Identification, molecular cloning, and characterization of dual leucine zipper bearing kinase. A novel serine/threonine protein kinase that defines a second subfamily of mixed lineage kinases

Molecular cloning using a degenerate oligonucleotide-based polymerase chain reaction was undertaken to test the possibility that novel, developmentally regulated protein kinases are expressed in the embryonic mouse kidney. Several receptor tyrosine kinase and serine/threonine kinase cDNA clones were identified. One of these, designated DLK, represented a novel gene product whose 3.6-kilobase transcript was expressed in a tissue-specific and developmentally regulated fashion. Several clones encoding the entire open reading frame were isolated and sequenced. The identified open reading frame encodes an 888-amino acid polypeptide that defines a new subfamily within the mixed lineage protein kinase family. Sequence analysis revealed: 1) a kinase catalytic domain most characteristic of serine/threonine kinases but hybrid between members of the family of microtubule-associated protein kinase kinase kinases and the fibroblast growth factor receptor family; 2) two putative alpha-helical leucine zipper motifs separated by a 25-amino acid charged intermediate segment but lacking an NH2-terminal basic domain; and 3) COOH-terminal and NH2-terminal proline-rich domains suggestive of src homology 3 (SH3) domain binding regions. Rabbit polyclonal immune sera generated against a carboxyl-terminal bacterial fusion protein recognized a protein with an apparent molecular mass of 130 kDa in COS 7 cells that were transiently transfected with a full-length DLK cDNA expression vector. Moreover, COS 7 cells transiently transfected with an epitope-tagged DLK expression vector expressed protein with an apparent molecular mass of 130 kDa that became autophosphorylated on serine and threonine in an in vitro kinase assay.

BDNF supports mammalian chemoafferent neurons in vitro and following peripheral target removal in vivo

Chemoreceptor neurons innervating the rat carotid body were used as a model system to define target regulation of visceral sensory development in fetal and newborn animals. In vitro, chemoafferents were selectively supported by coculture with the carotid body or by treatment with trkB ligands [brain-derived neurotrophic factor (BDNF) and neurotrophin-4], whereas nerve growth factor and neurotrophin 3 had no effect. In vivo, chemoafferent neurons died following carotid body removal at birth, indicating a predominant role of peripheral, rather than central, targets in mediating survival at this stage. However, in the absence of target tissues, a large proportion of carotid body afferents could be rescued by implants containing BDNF. Moreover, BDNF mRNA was detected in the newborn carotid body by reverse transcriptase polymerase chain reaction. These data provide the first demonstration that BDNF can substitute for peripheral target support of sensory neuron survival in vivo and indicate that trkB ligands may be particularly important for development of visceral afferents involved in cardiorespiratory control.

Temporal effects of prolactin on casein kinase activity, casein synthesis and casein mRNA accumulation in mouse mammary gland explants

Studies were carried out to investigate the mechanism by which prolactin stimulates casein synthesis in cultured mouse mammary tissues. The onset of the prolactin stimulation of casein synthesis occurs 8-10 hours after prolactin addition to cultured tissues; a maximum effect is evoked by 16 hours. A similar time-course of response to prolactin was observed when the tissue accumulation of the mRNA for beta-casein was determined. At 16 hours, however, prolactin had no effect on tissue-specific casein kinase activity which is associated with the Golgi apparatus. These studies suggest that the tissue content of casein mRNA is causally related to the onset of the prolactin stimulation of casein synthesis in cultured mouse tissues. In contrast, the activity of the kinase that catalyzes the phosphorylation of the caseins is not altered by prolactin and thus apparently is not a contributing factor to the early prolactin effect on casein synthesis.

