Pathogenic Neisseria species, the causative agents of gonorrhoea and bacterial meningitis, encode a family of polymorphic exo-proteins which are autoproteolytically processed into several distinct extracellular components, including an IgA1 protease and an alpha-protein. IgA1 protease, a putative virulence determinant, is a sequence-specific endopeptidase known to cleave human IgA1, but additional target proteins have been postulated. The physical linkage of IgA1 protease and alpha-protein suggests a functional relationship of both precursor components. Previous work has shown that alpha-protein is essential neither for extracellular transport nor for the proteolytic activity of IgA1 protease. Intriguingly, alpha-proteins carry amino acid sequences reminiscent of nuclear location signals of viral and eukaryotic proteins. Here we demonstrate the functionality of these nuclear location signal sequences in transfected eukaryotic cells. Chimeric alpha-proteins show nuclear transport and selectively associate with nucleolar structures. More importantly, native purified alpha-proteins are capable of entering certain human primary cells from the exterior via an endocytotic route and accumulate in the nuclei. The neisserial alpha-proteins share several features with eukaryotic transcription factors, such as the formation of dimers via a heptad repeat sequence. We propose a role for alpha-proteins in the regulation of host-cell functions. As the alpha-proteins are covalently connected with IgA1 protease they may also serve as carries for the IgA1 protease into human cells where additional proteolytic targets may exist. Neisseria meningitidis, which locally colonizes the nasopharyngeal mucosa of many human individuals without apparently causing symptoms, secretes this nucleus-targeted factor in large quantities.
Mycoplasmal infections still cause severe problems in cell cultures, particularly permanent lines, and although rapid detection is possible the only methods proposed for the elimination of the mycoplasma are either laborious or unsatisfactory. Treatment with antibiotics often leads to the development of resistance and we have found it more successful to passage contaminated cells in nude (thymusless) mice although the cells cannot always be recovered. But when the resulting subcutanous tumours can be collected, the cells are both free of mycoplasma and accompanied by a large number of macrophages. Because nude mice have no T cell-dependent immune response, it seemed possible that the macrophages could be responsible for the elimination of the mycoplasma. The experiments reported here support this hypothesis, and have led to a rapid and reproducible technique for eliminating mycoplasma in vitro by a brief co-cultivation of contaminated cells with mouse macrophages, in the presence of antibiotics.
Cleaning of human tumor cell lines from arginine-dependent nonfermentative Mycoplasma orale 1 (MO1) by a recently developed technique profoundly altered several in vitro properties of the cell lines. Four melanoma lines (Mel I, Mel St, Mel K, IGR3) and 1 ovarian carcinoma line (Ro) induced human leukocyte interferon (IFN-alpha) only in the mycoplasma-infected state and not in the mycoplasma-free state. MO1-infected tumor lines were generally more susceptible to natural killer (NK) cell-mediated lysis than their mycoplasma-free counterparts. Reinfection of cleaned tumor lines with MO1 restored their interferonogenicity and the increased susceptibility to NK lysis. Thus, the amplifying role of MO1 infection on NK target lysis occurred in connection with an increased production IFN-alpha during the assay period. The human erythroleukemia cell line K562 was exceptional in that it also induced high levels of IFN in an apparently mycoplasma-free state and was unaffected in its susceptibility ot NK lysis by infection with MO1. Possible implications of these findings for the biologic significance of the NK reaction are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.