Role of p21 RAS in p210 bcr-abl transformation of murine myeloid cells

Abstract

The p21 RAS product has been implicated as part of the downstream signaling of certain nonreceptor tyrosine kinase oncogenes and several growth factor receptor-ligand interactions. We have reported that the chronic myelogenous leukemia oncogene p210 bcr-abl transforms a growth- factor-dependent myeloid cell line NFS/N1.H7 to interleukin-3 (IL-3) independence. In these p210 bcr-abl-transformed cells (H7 bcr-abl.A54) and in two other murine myeloid cell lines transformed to IL-3 independence by p210 bcr-abl, endogenous p21 RAS is activated as determined by an elevated ratio of associated guanosine triphosphate (GTP)/guanosine diphosphate (GDP), assayed by thin-layer chromatography of the nucleotides eluted from p21 RAS after immunoprecipitation with the Y13–259 antibody. Treatment of p210 bcr-abl-transformed cells with a specific tyrosine kinase inhibitor herbimycin A resulted in diminished tyrosine phosphorylation of p210 bcr-abl and associated proteins, without major reduction in expression of the p210 bcr-abl protein itself. Inhibition of p210 bcr-abl-dependent tyrosine phosphorylation resulted in a reduction of active p21RAS-GTP complexes in the transformed cells, in diminished expression of the nuclear early response genes c-jun and c-fos, and in lower cellular proliferation rate. To further implicate p21 RAS in these functional events downstream of p210 bcr-abl tyrosine phosphorylation, we targeted G- protein function directly by limiting the availability of GTP with the inosine monophosphate dehydrogenase inhibitor, tiazofurin (TR). In p210 bcr-abl-transformed cells treated for 4 hours with TR, in which the levels of GTP were reduced by 50%, but GDP, guanosine monophosphate, and adenosine triphosphate (ATP) were unaffected, p210 bcr-abl tyrosine phosphorylation was at control levels. However, expression of c-fos and c-jun nuclear proto-oncogenes were strongly inhibited and p21 RAS activity was downregulated. These findings show that p210 bcr-abl transduces proliferative signals, in part, through downstream activation of p21 RAS. Furthermore, p21 RAS activity is linked to pathways that regulate c-jun and c-fos expression.

Chronic myeloid leukemia: 2018 update on diagnosis, therapy and monitoring

“…This results in expression of an oncoprotein termed BCR‐ABL1 . BCR‐ABL1 is a constitutively active tyrosine kinase that promotes growth and replication through downstream signaling pathways such as RAS, RAF, JUN kinase, MYC, and STAT . This influences leukemogenesis by creating a cytokine‐independent cell cycle with aberrant apoptotic signals in response to cytokine withdrawal.…”

Chronic myeloid leukemia: 2012 update on diagnosis, monitoring, and management

“…Central to the pathogenesis of CML is the fusion of the Abelson murine leukemia (ABL) gene on chromosome 9 with the breakpoint cluster region (BCR) gene on chromosome 22, which results in expression of an oncoprotein, termed BCR‐ABL [2]. BCR‐ABL is a constitutively active tyrosine kinase that promotes growth and replication through downstream pathways such as RAS, RAF, JUN kinase, MYC and STAT [3–9]. This influences leukemogenesis by creating a cytokine‐independent cell cycle with aberrant apoptotic signals in response to cytokine withdrawal.…”

Guanine nucleotide exchange factors: Activators of the Ras superfamily of proteins

“…The role of Ras activation in BCR/Abl function is supported by several lines of evidence. First, Ras-GTP levels are elevated in myeloid cells expressing BCR/Ab1 (74). Second, mutation of the Grb2 binding site in BCR/Abl impairs BCR/Abl-induced transformation of lymphoid cells (75).…”