The RAS negative feedback gene SPRY4 is a 5q tumor suppressor, and its loss drives AML development.
Major finding: The RAS negative feedback gene SPRY4 is a 5q tumor suppressor, and its loss drives AML development.
Mechanism: Combined suppression of SPRY4, NF1, and p53 activates RAS and accelerates leukemogenesis in mice.
Impact: Deletion of multiple negative regulators may be a broad mechanism to activate RAS signaling in cancer.
Acute myelogenous leukemia (AML) is often characterized by gain-of-function mutations and copy-number amplification of RAS pathway genes that increase downstream MAPK and PI3K signaling to drive oncogenic transformation. Previous studies have shown that oncogenic KrasG12D synergizes with Trp53 loss to promote AML development in mouse models. However, consistent with previous studies, Zhao and colleagues found that expression of KrasG12D alone was not sufficient to induce sustained activation of MAPK and PI3K in premalignant myeloid cells, suggesting that compensatory negative feedback mechanisms may limit RAS-mediated leukemogenesis. In support of this idea, expression of the RAS negative feedback gene Sprouty 4 (Spry4) was increased in myeloid cells expressing mutant KrasG12D, and depletion of Spry4 in KrasG12D-expressing hematopoietic stem and progenitor cells (HSPC) resulted in elevated RAS signaling and accelerated leukemogenesis in mice. Furthermore, SPRY4 deletion was frequently detected in human AML samples harboring deletion of chromosome 5q [del(5q)] that lack gain-of-function RAS mutations, and often occurred in combination with loss of TP53 and other RAS negative feedback genes, including neurofibromin 1 (NF1), suggesting that deletion of multiple negative regulators may facilitate RAS activation in del(5q) AML in the absence of activating mutations. Indeed, concomitant suppression of Spry4 and Nf1 in Trp53-null HSPCs significantly increased the activation of MAPK and PI3K signaling and enhanced the development of myeloid leukemia in transplanted mice, resulting in leukemic cell dissemination and decreased overall survival. These results identify SPRY4 as a tumor suppressor gene in del(5q) AML and support the idea that simultaneous deletion of negative feedback regulators may represent a broad mechanism to drive high levels of RAS signaling in various tumor types.