Connexin expression in human acute myeloid leukemia cells: Identification of patient subsets based on protein and global gene expression profiles

Abstract

Bone marrow stromal cells support both normal and malignant hematopoiesis. Τhis support is mediated through the local cytokine network and by direct cell-cell interactions mediated via adhesion molecules and the formation of gap junctions by connexins. Previous studies on connexins in human acute myeloid leukemia (AML) have mainly focused on the investigation of leukemia cell lines. In the present study, we therefore investigated the expression of various connexins at the protein (i.e., cell surface expression) and mRNA level in primary human AML cells. The cell surface expression of the connexins, Cx26, Cx32, Cx37, Cx43 and Cx45, varied considerably between patients, and detectable levels were observed only for subsets of patients. On the whole, Cx43 and Cx45 showed the highest cell surface expression. Connexin expression was dependent on AML cell differentiation, but showed no association with cytogenetic abnormalities or mutations of the fms-related tyrosine kinase 3 (FLT3) or nucleophosmin (NPM)‑1 genes. By contrast, only Cx45 showed a significant variation between patients at the mRNA level. A high Cx45 expression was associated with the altered regulation of the mitogen-activated protein kinase (MAPK) pathway and the release of pro-inflammatory cytokines [interleukin (IL)-17, tumor necrosis factor (TNF), interferon-γ], whereas a low Cx45 expression was associated with the altered regulation of protein functions (i.e., ligase activity, protein folding and catabolism). There was no significant correlation observed between the connexin mRNA and protein levels. Thus, differences in connexin expression can be used to subclassify AML patients. Differences in connexin cell surface expression profiles are not reflected at the mRNA level and have to be directly examined, whereas variations in Cx45 mRNA expression are associated with differences in cell signaling and the regulation of protein functions.

Disruption of gap junctions attenuates acute myeloid leukemia chemoresistance induced by bone marrow mesenchymal stromal cells

“…Cx43 and Cx32 are expressed in OCIM2 and OCI-AML3 cell lines and the proliferative capacity of OCIM2 cells is related to the expression level of Cx43, suggesting its role in the regulation of cell proliferation [28]. Reikvam et al have described the expression pattern of five different Cxs (Cx26, Cx32, Cx37, Cx43, and Cx45) in primary AML cells [29], and reported a high expression of Cx43 and Cx45, particularly in the most differentiated stages such as FAB M4 and M5) [30]. These studies support a role of Cxs as regulators of interactions between AML cells and their microenvironment.…”

Enhanced generation of human induced pluripotent stem cells by ectopic expression of Connexin 45

“…Second, ectopic overexpression of a new gene during reprogramming may increase tumorigenicity of iPSCs. Reikvam et al reported that CX45 expression show a wide variation between human myeloid leukemia cells at the mRNA level and a high CX45 expression was associated with the altered regulation of the mitogen-activated protein kinase (MAPK) pathway, whereas a low CX45 expression was associated with the altered regulation of protein functions 42 . While in another study, it is reported that CX45 expression was reduced in colorectal carcinomas compared to normal tissue samples 43 .…”

Gap Junctions in the Bone Marrow Lympho-Hematopoietic Stem Cell Niche, Leukemia Progression, and Chemoresistance

“…The transcript of several connexins including Cx26, Cx32, Cx37, Cx43, and Cx45 has been observed in primary human AML blasts, and the higher surface expression of Cx43 and Cx45 was found in most differentiated FAB M4 and M5 cells [163]. Higher expression of Cx45 associated with the altered regulation of the mitogen-activated protein kinase (MAPK) pathway and the release of pro-inflammatory cytokines IL-17, TNFα, and IFNγ, resulted in a pro-tumorigenic environment and protected AML cells from chemotherapy.…”

“…Higher expression of Cx45 associated with the altered regulation of the mitogen-activated protein kinase (MAPK) pathway and the release of pro-inflammatory cytokines IL-17, TNFα, and IFNγ, resulted in a pro-tumorigenic environment and protected AML cells from chemotherapy. Conversely, expression of Cx32 and Cx35 was comparable in both undifferentiated (FAB M0, M1, and M2) and differentiated (FAB M4 and M5) AML cells [163]. Furthermore, higher expression of Cx25 and Cx40 in acute lymphoblastic leukemia (ALL) and AML cell lines, as well as in AML patient's cells play an important role in leukemia cell communication and chemoresistance.…”