It is well established that celecoxib, a selective inhibitor of cyclooxygenase-2 (COX-2) and a tested chemopreventive agent, has several COX-2-independent activities. In an attempt to better understand COX-2-independent molecular mechanisms underlying the chemopreventive activity of celecoxib, we did global transcription profiling of celecoxib-treated COX-2-positive and COX-2-deficient colorectal cancer cell lines. Celecoxib treatment resulted in significantly altered expression levels of over 1,000 to 3,000 transcripts in these cell lines, respectively. A pathway/functional analysis of celecoxib-affected transcripts, using Gene Ontology and Biocarta Pathways and exploring biological association networks, revealed that celecoxib modulates expression of numerous genes involved in a variety of cellular processes, including metabolism, cell proliferation, apoptotic signaling, cell cycle check points, lymphocyte activation, and signaling pathways. Among these processes, cell proliferation and apoptotic signaling consistently ranked as the highest-scoring Gene Ontology terms and Biocarta Pathways in both COX-2 expresser and nonexpresser cell lines. Altered expression of many of the genes by celecoxib was confirmed by quantitative PCR and at the protein level by Western blotting. Many novel genes emerged from our analysis of global transcription patterns that were not previously reported to be affected by celecoxib. In the future, in-depth work on selected genes will determine if these genes may serve as potential molecular targets for more effective chemopreventive strategies.

The high-affinity NGF receptor is thought to be a complex of two receptors , gp75 and the tyrosine kinase TrkA, but direct biochemical evidence for such an association had been lacking. In this report, we demonstrate the existence of such a gp75-TrkA complex by a copatching technique. Gp75 on the surface of intact cells is patched with an anti-gp75 antibody and fluorescent secondary antibody, the cells are then fixed to prevent further antibody-induced redistributions, and the distribution of TrkA is probed with and anti-TrkA antibody and fluorescent secondary antibody. We utilize a baculovirus-insect cell expression of wild-type and mutated NGF receptors. TrkA and gp75 copatch in both the absence and presence of NGF. The association is specific, since gp75 does not copatch with other tyrosine kinase receptors, including TrkB, platelet-derived growth factor receptor-beta, and Torso (Tor). To determine which domains of TrkA are required for copatching, we used a series of TrkA-Tor chimeric receptors and show that the extracellular domain of TrkA is sufficient for copatching with gp75. A chimeric receptor with TrkA transmembrane and intracellular domains show partial copatching with gp75. Deletion of the intracellular domain of gp75 decreases but does not eliminate copatching. A point mutation which inactivates the TrkA kinase has no effect on copatching, indicating that this enzymatic activity is not required for association with gp75. Hence, although interactions between the gp75 and TrkA extracellular domains are sufficient for complex formation, interactions involving other receptor domains also play a role.