Image by Lance Liotta
AML cells
New research suggests SHARP1 may be a therapeutic target in MLL-AF6 acute myeloid leukemia (AML).
Researchers found that SHARP1, a circadian clock transcription factor, is overexpressed in MLL-AF6 AML.
In mouse models, suppression of SHARP1 induced apoptosis in leukemic cells, while deletion of SHARP1 delayed AML development and weakened leukemia-initiating potential.
“We found that MLL-AF6 binds with SHARP1, leading to an increase in the level of SHARP1,” explained study author Dan Tenen, MD, of the Cancer Science Institute of Singapore.
“The increase of SHARP1 levels has the 2-fold effect of initiating leukemia development, as well as maintaining the growth of leukemic cells. [O]ur study also revealed that SHARP1 could act upon other target genes of MLL-AF6 to aggravate the progression of AML, but, by removing or reducing the level of SHARP1, the growth of leukemic cells could be stopped.”
Dr Tenen and his colleagues reported these findings in Nature Communications.
The researchers found that SHARP1 was overexpressed in MLL-AF6 AML, but its expression was decreased in most other subtypes of AML analyzed as well as in normal bone marrow CD34+ cells.
Experiments in AML cell lines revealed that SHARP1 expression is regulated by MLL-AF6/DOT1L. The researchers said MLL-AF6 and MEN1/LEDGF directly bind to the SHARP1 gene locus to positively regulate SHARP1 expression through DOT1L activity.
Dr Tenen and his colleagues performed knockdown experiments in mice and found that SHARP1 plays a “critical” role in maintaining clonogenic growth and preventing apoptosis in MLL-AF6 AML cells.
The team also assessed the effects of SHARP1 deletion in mouse models of MLL-AF6 AML.
SHARP1 knockout mice had superior survival compared to wild-type mice. In addition, the knockout mice exhibited signs of less aggressive disease—fewer AML cells, lower white blood cell counts, and higher red blood cell counts.
The researchers also found that SHARP1 deletion reduced MLL-AF6 leukemia-initiating ability but did not affect normal hematopoiesis.
Finally, the team discovered that SHARP1 cooperates with MLL-AF6 to regulate target genes in MLL-AF6 AML cells.