DUSP16 is an epigenetically regulated determinant of JNK signalling in Burkitt's lymphoma.
BACKGROUND
The mitogen-activated protein kinase (MAPK) phosphatases or dual specificity phosphatases (DUSPs) are a family of proteins that catalyse the inactivation of MAPK in eukaryotic cells. Little is known of the expression, regulation or function of the DUSPs in human neoplasia.


METHODS
We used RT-PCR and quantitative PCR (qPCR) to examine the expression of DUSP16 mRNA. The methylation in the DUSP16 CpG island was analysed using bisulphite sequencing and methylation-specific PCR. The activation of MAPK was determined using western blotting with phospho-specific antibodies for extra-cellular signal-related kinase (ERK), p38 and c-Jun N-terminal kinase (JNK). The proliferation of cell lines was assessed using the CellTiter 96 Aqueous One assay.


RESULTS
The expression of DUSP16, which inactivates MAPK, is subject to methylation-dependent transcriptional silencing in Burkitt's Lymphoma (BL) cell lines and in primary BL. The silencing is associated with aberrant methylation in the CpG island in the 5' regulatory sequences of the gene blocking its constitutive expression. In contrast to BL, the CpG island of DUSP16 is unmethylated in other non-Hodgkin's lymphomas (NHLs) and epithelial malignancies. In BL cell lines, neither constitutive nor inducible ERK or p38 activity varied significantly with DUSP16 status. However, activation of JNK was increased in lines with DUSP16 methylation. Furthermore, methylation in the DUSP16 CpG island blocked transcriptional induction of DUSP16, thereby abrogating a normal physiological negative feedback loop that limits JNK activity, and conferred increased cellular sensitivity to agents, such as sorbitol and anthracycline chemotherapeutic agents that activate JNK.


CONCLUSIONS
DUSP16 is a new epigenetically regulated determinant of JNK activation in BL.
Lee
S
S
Laboratory of Cancer Genetics and Epigenetics, Breakthrough Breast Cancer, Institute of Cancer Research, Fulham Road, London, UK.
Syed
N
N
Taylor
J
J
Smith
P
P
Griffin
B
B
Baens
M
M
Bai
M
M
Bourantas
K
K
Stebbing
J
J
Naresh
K
K
Nelson
M
M
Tuthill
M
M
Bower
M
M
Hatzimichael
E
E
Crook
T
T
D002051:Burkitt Lymphoma / Q000235:genetics*; D045744:Cell Line, Tumor; D019175:DNA Methylation; D054637:Dual-Specificity Phosphatases / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D054639:Mitogen-Activated Protein Kinase Phosphatases / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction
D048031:JNK Mitogen-Activated Protein Kinases; D054639:Mitogen-Activated Protein Kinase Phosphatases; C439065:DUSP16 protein, human; D054637:Dual-Specificity Phosphatases