[Mechanisms of pharmacokinetic drug interactions. 4: Mechanisms of interaction during biotransformation].
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We have previously shown (Smith et al., 1994) that antibodies raised against the growth arrest and DNA damage inducible protein Gadd45 co-precipitate proliferating cell nuclear antigen (PCNA), a protein involved in DNA replication and repair. Here we demonstrate that Gadd45 can directly bind to PCNA using a Far-western blotting approach. In this assay, a Gadd45 bacterial expression vector was modified to allow synthesis of purified 32P-labeled Gadd45 fusion protein. This protein was used to detect filter bound PCNA protein, while filter bound Gadd45 protein could also be detected by free PCNA molecules. Using recombinant proteins in conjunction with immunoprecipitation and immunoblotting, we show that Gadd45 competes with p21 for binding to PCNA and conversely, p21 blocks the ability of Gadd45 to bind PCNA. In addition, p21 appears to disrupt PCNA trimers whereas Gadd45 has a lesser effect. PCNA trimer disruption was also observed in UV-irradiated cells but not in repair-defective xeroderma pigmentosum group A (XP-A) cells.
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Biomaterial-associated infection results in increased morbidity and mortality, and may occur because of nonproductive premature activation of neutrophils resulting in impaired phagocyte function at the biomaterial surface in the event of bacterial challenge. To further explore the effects of this premature activation, we evaluated the supernatants of biomaterial associated neutrophils to determine whether soluble mediators were released, and the likely role of these mediators. We show that these supernatants contain a chemoattractant and thereby induce chemotaxis by fresh neutrophils. No evidence of enhanced oxidative free radical production by either unstimulated neutrophils or a primed response to other mediators occurs when neutrophils were incubated with these supernatants. We also examined the effect of adding fresh neutrophils to a biomaterial surface containing a previous inoculum of neutrophils, and observed that the fresh cells did not become stimulated to release reactive oxygen intermediates (ROI) and also exhibited impaired killing of staphylococci. These studies suggest that not only does the biomaterial surface activate the initial wave of neutrophils but that subsequent waves of neutrophils exhibit an impaired host-defense function. These results are consistent with the known impairment of host defense in the presence of biomaterials, and provide evidence for a long-term down-regulation of neutrophil function at biomaterial surfaces.
Several lines of evidence indicate that the adapter molecule p130CAS (crk-associated substrate (CAS)) is required for src-mediated cellular transformation. CAS has been shown to be heavily tyrosine-phosphorylated in src-transformed cells, and genetic variants of src that are deficient in CAS binding are also unable to mediate cellular transformation. In this report, we investigated whether CAS phosphorylation and/or its association with src are required elements of the transformation process. Expression of the carboxy-terminal src binding domain of CAS in Rat 1 fibroblasts expressing a temperature-sensitive allele of v-src inhibited the formation of src-CAS complexes and also inhibited tyrosine phosphorylation of CAS. However, expression of this protein had no effect on morphological transformation, src-mediated actin rearrangements, or anchorage-independent growth of these cells when grown at the src-permissive temperature. Thus, the ability of activated src to mediate cellular transformation is either largely independent of endogenous CAS phosphorylation and/or its association with CAS or, alternatively, the carboxy-terminus of CAS may substitute for endogenous CAS in the process of src-mediated transformation.
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Prostaglandin E2 (PGE2), at concentration larger than or equal to 5 x 10(4) ng/ml, induced discocyte leads to echinocyte transformation of saline-suspended hemoglobin (Hb) AA and SS erythrocytes. This erythrocyte transformation is concentration-dependent and is reversible at room temperature after 90-120 min. The Hb SS erythrocytes treated with PGE2 did not exhibit accelerated sickling or increased formation of sickled echinocytes. Erythrocytes suspended in autologous plasma treated with PGE2, 2 X 10(6) ng/ml, did not exhibit echinocytic transformation probably because of drug binding to the plasma proteins. Other in vitro studies showed that PGE2 of concentrations of 10-500 ng/ml had no adverse effects on intact, plasma-suspended Hb SS erythrocytes. These Hb SS erythrocytes were examined for changes in morphology, potassium and calcium flux, and blood viscosity under oxygenated and hypoxic conditions.
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