) of primary cells and ALL cell lines through narrow spaces in vitro. Our results suggest a cellular connection between G9a and VLA-4, which underlies novel functions of G9a during ALL cell migration.

Highlights

Acute lymphoblastic leukemia (ALL), the most common cancer in children, is characterized by the accumulation of hematopoietic B- or T-cell precursors, which eventually infiltrate the bone marrow or thymus and secondary organs, resulting in leukemia progression [1,2]
Our observations indicate that targeting G9a clearly affects ALL cell migration, which might contribute to leukemia infiltration and dissemination through the patient’s body
We provide the first evidence for the functional involvement of G9a activity in the migration of primary ALL cells from patients

Summary

Introduction

Acute lymphoblastic leukemia (ALL), the most common cancer in children, is characterized by the accumulation of hematopoietic B- or T-cell precursors, which eventually infiltrate the bone marrow or thymus and secondary organs, resulting in leukemia progression [1,2]. Risk-tailored therapy protocols can cure most children with ALL but non-responding and relapsed pediatric ALL patients (20% of total) have poor. ALL cells present specific genetic and epigenetic changes, which open new avenues to stratify patients and develop more effective therapies [6,7]. It has been reported that the methylation of specific histones is linked to cancer cell invasion [8,9]. One of these enzymes, the histone methyltransferase G9a catalyzes H3K9 methylation (a heterochromatin marker) [10], and is critical in lymphocyte development and leukemogenesis [11]; and its inhibition promotes apoptosis in acute leukemias [12]. VLA-4 adhesion promotes G9a activity and H3K9 methylation during Jurkat (a T-ALL cell line) and normal lymphocyte cell migration [17]; the interplay between VLA-4 and G9a, and how they contribute to ALL dissemination, has not been described before

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