The purification and properties of a protein kinase and the partial purification of a phosphoprotein phosphatase that inactivate and activate acetyl-CoA carboxylase

the occurrence of a soluble fraction from rat liver that inactivates acetyl-CoA carboxylase was previously reported by this laboratory (1). The purification of this fraction is now reported, and we show that it behaves as a cAMP-independent kinase that inactivates acetyl-CoA carboxylase by phosphorylation. The kinase has a molecular weight of 160,000 and it requires ATP and Mg²⁺ for activity. A partial purification from rat liver cytosol of a Mg²⁺-requiring phosphoprotein phosphatase of high molecular weight (greater than 200,000) which dephosphorylates phosphorylated acetyl-CoA carboxylase with the regeneration of enzyme activity is also reported. The kinase, phosphatase, and acetyl-CoA carboxylase are separable from each other by a combination of ammonium sulfate precipitation, DEAE-cellulose chromatography, and gel filtration.     

Frozen-etched septate junctions

Summary Freeze-etch replicas indicate that septate junctions are formed somewhat differently from the structures proposed on the basis of sectioning studies. The junction appears to be based on ridges on the external surface of the plasma membranes which completely surround the cell sealing off the intercellular space from the external environment of the epithelium. These ridges are reinforced by rows of particles within the two opposing membranes.     

Modulation of natural killer cytotoxicity by muramyl dipeptide and trehalose dimycolate incorporated in squalane droplets

Summary The effect on natural killer (NK) cytotoxicity of splenic cells from BALB/c mice pretreated i. v. with squalane-in-water preparations of muramyl dipeptide (MDP), trehalose dimycolate (TDM), or the combination of MDP-plus-TDM was investigated. MDP or TDM augmented the NK cytotoxicity which peaked 48 h after the pretreatment whereas the combination of MDP and TDM induced an inhibition of the NK activity. Infection with influenza virus, a potent stimulator of NK cells, after the pretreatment with biological response modifiers resulted in a markedly enhanced NK activity on day 2 in MDP and control groups. Mice pretreated with TDM or the combination of MDP and TDM showed only moderate NK activity which peaked on day 3 after influenza infection. The NK activity was susceptible to asialo GM₁ and complement treatment. The cytotoxicity of MDP-plus-TDM cells could be significantly enhanced after treatment with anti-macrophage monoclonal antibody and complement. NK activity induced by MDP or TDM was reduced by mixing MDP-plus-TDM cells. Addition of adherent cell-depleted MDP-plus-TDM suspension to MDP or TDM cells had a NK restorative effect. Splenic cells from mice pretreated 2 days earlier with MDP or TDM, but not MDP-plus-TDM, generated enhanced levels of luminol-dependent chemiluminescence.     

Diabetes mellitus induced by low-dose interleukin-2

 Interleukin-2 (IL-2) is a potent immunomodulator that has been associated with the clinical development of autoimmune disorders. However, diabetes mellitus has not been reported in patients treated with single-agent IL-2. We conducted a clinical trial of a protracted daily schedule of subcutaneously administered low-dose IL-2. A patient with advanced colorectal cancer, treated with 1.5×10⁶ international units of IL-2 daily, developed insulin-requiring diabetes during therapy. Hyperglycemia improved during treatment interruption and recurred with reinstitution of IL-2. The diabetes in this patient developed in the context of T cell and natural killer cell expansion, and the presence of islet cell autoantibodies was documented. We postulate that, in this patient, IL-2 reversed the anergy of autoreactive T cells that had escaped clonal deletion. It is possible that prolonged daily exposure to immunomodulatory doses of IL-2 will result in the development of autoimmune phenomena not observed with other schedules of administration. Received: 15 April 1996 / Accepted: 1 August 1996