KRASG12V enhances proliferation and initiates myelomonocytic differentiation in human stem/progenitor cells via intrinsic and extrinsic pathways

Abstract

In human hematopoietic malignancies, RAS mutations are frequently observed. Yet, little is known about signal transduction pathways that mediate KRAS-induced phenotypes in human CD34+ stem/progenitor cells. When cultured on bone marrow stroma, we observed that KRASG12V-transduced cord blood (CB) CD34+ cells displayed a strong proliferative advantage over control cells, which coincided with increased early cobblestone (CAFC) formation and induction of myelomonocytic differentiation. However, the KRASG12V-induced proliferative advantage was transient. By week three no progenitors remained in KRASG12V-transduced cultures and cells were all terminally differentiated into monocytes/macrophages. In line with these results, LTC-IC frequencies were strongly reduced. Both the ERK and p38 MAPK pathways, but not JNK, were activated by KRASG12V and we observed that proliferation and CAFC formation were mediated via ERK, while differentiation was predominantly mediated via p38. Interestingly, we observed that KRASG12V-induced proliferation and CAFC formation, but not differentiation, were largely mediated via secreted factors, since these phenotypes could be recapitulated by treating non-transduced cells with conditioned medium harvested from KRASG12V-transduced cultures. Multiplex cytokine arrays and genome-wide gene expression profiling were performed to gain further insight into the mechanisms by which oncogenic KRASG12V can contribute to the process of leukemic transformation. Thus, angiopoietin-like 6 (ANGPTL6) was identified as an important factor in the KRASG12V secretome that enhanced proliferation of human CB CD34 + cells. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.