MYD88 is an adaptor protein through which most of the Toll-like receptors (TLRs) and receptors for IL-1 and IL-18 cytokines signal coordinates the assembly of a multisubunit signaling complex, including IL-1 receptor- associated kinase (IRAK) 1 and IRAK4, and also signals to JAK-STAT 3 signaling and to activation pathways and transcription factors, such as the NF-kB.
The genetics and pathogenesis of Waldenstrom macroglobulinemia (WM), are not fully understood A whole exome–sequencing study of 31 WM patients suggested a high frequency of MYD88 L265P mutation in WM. aim to analyze MYD88 mutation in WM and to characterize the clinical significance of this genetic alteration in a cohort of 67 WM patients.
whole-genome sequencing of bone marrow LPL cells in 30 patients with WM, validate by Sanger sequencing a somatic variant (T→C) in LPL cells was identified at position 38182641 at 3p22.2 predicted an amino acid change (L265P) in MYD88 triggers IRAK-mediated NF-κB signaling 27 of 30 (90%)
Inhibition of MYD88 signaling reduced IκBα, NF- κB p65 phosphorylation, and NF-κB nuclear staining,
Patients 67 patients (42 males, 25 females) diagnosed with WM diagnosis criteria of WM were (1) a lymphoplasmacytic bone marrow (BM) involvement; (2) any level of IgM paraprotein; (3) exclusion of other low-grade lymphomas No familial form of WM was included
High frequency of MYD88 L265P mutation in WM Fifty-three (79%) patients harbor MYD88 L265P mutation (MYD mut ) MYD88 was an acquired mutation as no aberration was identified in the mutational hot spots of MYD88 in T lymphocytes isolated from WM patients (n= 4). not observed any other mutation on exon 5 of MYD88 in our cohort
absent in hairy cell leukemia, MM, mantle cell lymphoma, and CLL MZL (1/16; 6%), follicular lymphoma (1/23, 4%), IgM-MGUS (1/2), 1 case of non-IgM LPL.
Gain of chromosome 3 or acquired UPD, a new mechanisms of alteration of MYD88 locus in WM LOH without copy number changes uniparental disomy (UPD). using SNP array (n =46). found UPD at the MYD88 locus in only 1 patient (2%) homozygous for L265P mutation in tumoral cells not identified mechanisms of loss of MYD88, UPD: 單親二體症 ( 個體一個 染色體對的二套基因僅由父或 母其中一方所提供 )
observed a gain on chromosome 3 at the 3p22 locus (including MYD88 gene) in 7 of 59 (12%) patients, including 2 (5%) patients with MYD88 mutation. gain on chromosome 3 more frequently in the MYD wild group than in the MYD mut group (P 5.006). other cytogenetic aberrations were associated with the gain of chromosome 3 in 6 of 7 patients.
we identified alteration of the MYD88 locus in 91% of patients with WM gain-of-function mutation (79%) or Copy number aberration (12%)
MYD88 mutation is related to NF-kB abnormalities Recent studies have described genomic deletions of 2 potent regulators/inhibitors of the NF-kB pathway in WM, TNFAIP3 (located on 6q23), and deleted in lymphocytic leukemia 7 (located on 13q14) Overall, 63% of WM had at least 1 additional genetic alteration in the NF-kB pathway in our cohort, but no significant difference was observed according to the MYD88 mutation status.
Clinical and biological features of WM with MYD wild 21% MYD wild. MYD88 mutation was not associated with deletion 6q, gain of 4, deletion 11q, deletion 17p, or deletion 13q14 in our study not observe any difference in terms of survival according to the MYD88 mutation status
MYD wild expressed CD27 We found that CD27 (positive in 49% of malignant B cells from WM in our series) was expressed in a significantly lower proportion in the MYD mut group than in the MYD wild group, 30% and 92%, (P=.0001). CD27, a TNF-family member, is expressed on the cell surface of memory B cells from which WM is thought to derive a higher frequency of CD5 positive cases (positive expression in 23% of WM in our series) (P =.043) in MYD wild group
Discussion confirmed a high frequency of MYD88 L265P mutation in this study of 67 patients diagnosed with WM, Treon and colleagues have described MYD88 L265P mutation in 90% of cases in a first series of 46 patients with WM. Few clinical and biological data distinguished MYD wild from MYD mut subgroups in our series
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The high frequency of MYD88mutation in WM highlights the TLR pathway as a new potential pathogenic pathway in WM Our preliminary observations showed that blocking of MYD88 signaling using an inhibitor of MYD88 homodimerization induced cytotoxicity and apoptosis, and reduced cell proliferation, through decreased IRAK4 and STAT3 phosphorylation
MYD88 gene might undergo genetic alterations through other mechanisms, such as UPD, or gain of chromosome 3. additional genetic alterations targeting NF-kB genes such as deletion of TNFAIP3, a negative regulator of NF-kB pathway, were observed.