SUZ12 is a candidate target of the non‐canonical WNT pathway in the progression of chronic myeloid leukemia

Abstract

Polycomb proteins form multiprotein complexes that repress target genes by chromatin remodeling. In this work, we report that the SUZ12 polycomb gene is over-expressed in bone marrow samples of patients at the blastic phase of chronic myeloid leukemia. We also found a direct interaction between polycomb group genes and the WNT signaling pathway in chronic myeloid leukemia transformation. Electrophoretic mobility shift assay (EMSA), Chromatin immunoprecipitation assay (ChIP), and mass spectrometry assays identified noncanonical WNT pathway members, such as WNT5A and WNT11, bound to the SUZ12 promoter. Immunohistochemistry and immunofluorescence with WNT5A and WNT11 antibodies confirmed nuclear localization. Knockdown of WNTs 1, 5A, and 11 with RNAi approaches showed that WNT members are capable of activating SUZ12 transcription with varying promoter affinities. Finally, we suggest that SUZ12 is blocking cellular differentiation, as SUZ12 knockdown release differentiation programs in chronic myeloid blastic phase (CML-BP) transformed cell line.

A feedback loop that regulates the expression of polycomb group protein Suz12 via non-canonical WNT signaling pathway in blast crisis of chronic myeloid leukemia

“…Besides, the present research has shown that knock-down of Suz12 by small interfering RNA (siRNA) produces a significant decrease of 98% in the expression of Kaiso in K562 cells, the first established human immortalized myelogenous leukemia line [13]. Evidence presented above suggests that, at least, The genes Wnt11 and Wnt5a up-regulate Suz12 expression (supressor of zeste 12) acting in the nucleus as transcriptional factors, as described previously by [15]. (b) Suz12 activates the transcription of Kaiso, as described here in this article and (c) Kaiso and TCF/LEF cooperate to repress the transcription of Wnt11 as described by [14].…”

“…Previously Pizzatti et al, reported that both Wnt5a and Wnt11 upregulate the expression of Suz12 by acting as transcription factors in the cell nucleus [15] (Figure 2a). The real importance of that positive regulation should be understood in the context of leukemia patients who present, in the blast phase, a significant increase in the expression of Suz12.…”

“…Consistent with the rupture of regulatory loop equilibrium the PcG proteins overexpression seems to be a trademark for some types of tumors [5,6,9,10,20]. Particularly, the increase of Suz12 is one of the main features found in K562 cells used as the cellular model of chronic myeloid leukemia in a blast crisis [15]. Therefore, this epigenetic regulatory loop can have profound implications for future therapeutic strategies not only in chronic myeloid leukemia but also in other tumor types.…”

“…As it was previously reported, the RNAi knock-down of Kaiso in K562 cells improves survival and proliferation [3]. On the other hand, we know that the expression of Suz12 is significantly increased in various types of cancer [15]. Therefore, we decided to evaluate the existence of a transcriptional regulation independent of repression of Suz12 over Kaiso.…”

“…Thus, the abnormal PcG expression leads to a loss of cell identity, improves a proliferative ability and increases the migratory/invasive potential. These proteins are often aberrantly expressed in cancer cells and, in particular, Suz12, EZH2 and BMI1 are well known to be over-expressed in a certain number of human tumors including breast cancer, prostate cancer and chronic myeloid leukemia [5,6,9,10,15,20]. The principal mechanism by which PcG proteins promote tumorigenesis and metastasis seems to be senescence bypass [1,8] and increase cell survival [6,7].…”