Mutations of the gene Lps selectively impede lipopolysaccharide (LPS) signal transduction in C3H/HeJ and C57BL/10ScCr mice, rendering them resistant to endotoxin yet highly susceptible to Gram-negative infection. The codominant Lpsd allele of C3H/HeJ mice was shown to correspond to a missense mutation in the third exon of the Toll-like receptor-4 gene (Tlr4), predicted to replace proline with histidine at position 712 of the polypeptide chain. C57BL/10ScCr mice are homozygous for a null mutation of Tlr4. Thus, the mammalian Tlr4 protein has been adapted primarily to subserve the recognition of LPS and presumably transduces the LPS signal across the plasma membrane. Destructive mutations of Tlr4 predispose to the development of Gram-negative sepsis, leaving most aspects of immune function intact.

http://science.sciencemag.org/content/sci/282/5396/2085.full.pdf

Defective LPS Signaling in C3H/HeJ and C57BL/10ScCr Mice: Mutations in Tlr4 Gene

Defective LPS signaling in C3 H/HeJ and C57 BL/10 ScCr mice: Mutations in Tlr4 Gene

Leukocytes respond to lipopolysaccharide (LPS) at nanogram per milliliter concentrations with secretion of cytokines such as tumor necrosis factor-alpha (TNF-alpha). Excess secretion of TNF-alpha causes endotoxic shock, an often fatal complication of infection. LPS in the bloodstream rapidly binds to the serum protein, lipopolysaccharide binding protein (LBP), and cellular responses to physiological levels of LPS are dependent on LBP. CD14, a differentiation antigen of monocytes, was found to bind complexes of LPS and LBP, and blockade of CD14 with monoclonal antibodies prevented synthesis of TNF-alpha by whole blood incubated with LPS. Thus, LPS may induce responses by interacting with a soluble binding protein in serum that then binds the cell surface protein CD14.

https://science.sciencemag.org/content/sci/249/4975/1431.full.pdf

CD14, a receptor for complexes of lipopolysaccharide (LPS) and LPS binding protein.

https://www.cell.com/cell/pdf/0092-8674(86)90341-7.pdf

A conserved AU sequence from the 3′ untranslated region of GM-CSF mRNA mediates selective mRNA degradation

The t(14; 18) chromosomal translocation of human follicular B-cell lymphoma juxtaposes the bcl-2 gene with the immunoglobulin heavy chain locus. The bcl-2 immunoglobulin fusion gene is markedly deregulated resulting in inappropriately elevated levels of bcl-2 RNA and protein. Transgenic mice bearing a bcl-2 immunoglobulin minigene demonstrate a polyclonal expansion of resting yet responsive IgM-IgD B cells which display prolonged cell survival but no increase in cell cycling. Moreover, deregulated bcl-2 extends the survival of certain haematopoietic cell lines following growth-factor deprivation. By using immunolocalization studies we now demonstrate that Bcl-2 is an integral inner mitochondrial membrane protein of relative molecular mass 25,000 (25k). Overexpression of Bcl-2 blocks the apoptotic death of a pro-B-lymphocyte cell line. Thus, Bcl-2 is unique among proto-oncogenes, being localized to mitochondria and interfering with programmed cell death independent of promoting cell division.

Bcl-2 is an inner mitochondrial membrane protein that blocks programmed cell death

The primary structure of lipopolysaccharide binding protein (LBP), a trace plasma protein that binds to the lipid A moiety of bacterial lipopolysaccharides (LPSs), was deduced by sequencing cloned complementary DNA. LBP shares sequence identity with another LPS binding protein found in granulocytes, bactericidal/permeability-increasing protein, and with cholesterol ester transport protein of the plasma. LBP may control the response to LPS under physiologic conditions by forming high-affinity complexes with LPS that bind to monocytes and macrophages, which then secrete tumor necrosis factor. The identification of this pathway for LPS-induced monocyte stimulation may aid in the development of treatments for diseases in which Gram-negative sepsis or endotoxemia are involved.

https://science.sciencemag.org/content/sci/249/4975/1429.full.pdf

Structure and function of lipopolysaccharide binding protein

A cDNA sequence coding for human immune interferon (IFN-γ) has been identified in a cDNA library prepared from gel-fractionated IFN-γ mRNA. The DNA sequence codes for a polypeptide of 166 amino acids, 20 of which could constitute a signal peptide. The polypeptide produced through expression of this DNA sequence in Escherichia coli or cultured monkey cells had properties characteristic of authentic human IFN-γ.

Expression of human immune interferon cDNA in E. coli and monkey cells

A chemically-synthesized gene and natural complementary DNA coding for human lymphotoxin were isolated and engineered for expression in Escherichia coli. Purified recombinant lymphotoxin shows cytotoxic activity on murine and human tumour cell lines in vitro and causes necrosis of certain murine sarcomas in vivo.

Cloning and expression of cDNA for human lymphotoxin, a lymphokine with tumour necrosis activity.

Human Tumor Necrosis Factor and Lymphotoxin are cytotoxic proteins which have similar biological activities and share 30 percent amino acid homology. The single copy genes which encode these proteins share several structural features: each gene is approximately three kilobase pairs in length and is interrupted by three introns. In addition, these genes are closely linked and have been mapped to human chromosome 6. However, only the last exons of both genes, which code for more than 80 percent of each secreted protein, are significantly homologous (56 percent).

Human Lymphotoxin and tumor necrosis factor genes: structure, homology and chromosomal localization

Eight classes of human leukocyte interferon (LeIFN) cDNA clones have been identified in a cDNA library prepared from a myeloblastoid cell line. The nucleotide sequences demonstrate that the multiple human LeIFN genes code for a family of homologous, yet distinct proteins. One of the cDNA clones may have been derived from the transcription of a LeIFN pseudogene.

Patrick W. Gray

Papers

Structure and function of lipopolysaccharide binding protein

Expression of human immune interferon cDNA in E. coli and monkey cells

Cloning and expression of cDNA for human lymphotoxin, a lymphokine with tumour necrosis activity.

Human Lymphotoxin and tumor necrosis factor genes: structure, homology and chromosomal localization

The structure of eight distinct cloned human leukocyte interferon cDNAs.