The t(12;21)(p13;q22) chromosomal translocation is the most frequent translocation in childhood B cell precursor-acute lymphoblastic leukemia and results in the expression of an ETV6/RUNX1 fusion protein. The frequency of ETV6/RUNX1 fusions in newborns clearly exceeds the leukemia rate revealing that additional events occur in ETV6/RUNX1-positive cells for leukemic transformation. Hitherto, the mechanisms triggering these second hits remain largely elusive. Thus, we generated a novel ETV6/RUNX1 transgenic mouse model where the expression of the fusion protein is restricted to CD19(+) B cells. These animals harbor regular B cell development and lack gross abnormalities. We established stable pro-B cell lines carrying the ETV6/RUNX1 transgene that allowed us to investigate whether ETV6/RUNX1 itself favors the acquisition of second hits. Remarkably, these pro-B cell lines as well as primary bone marrow cells derived from ETV6/RUNX1 transgenic animals display elevated levels of reactive oxygen species (ROS) as tested with ETV6/RUNX1 transgenic dihydroethidium staining. In line, intracellular phospho-histone H2AX flow cytometry and comet assay revealed increased DNA damage indicating that ETV6/RUNX1 expression enhances ROS. On the basis of our data, we propose the following model: the expression of ETV6/RUNX1 creates a preleukemic clone and leads to increased ROS levels. These elevated ROS favor the accumulation of secondary hits by increasing genetic instability and double-strand breaks, thus allowing preleukemic clones to develop into fully transformed leukemic cells.

We have demonstrated that the signal transducer and activator of transcription 3 (STAT3) protects from cholestatic liver injury. Specific ablation of STAT3 in hepatocytes and cholangiocytes (STAT3∆hc) aggravated liver damage and fibrosis in the Mdr2−/− (multidrug resistance 2) mouse model for cholestatic disease. Upregulation of bile acid biosynthesis genes and downregulation of epidermal growth factor receptor (EGFR) expression were observed in STAT3∆hc Mdr2−/− mice but the functional consequences of these processes in cholestatic liver injury remained unclear. Here, we show normal canalicular architecture and bile flow but increased amounts of bile acids in the bile of STAT3∆hc Mdr2−/− mice. Moreover, STAT3-deficient hepatocytes displayed increased sensitivity to bile acid-induced apoptosis in vitro. Since EGFR signaling has been reported to protect hepatocytes from bile acid-induced apoptosis, we generated mice with hepatocyte/cholangiocyte-specific ablation of EGFR (EGFR∆hc) and crossed them to Mdr2−/− mice. Importantly, deletion of EGFR phenocopied deletion of STAT3 and led to aggravated liver damage, liver fibrosis, and hyperproliferation of K19+ cholangiocytes. Our data demonstrate hepatoprotective functions of the STAT3-EGFR signaling axis in cholestatic liver disease.Key message STAT3 is a negative regulator of bile acid biosynthesis.STAT3 protects from bile acid-induced apoptosis and regulates EGFR expression.EGFR signaling protects from cholestatic liver injury and fibrosis.

A partial cDNA encoding most of the third intracellular loop of the mouse a, d -adrenergic receptor subtype was amplified from hippocampus by reverse transcription-polymerase chain reaction (RT-PCR) using degenerate oligodeoxynucleotide primers . This DNA fragment was used as a probe to isolate an a, d -adrenergic receptor cDNA from a mouse brain cDNA library . The deduced amino acid sequence encodes a potential protein of 562 amino acids, and northern hybridization of poly(A)+ RNA isolated from mouse brain detected a single 3 .0-kb transcript . Partial cDNA fragments of the alband a, a -adrenergic receptor subtypes were also amplified from mouse brain and sequenced . Analysis of the mRNA expression by RT-PCR indicated that the a,-adrenergic receptors are widely distributed in mouse tissues . The a,d subtype is expressed in brain areas such as hippocampus, striatum, and brainstem and also in many extracerebral tissues, such as lung, liver, heart, kidney, and spleen . The a,a subtype is also expressed in many tissues, whereas the alb subtype has a more restricted expression, with high levels in striatum, brainstem, and diencephalus . Key Words : a,d -Adrenergic receptor-Mouse-cDNA cloning-Tissue distribution -a,-Adrenergic receptor subtypes . J. Neurochem . 65, 2387Neurochem . 65, -2392Neurochem . 65, (1995 .The adrenergic receptors are members of a large family of membrane proteins that are coupled to guanine nucleotide-binding proteins (G proteins) . They are currently divided into three types (a,, a2 , and ß), each having several receptor members (Lomasney et al., 1991a ;Bylund, 1992) . Radioligand binding data with the a,-adrenergic receptor agonists oxymetazoline and methoxamine and the antagonists WB4101 and phentolamine indicated the existence of two a,-adrenergic receptor subtypes in rat cerebral cortex, which were named a1A and a,B (Battaglia et al., 1983 ; Morrow and Creese, 1986;Han et al., 1987) .Several cDNAs and genes encoding a t-adrenergic receptor subtypes from various sources, and initially named a]A/alD, a,B , and a lc , have been isolated by