MLL2/KMT2D and MLL3/KMT2C expression correlates with disease progression and response to imatinib mesylate in chronic myeloid leukemia.

BACKGROUND: Chronic myeloid leukemia (CML) is a clonal myeloproliferative neoplasm whose pathogenesis is linked to the Philadelphia chromosome presence that generates the BCR-ABL1 fusion oncogene. Tyrosine kinase inhibitors (TKI) such as imatinib mesylate (IM) dramatically improved the treatment efficiency and survival of CML patients by targeting BCR-ABL tyrosine kinase. The disease shows three distinct clinical-laboratory stages: chronic phase, accelerated phase and blast crisis. Although patients in the chronic phase respond well to treatment, patients in the accelerated phase or blast crisis usually show therapy resistance and CML relapse. It is crucial, therefore, to identify biomarkers to predict CML genetic evolution and resistance to TKI therapy, considering not only the effects of genetic aberrations but also the role of epigenetic alterations during the disease. Although dysregulations in epigenetic modulators such as histone methyltrasnferases have already been described for some hematologic malignancies, to date very limited data is available for CML, especially when considering the lysine methyltransferase MLL2/KMT2D and MLL3/KMT2C. METHODS: Here we investigated the expression profile of both genes in CML patients in different stages of the disease, in patients showing different responses to therapy with IM and in non-neoplastic control samples. Imatinib sensitive and resistant CML cell lines were also used to investigate whether treatment with other tyrosine kinase inhibitors interfered in their expression. RESULTS: In patients, both methyltransferases were either upregulated or with basal expression level during the chronic phase compared to controls. Interestingly, MLL3/KMT2C and specially MLL2/KMT2D levels decreased during disease progression correlating with distinct clinical stages. Furthermore, MLL2/KMT2D was decreased in patients resistant to IM treatment. A rescue in the expression of both MLL genes was observed in KCL22S, a CML cell line sensitive to IM, after treatment with dasatinib or nilotinib which was associated with a higher rate of apoptosis, an enhanced expression of p21 (CDKN1A) and a concomitant decrease in the expression of CDK2, CDK4 and Cyclin B1 (CCNB1) in comparison to untreated KCL22S control or IM resistant KCL22R cell line, which suggests involvement of p53 regulated pathway. CONCLUSION: Our results established a new association between MLL2/KMT2D and MLL3/KMT2C genes with CML and suggest that MLL2/KMT2D is associated with disease evolution and may be a potential marker to predict the development of therapy resistance.

Overexpression of EZH2 associates with a poor prognosis in chronic lymphocytic leukemia.

EZH2, a histone methyltransferase, is overexpressed in several human tumors, but whether it exerts any impact in chronic lymphocytic leukemia (CLL) remains unknown. We used real time PCR to investigate the expression profile of EZH1 and EZH2 in 59 CLL patients, 10 samples of purified B-cells from healthy donors and 12 normal adult tissues. EZH2 was overexpressed in CLL patients and correlates with high white blood cell count, ZAP-70 expression and chromosomal abnormalities. EHZ1 expression does not correlate with CLL progression. EZH2 overexpression is related to a poor prognosis of CLL and could be a useful tool to assess its aggressiveness.

Altered expression of MLL methyltransferase family genes in breast cancer.

The histone lysine methyltransferases contain a SET domain, which catalyzes the addition of methyl groups to specific lysine residues. The MLL family of genes encodes histone-modifying enzymes with histone 3-lysine 4 methyltransferase activity that can regulate gene transcription. The MLL family exists in multi-protein complexes and has been implicated in a variety of processes including normal development and cell growth. Although some of the MLL family members have already been described to be involved in cancer, a clear relationship of these genes with breast cancer is not determined to date. In the present study, we used quantitative PCR to investigate the expression profile of all five MLL genes [MLL (ALL-1), MLL2, MLL3, MLL4 and MLL5] in 7 breast cancer cell lines, 8 breast tumors and adjacent non-tumor tissues and in 12 normal tissues. We observed a diminished expression of all five genes in the breast cancer cell lines when compared to normal breast tissue. We found a significantly decreased expression of MLL2 in the tumor samples compared to the non-tumor controls. In tumor samples, MLL5 also showed a clear suppression tendency. Among the normal tissues analyzed, all genes showed a markedly higher expression in skeletal muscle and brain. Although further studies are required to determine the exact role of these methyltransferases in cancer development, our results indicate that the suppression of MLL genes, especially MLL2 and 5, take part in modulating breast carcinogenesis. Our assessment of the MLL family gene expression patterns in a diverse set of breast cancer cell lines and in a multitude of tissue types and breast tumors should lead to increasingly detailed information on the involvement of these genes in cancer progression.