MSPCs with mutant PTPN11
(red) and monocytes (green).
Image courtesy of
Dong et al, Nature 2016
New research published in Nature has shown how certain mutations drive the development of myeloproliferative neoplasms (MPNs) and leukemia.
Investigators discovered that PTPN11 activating mutations promote the development and progression of MPNs through “profound detrimental effects” on hematopoietic stem cells (HSCs).
The team also identified a potential method of treating MPNs in patients with Noonan syndrome.
Noonan syndrome can be caused by mutations in several genes, but the most common is PTPN11. Children with Noonan syndrome are known to have an increased risk of developing MPNs/leukemia.
Previous research had established that mutations in PTPN11 have a conventional cell-autonomous effect on HSC growth.
In the current study, investigators showed that PTPN11 mutations also affect mesenchymal stem/progenitor cells (MSPCs) and osteoprogenitors.
The mutations cause over-production of the CC chemokine CCL3, which attracts monocytes into the HSCs’ niches. The monocytes make inflammatory molecules that stimulate the HSCs to differentiate and proliferate, leading to MPNs and leukemia.
“We have identified CCL3 as a potential therapeutic target for controlling leukemic progression in Noonan syndrome and for improving stem cell transplantation therapy in Noonan syndrome-associated leukemias,” said study author Cheng-Kui Qu, MD, PhD, of Emory University School of Medicine in Atlanta, Georgia.
Dr Qu and his colleagues began this research intending to investigate the effects of PTPN11 mutations in the nervous system. The team developed genetically engineered mice that had altered PTPN11 in neural cells.
The mice all developed a condition resembling an MPN at an early age. It turned out that the mice had changes in the PTPN11 gene in their MSPCs and osteoprogenitors (in addition to their neural cells) but not in their HSCs.
The investigators found the MPN in these PTPN11-mutant mice can be treated in the short-term by HSC transplant, but the condition comes back within months.
However, drugs counteracting CCL3 successfully reversed MPN phenotypes. One of the drugs is the CCR5 antagonist maraviroc, which is approved in the US to combat HIV infection, and another is the CCR1 antagonist BX471.
The investigators noted that other Noonan syndrome mutations, in genes besides PTPN11, need to be assessed for their effects on MPN/leukemia formation.
