Promoter analysis of the TCA3 chemokine gene identified minimal promoter sequences contained within the 0.082 kb upstream region of the TCA3 gene with a putative enhancer NF-kB element between -0.324 kb and -0.136 kb and a putative inhibitory element between -1.324 kb and -2.0 kb upstream from the transcription start site. Functional assessment of the region between -1.324kb and -2kb demonstrated that there are at least two negative regulatory elements (NREs) that control the transcription of the TCA 3 gene in activated mast cells. Both NREs inhibited the activity of a CD20-CAT construct in mast cells, independent of cell activation. One NRE was similar to a putative silencer motif in the alpha2b integrin gene. The second NRE was novel and was characterized by a CT-rich sequence. Mast cells transfected with a TCA3-CAT construct and co- cultured with activated lymphocytes, exhibited an increase in CAT expression. Supernatants from activated lymphocytes had no effect. This data demonstrates that activated lymphocytes have the ability to induce the promoter of the TCA3 gene in mast cells through cell-to-cell contact. The trkA tyrosine kinase receptor functions as a signal transducing receptor for nerve growth factor (NGF). By Northern blot analysis we have found that HMC-1 cells, (a human mast cell line) express mRNA for trkA, but not for other high affinity neurotrophin receptors, nor the low affinity neurotrophin receptor p75. Expression of trkA protein was demonstrated by Western blot and immunohistochemistry. The trkA receptors expressed on HMC-1 are functional in that NGF significantly increased the mRNA levels for the early response gene c-fos.
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