MPLW515L is a novel somatic activating mutation in myelofibrosis with myeloid metaplasia.
BACKGROUND
The JAK2V617F allele has recently been identified in patients with polycythemia vera (PV), essential thrombocytosis (ET), and myelofibrosis with myeloid metaplasia (MF). Subsequent analysis has shown that constitutive activation of the JAK-STAT signal transduction pathway is an important pathogenetic event in these patients, and that enzymatic inhibition of JAK2V617F may be of therapeutic benefit in this context. However, a significant proportion of patients with ET or MF are JAK2V617F-negative. We hypothesized that activation of the JAK-STAT pathway might also occur as a consequence of activating mutations in certain hematopoietic-specific cytokine receptors, including the erythropoietin receptor (EPOR), the thrombopoietin receptor (MPL), or the granulocyte-colony stimulating factor receptor (GCSFR).


RESULTS
DNA sequence analysis of the exons encoding the transmembrane and juxtamembrane domains of EPOR, MPL, and GCSFR, and comparison with germline DNA derived from buccal swabs, identified a somatic activating mutation in the transmembrane domain of MPL (W515L) in 9% (4/45) of JAKV617F-negative MF. Expression of MPLW515L in 32D, UT7, or Ba/F3 cells conferred cytokine-independent growth and thrombopoietin hypersensitivity, and resulted in constitutive phosphorylation of JAK2, STAT3, STAT5, AKT, and ERK. Furthermore, a small molecule JAK kinase inhibitor inhibited MPLW515L-mediated proliferation and JAK-STAT signaling in vitro. In a murine bone marrow transplant assay, expression of MPLW515L, but not wild-type MPL, resulted in a fully penetrant myeloproliferative disorder characterized by marked thrombocytosis (Plt count 1.9-4.0 x 10(12)/L), marked splenomegaly due to extramedullary hematopoiesis, and increased reticulin fibrosis.


CONCLUSIONS
Activation of JAK-STAT signaling via MPLW515L is an important pathogenetic event in patients with JAK2V617F-negative MF. The bone marrow transplant model of MPLW515L-mediated myeloproliferative disorders (MPD) exhibits certain features of human MF, including extramedullary hematopoiesis, splenomegaly, and megakaryocytic proliferation. Further analysis of positive and negative regulators of the JAK-STAT pathway is warranted in JAK2V617F-negative MPD.
Pikman
Yana
Y
Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
Lee
Benjamin H
BH
Mercher
Thomas
T
McDowell
Elizabeth
E
Ebert
Benjamin L
BL
Gozo
Maricel
M
Cuker
Adam
A
Wernig
Gerlinde
G
Moore
Sandra
S
Galinsky
Ilene
I
DeAngelo
Daniel J
DJ
Clark
Jennifer J
JJ
Lee
Stephanie J
SJ
Golub
Todd R
TR
Wadleigh
Martha
M
Gilliland
D Gary
DG
Levine
Ross L
RL
D019943:Amino Acid Substitution; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000473:pathology; D016026:Bone Marrow Transplantation; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects / Q000473:pathology; D003114:Colony-Forming Units Assay; D016207:Cytokines / Q000494:pharmacology; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D005822:Genetic Vectors; D019337:Hematologic Neoplasms / Q000188:drug therapy / Q000503:physiopathology; D006410:Hematopoiesis / Q000235:genetics / Q000502:physiology; D006801:Humans; D053612:Janus Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D008533:Megakaryocytes / Q000187:drug effects / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D020125:Mutation, Missense; D022423:Myeloid Cells / Q000187:drug effects / Q000473:pathology; D009196:Myeloproliferative Disorders / Q000209:etiology / Q000235:genetics / Q000473:pathology; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D017354:Point Mutation; D055728:Primary Myelofibrosis / Q000235:genetics* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000235:genetics; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000235:genetics / Q000502:physiology; D018121:Receptors, Cytokine / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000009:adverse effects; D050791:STAT Transcription Factors / Q000502:physiology; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013154:Spleen / Q000473:pathology; D013922:Thrombocytosis / Q000209:etiology / Q000235:genetics / Q000473:pathology; D014158:Transcription, Genetic; D039221:mRNA Cleavage and Polyadenylation Factors / Q000235:genetics / Q000502:physiology
D016207:Cytokines; D015514:Oncogene Proteins, Fusion; D047428:Protein Kinase Inhibitors; D018121:Receptors, Cytokine; D011993:Recombinant Fusion Proteins; D050791:STAT Transcription Factors; D039221:mRNA Cleavage and Polyadenylation Factors; C479819:FIP1L1-PDGFRA fusion protein, human; D020796:Receptor, Platelet-Derived Growth Factor alpha; D053612:Janus Kinases