Retroviral oncogenes encode nuclear regulators of gene expression or signal transduction molecules, such as protein kinases, which stimulate the activity of cellular transcription factors. Here we describe the cloning of NF‐M, a myeloid‐specific transcription factor related to C/EBP beta, which is a target of activated protein kinases. NF‐M stimulates the expression of the gene encoding cMGF, a myeloid cell‐specific growth factor, creating an autocrine growth loop crucial to oncogene transformation of myeloid cells. The NF‐M protein bound directly to the cMGF gene promoter and activated its transcription, even in erythroid cells where the promoter is usually inactive. In addition, a truncated, dominant‐negative form of NF‐M inhibited cMGF expression in macrophages, indicating that NF‐M is required for the normal activation of the gene. When multipotent hematopoietic progenitor cells were stimulated to differentiate, NF‐M expression was induced at a very early stage, suggesting that the transcription factor plays a role in lineage commitment. The stimulation of transformed myelomonocytic cells or of normal peripheral blood macrophages with kinases or LPS or TPA respectively, led to the rapid redistribution of NF‐M protein from the cell bodies to the nucleus, consistent with the notion that NF‐M was directly affected by such treatments. Our data indicate that NF‐M plays a key role in myelomonocytic differentiation, in signal transduction during macrophage activation and in the development of myelogenous leukemia.

The nuclear oncogenes v‐myc or v‐myb specifically transform avian myeloid cells. In both cases, the transformed cells remain dependent on chicken myelomonocytic growth factor (cMGF). This factor dependence can be relieved by expression of kinase‐type oncogenes such as v‐mil or v‐erbB, leading to expression of cMGF and autocrine growth stimulation. In erythroid cells the same kinase‐type oncogenes cause transformation but do not induce cMGF expression. Here we investigated the molecular mechanisms of the observed lineage specific oncogene collaboration. We found that kinase‐type oncogenes and TPA activate the cMGF promoter via AP‐1 like transcription factors. The activation of the cMGF promoter is, however, strictly dependent on the binding of nuclear proteins to both halves of an inverted repeat adjacent to the AP‐1 binding site. These proteins are related to C/EBP. They are expressed exclusively in myeloid cells and were therefore termed NF‐M. Our results indicate that the lineage specific cooperation of kinase type oncogenes with v‐myb or v‐myc in leukemia formation is based on the concerted action of AP‐1 and NF‐M on the cMGF promoter.

Background Considerable evidence suggests that CaMKII overactivity plays a crucial role in the pathophysiology of heart failure (HF), a condition characterized by excessive β-adrenoceptor (β-AR) stimulation. Recent studies indicate a significant crosstalk between β-AR signaling and CaMKII activation presenting CaMKII as a possible downstream mediator of detrimental β-AR signaling in HF. In this study we investigated the effect of chronic β-AR blocker treatment on CaMKII activity in human and experimental HF. Methods and Results Immunoblot analysis of myocardium from end stage HF patients (n=12) and non-HF subjects undergoing cardiac surgery (n=12) treated with β-AR blockers revealed no difference in CaMKII activity when compared to non-β-AR-blocker-treated patients. CaMKII activity was judged by analysis of CaMKII expression, autophosphorylation and oxidation and by investigating the phosphorylation status of CaMKII downstream targets. To further evaluate these findings, CaMKIIδC transgenic mice were treated with the β1-AR blocker metoprolol (270 mg/kg*d). Metoprolol significantly reduced transgene-associated mortality (n≥29, p<0.001), attenuated the development of cardiac hypertrophy (−14±6% heart weight/tibia length, p<0.05) and strongly reduced ventricular arrhythmias (−70±22% PVCs, p<0.05). On a molecular level, metoprolol expectedly decreased PKA dependent phospholamban (PLN) and ryanodine receptor 2 (RyR2) phosphorylation (−42±9% for P-PLN-S16 and −22±7% for P-RyR2-S2808, p<0.05). However, this was neither paralleled by a reduction in CaMKII autophosphorylation, oxidation and substrate binding nor a change in the phosphorylation of CaMKII downstream target proteins (n≥11). The lack of CaMKII modulation by β-AR blocker treatment was confirmed in healthy wildtype mice receiving metoprolol. Conclusions Chronic β-AR blocker therapy in patients and in a mouse model of CaMKII-induced HF is not associated with a change in CaMKII activity. Thus, our data suggests that the molecular effects of β-AR blockers are not based on a modulation of CaMKII. Directly targeting CaMKII may therefore further improve HF therapy in addition to β-AR blockade.