Expression and reconstitution of NF-kappaB from insect cells using a baculovirus vector

Enhancement of nuclear factor-kappa B acetylation by coactivator p300 and HIV-1 Tat proteins

Nuclear factor (NF)-kappaB transcription factors are involved in the control of a large number of normal cellular and organismal processes, such as immune and inflammatory responses, developmental processes, cellular growth, and apoptosis. Transcription of the human immunodeficiency virus type 1 (HIV-1) genome depends on the intracellular environment where the integrate viral DNA is regulated by a complex interplay among viral regulatory proteins, such as Tat, and host cellular transcription factors, such as NF-kappaB, interacting with the viral long terminal repeat region. CBP (CREB-binding protein) and p300, containing an intrinsic histone acetyltransferase (HAT) activity, have emerged as coactivators for various DNA-binding transcription factors. Here, we show that the p50 subunit as well as the p50/p65 of NF-kappaB, and not other factors such as SP1, TFIIB, polymerase II, TFIIA, or p65, can be acetylated by CBP/p300 HAT domain. Acetylation of p50 was completely dependent on the presence of both HAT domain and Tat proteins, implying that Tat influences the transcription machinery by aiding CBP/p300 to acquire new partners and increase its functional repertoire. Three lysines, Lys-431, Lys-440, and Lys-441 in p50 were all acetylated in vitro, and a sequence similarity among p50, p53, Tat, and activin receptor type I on these particular lysines was observed. All proteins have been shown to be acetylated by the CBP/p300 HAT domain. Acetylated p50 increases its DNA binding properties, as evident by streptavidin/biotin pull-down assays when using labeled NF-kappaB oligonucleotides. Increased DNA binding on HIV-1 long terminal repeat coincided with increases in the rate of transcription. Therefore, we propose that acetylation of the DNA binding domain of NF-kappaB aids in nuclear translocation and enhanced transcription and also suggest that the substrate specificity of CBP/p300 can be altered by small peptide molecules, such as HIV-encoded Tat.

Functional characterization of a purified, recombinant NF-kappaB/IkappaB complex

The NF-kappaB signal transduction pathway involves the interaction of several NF-kappaB and IkappaB family members that are activated by a diverse range of extracellular signals and that stimulate many different cellular responses. The biochemical regulation of this cascade can be studied by establishing a cell-free system using purified proteins. As a first step toward establishing an in vitro model incorporating multiple combinations of NF-kappaB and IkappaB proteins, we produced purified human p65 (RelA) and human IkappaBalpha proteins and tested their functionality. Full-length RelA and IkappaBalpha proteins were overproduced by coinfection of TN5-JE cells with two recombinant baculoviruses. RelA and IkappaBalpha formed a stable complex that could be purified to >95% homogeneity. Protein-protein interactions, protein-DNA binding, and protein phosphorylation were similar to the native proteins.

Nuclear Factor-κB Mediates TNF-α Inhibitory Effect on α2(I) Collagen (COL1A2) Gene Transcription in Human Dermal Fibroblasts

Among its plethora of activities as an inflammatory mediator, TNF-α has potent regulatory control on extracellular matrix production and degradation. Earlier studies have documented that TNF-α inhibits type I collagen gene (COL1A2) expression at the transcriptional level, but the characterization of the transcription factors involved has been elusive. In the present study, using transient cell transfection of human dermal fibroblasts with a battery of 5′ end deletion/chloramphenicol acetyltransferase (CAT) reporter gene constructs, we have characterized the TNF-α response element of the COL1A2 promoter. The TNF-α response element was attributed to a specific region that comprises noncanonical activator protein-1 (AP-1) (CGAGTCA) and NF-κB (AGAGTTTCCC) binding sites. TNF-α effect was eliminated by a 2-bp substitution mutation in the NF-κB1 binding half site of the NF-κB cis element. Electrophoretic mobility shift assays (EMSA) showed that recombinant human NF-κB heterodimers as well as NF-κB1 and RelA homodimers, but not AP-1, were capable of binding this element. Further, EMSA with human fibroblast nuclear extracts demonstrated enhanced binding of a single, specific complex within 5 min of TNF-α stimulation, which reached a plateau by 1 h and was not affected by preincubation of cells with cycloheximide. Gel supershift assays identified the complex as the NF-κB (p50/p65) heterodimer, whereas Abs to nuclear factor of activated T cells (NF-AT) and Jun family members failed to recognize the complex. These data suggest that in fibroblasts TNF-α activates and initiates the nuclear translocation of NF-κB that binds a divergent NF-κB element and plays a critical role in the observed inhibition of α2(I) collagen gene transcription.

Expression, purification, and bioassay of human stanniocalcin from baculovirus-infected insect cells and recombinant CHO cells

Stanniocalcin is a calcium- and phosphate-regulating glycoprotein hormone that was first described in fish where it functions in preventing hypercalcemia. Human cDNA clones encoding the homolog of stanniocalcin have been recently isolated. In this study, the full-length cDNA coding for human stanniocalcin (hSTC) was cloned into both baculovirus and CHO expression vectors. Recombinant hSTC was then produced efficiently from both baculovirus-infected insect cells and CHO cells in large-scale bioreactors. Purification protocols were developed and used to purify recombinant hSTC from both sources in four chromatography steps. The hSTCs from both expression systems were secreted as glycosylated proteins and as disulfide-linked homodimers. The results from glycosylation studies indicated that stanniocalcin from both sources contained N-linked oligosaccharides but no O-linked sugars. In an in vivo bioassay based on the inhibition of gill calcium transport in fishes, the baculovirus and CHO-expressed protein showed biological activity which is dose dependent. The inhibitory effects of hSTC produced from both systems were essentially equipotent in fishes, despite the differences in glycosylation. Consequently, the precise role of the carbohydrate moiety in recombinant hSTC remains to be determined.

Neuroserpin, a brain-associated inhibitor of tissue plasminogen activator is localized primarily in neurons. Implications for the regulation of motor learning and neuronal survival

A cDNA clone for the serine proteinase inhibitor (serpin), neuroserpin, was isolated from a human whole brain cDNA library, and recombinant protein was expressed in insect cells. The purified protein is an efficient inhibitor of tissue type plasminogen activator (tPA), having an apparent second-order rate constant of 6. 2 x 10(5) M-1 s-1 for the two-chain form. However, unlike other known plasminogen activator inhibitors, neuroserpin is a more effective inactivator of tPA than of urokinase-type plasminogen activator. Neuroserpin also effectively inhibited trypsin and nerve growth factor-gamma but reacted only slowly with plasmin and thrombin. Northern blot analysis showed a 1.8 kilobase messenger RNA expressed predominantly in adult human brain and spinal cord, and immunohistochemical studies of normal mouse tissue detected strong staining primarily in neuronal cells with occasionally positive microglial cells. Staining was most prominent in the ependymal cells of the choroid plexus, Purkinje cells of the cerebellum, select neurons of the hypothalamus and hippocampus, and in the myelinated axons of the commissura. Expression of tPA within these regions is reported to be high and has previously been correlated with both motor learning and neuronal survival. Taken together, these data suggest that neuroserpin is likely to be a critical regulator of tPA activity in the central nervous system, and as such may play an important role in neuronal plasticity and/or maintenance.