A proper transmembrane Ca2+ gradient is essential for the stimulation of adenylate cyclase activity by stimulatory GTP-binding protein

Stimulatory GTP-binding Protein (Gs) and adenylate cyclase prepared from bovine brain cortices were co-reconstituted into asolectin vesicles with or without 1000-fold transmembrane Ca2+ gradient. The results showed that both basal activity and Gs-stimulated activity of adenylate cyclase were highest in proteoliposomes with a transmembrane Ca2+ gradient similar to physiological condition (1 microM Ca2+ outside and 1 mM Ca2+ inside) and lowest when the transmembrane Ca2+ gradient was in the inverse direction. Such a difference could be diminished following dissipation of the transmembrane Ca2+ gradient by A23187. Comparable conformational changes of Gs in proteoliposomes were also observed when Gs was labeled with the fluorescence probe, acrylodan. These results may indicate that a proper transmembrane Ca2+ gradient is essential not only for higher adenylate cyclase activity but also for its stimulation by Gs.

Prolactin stimulation of protein kinase C in isolated mouse mammary gland nuclei

Prolactin (PRL) was found to stimulate protein kinase C (PKC) activity in a transient fashion in isolated nuclei derived from the mammary glands of 12-14 day pregnant mice. PKC activation was time and dose dependent and was blocked by staurosporine. With 10 ng/ml PRL a maximum stimulation of PKC occurred at 3 min, whereas with 50 ng/ml the effect was maximal at 2 min. After 5 min, the effect of PRL on PKC activity was no longer detected. Specificity of the PRL effect on PKC was established by showing that bovine growth hormone and insulin at 10 ng/ml had no effect on PKC activity. Multiple proteins in the nuclear preparations were shown to be phosphorylated by the addition of PKC derived from rat brain tissue. These studies have important implications regarding the possible direct effects of prolactin in the nucleus of mammary cells.

Effects of the protein phosphatase inhibitor okadaic acid on the actions of prolactin in cultured mouse mammary gland explants

The effects of okadaic acid on ornithine decarboxylase (ODC) activity and milk product formation were studied in cultured mammary tissues derived from midpregnant mice. Okadaic acid stimulated ODC activity as well as the synthesis of lactose, lipids, and casein-rich phosphoproteins. When tested together, okadaic acid and prolactin evoked a nonadditive stimulation of lactose synthesis. In addition, the time-courses for the okadaic acid and prolactin effects on lactose synthesis were the same. In contrast to the effects of okadaic acid and prolactin on lactose synthesis, these agents generated additive stimulatory effects on ODC activity and the synthesis of lipids and casein-rich phosphoproteins. Since okadaic acid is known to inhibit protein phosphatases-1 and 2A, we conclude that the substrate(s) of these phosphatases are involved in the signal transduction pathway by which prolactin expresses its effect on lactose synthesis in mammary tissues. Whether these substrates are also involved in other actions of prolactin in mammary tissues remains to be established.

Possible role of tyrosine kinases in the prolactin stimulation of cell division in Nb2 node lymphoma cells

Orthovanadate and genistein were employed to determine the possible role of tyrosine kinase in the prolactin stimulation of cell division in Nb2 node lymphoma cells. Orthovanadate (0.1-0.25 microM), an inhibitor of specific phosphatases, was found to stimulate cell division as well as potentiate the mitogenic effect of prolactin on Nb2 cells when prolactin was employed at a less than maximum stimulatory concentration. Genistein, an inhibitor of tyrosine kinase, was found to inhibit the prolactin stimulation of cell division. Since prolactin was shown in earlier studies to stimulate the phosphorylation of tyrosyl residues in specific Nb2 cell proteins, these results suggest that the signal transduction pathway for the prolactin stimulation of cell division in the Nb2 node lymphoma cells likely involves the participation of tyrosine kinase(s).

Non-neuronal cells inhibit catecholaminergic differentiation of primary sensory neurons: role of leukemia inhibitory factor

