PubMed Health⌕ Search

Biomedical subjects

N S Longo

Publications and source records attributed to N S Longo.

5 recordsLinked to original sources
PubMed2000

Lck domains differentially contribute to pre-T cell receptor (TCR)- and TCR-alpha/beta-regulated developmental transitions.

Maturational changes at the CD4(-)CD8(-) double negative (DN) to CD4(+)CD8(+) double positive (DP) transition are dependent on signals generated via the pre-T cell receptor (TCR) and the nonreceptor protein tyrosine kinase p56(lck) (Lck). How Lck activities are stimulated or relayed after pre-TCR formation remains obscure. Our structure-function mapping of Lck thymopoietic properties reveals that the noncatalytic domains of Lck are specialized to signal efficient cellular expansion at DN to DP transition. Moreover, although substitution of the Lck catalytic domain with FynT sequences minimally impacts DP development, single positive thymocytes are most efficiently produced in the presence of kinases containing both the NH(2)-terminal and catalytic regions of Lck. These findings demonstrate that the Lck structure is uniquely adapted to mediate signals at both major transitions in thymopoiesis.

Animals↗
PubMed1980

The pulmonary clara cell as a target for toxic chemicals requiring metabolic activation; studies with carbon tetrachloride.

Oral administration of carbon tetrachloride to rats or mice caused striking decreases in rat lung microsomal cytochrome P-450 and benzphetamine demethylase activity and in the enzyme-mediated covalent binding of 4-ipomeanol in preparations of rat and mouse lung microsomes, mouse lung slices and isolated whole-mouse lungs. Although it is not yet known whether cytochrome P-450 and benzphetamine demethylase activities are present in substantial amounts in more than one lung cell type in mice or rats, previous studies have indicated that cytochrome P-450 enzymes located in pulmonary bronchiolar Clara cells of these mediate the covalent binding of 4-ipomeanol to lung macromolecules. Histologic examinations of lungs of animals given doses of CCl4, orally or by inhalation, revealed striking morphologic changes in Clara cells, including severe dilation of endoplasmic reticulum and occasional cellular necrosis. Because of cytochrome P-450 enzymes are capable of mediating the formation of highly reactive and potentially toxic-free radicals from CCl4, the present results support the view that pulmonary Clara cells are susceptible to CCl4-induced injury due to their capacity to metabolically activate the chemical.

Animals↗
PubMedDate not supplied

Regulation of Src-family protein tyrosine kinase transcription during lymphocyte ontogeny.

The distribution and quantity of cellular signaling elements influence response patterns to a variety of stimuli. As protein tyrosine phosphorylation is a requisite event induced by a majority of surface receptors, and protein tyrosine kinases of the src-family (src-PTKs) act as proximal transducers for many hematopoietic receptors, we have designed a quantitative RT-PCR assay to measure src-family PTK expression during critical stages of lymphocyte ontogeny. With this assay we demonstrate that the distal promoter element regulating expression of lck, a src-PTK essential for T-cell development and activation, is similarly regulated during ontogeny of T and B cells. However, lck transcript abundance is drastically reduced in B lineage cells, suggesting that transcriptional elements influencing lck promoter activity are modulated in these cells. Moreover, although transcripts encoding the src-PTK fyn accumulate at 0.1% of lck mRNA levels in thymocytes, diminished activity of the lck distal promoter in the B-cell background brings lck and fyn transcript levels to near equivalence in this population. Importantly, transcripts arising from the lck distal promoter element and the fyn locus are similarly upregulated during developmental transitions associated with antigen-receptor expression in both B and T cells. These findings suggest that although the magnitude of lck and fyn expression is differentially regulated in B and T cells, expression at these loci is similarly developmentally programmed during ontogeny of both lymphocyte lineages.

Animals↗