Although some sensory ganglion cells in mature animals are catecholaminergic, most mammalian sensory neurons that express the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) do so only transiently during early gangliogenesis in vivo. The lack of TH expression at later stages appears to be due to modulation of this catecholaminergic potential. A previous study showed that the phenotype reappears, for example, when E16.5 and older sensory ganglia are dissociated in culture into single cells, suggesting that extracellular influences can modulate TH expression. Moreover, TH expression in dissociate cultures is cell-density dependent, as a four-fold increase in plating density led to a 30% decrease in the percentage of TH neurons. The present study demonstrates that inhibition of TH expression in high density cultures is mediated by ganglionic non-neuronal cells (NNC), as removal of NNC abolished density-dependent inhibition. Moreover, plating E16.5 trigeminal neurons at low density on top of NNC monolayers resulted in an 85% decrease in the percentage of TH neurons. Treatment of cultures with non-neuronal cell conditioned medium (NNC-CM) reproduced the effect of coculture with NNC, suggesting that diffusible factors from NNC were involved in the inhibition of TH. The inhibitory effect of NNC-CM was mimicked by treatment of dissociate cultures with ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF). However, immunoprecipitation of NNC-CM with antibodies against LIF or CNTF showed that only anti-LIF antibodies were able partially to remove the TH inhibitory activity of NNC-CM. Therefore, LIF is one, but not the only, factor mediating NNC inhibition of TH expression in cultured sensory neurons. In summary, these data indicate that ganglionic NNC can regulate sensory transmitter phenotype in culture by inhibiting expression of specific molecular traits. The finding that LIF can partially account for the inhibitory effect of ganglionic NNC on TH expression suggests a novel role for this cytokine in regulating differentiation of catecholaminergic properties in sensory neurons.

[Effect of endothelin and endothelin-antiserum on ischemia/reperfusion injury in isolated rat hearts]

Reperfusion of isolated perfused rat hearts with 10(-9) mol/L endothelin (ET) significantly exacerbated the ischemia/reperfusion injury(I/R), in contrast, reperfusion with specific ET-antiserum dramatically alleviated myocardial I/R injury. The results suggest that ET may be an important factor, which contributes to the pathogenesis of myocardial I/R injury.

[Effect of endothelin on isolated myocytes from rat heart]

The mechanism of endothelin (ET) action on isolated myocytes of rat heart was investigated. Administration of 10(-9)-10(-7) mol/L ET caused dose-dependently severe contracture of myocytes, increase in cytosolic lactate dehydrogenase leakage and increase of cellular total calcium. ET also enhanced 45Ca2+ influx in myocytes, that could be antagonized by calcium channel blocker verapamil. Incubation of Fura-2 -preloaded myocytes with ET would induce a significant increase of cytosolic free Ca2+, and this effect of ET could also be partly antagonized by verapamil. These results suggest that ET enhances Ca2+ influx in myocytes mainly through voltage-dependent calcium channel, by which ET exerts its biological action.

Effect of a tyrosine kinase inhibitor, genistein, on the actions of prolactin in cultured mouse mammary tissues

Genistein, an inhibitor of tyrosine kinase, was used to determine the possible role of tyrosine kinase in the prolactin (PRL) stimulation of milk product formation and ornithine decarboxylase (ODC) activation in cultured mouse mammary gland tissue. Genistein (10-200 microM) inhibited in a dose-response fashion the PRL stimulation of casein, lipid and lactose synthesis as well as ODC activation. Genistein, however, did not inhibit the phospholipase C, phorbol myristate acetate or cAMP effects on ODC activation. These results suggest the possible involvement of tyrosine kinase in the mechanism by which PRL expresses its effects in mammary gland tissues.

[Effect of endothelin on rat mesenteric microvessels]

By video microscope, it was observed that endothelin (ET) caused constriction of the mesenteric microvessels of pentobarbital-anesthetized Wistar rats in a dose-dependent manner. With the consequence of causing a decrease of rate of blood flow and even some microcirculation disorder, the action was long lasting. The constrictive effect of ET on microvessel was much stronger than norepinephrine. The results suggest that ET is a potent vasoconstrictor for microvessel and may play an important role in causing microcirculatory disorder.

The variety of sterility and gradual progression to fertility in hybrids of the horse and donkey

Generally speaking, the majority of F1 hybrids between the horse and donkey are sterile and do conform to the hypothesis of gametogenic breakdown. The results of our own research, nevertheless, lead us to conclude that there is variability in degree of sterility and fertility for both F1 and B1 individuals, with a gradual advance from sterility to fertility being seen. This is the subject we will discuss from the point of view of oestrus, ovulation, mating, pregnancy, spermatogenesis, endocrine activity, isozymes and karyotypic analysis in this paper.