Use of a Photoactivatable Taxol Analogue to Identify Unique Cellular Targets in Murine Macrophages: Identification of Murine CD18 as a Major Taxol-Binding Protein and a Role for Mac-1 in Taxol-Induced Gene Expression

• Published in: The Journal of immunology (1950) 1999-06, Vol.162 (12), p.7335-7342
• Main Authors: Bhat, Nayantara, Perera, Pin-Yu, Carboni, Joan M, Blanco, Jorge, Golenbock, Douglas T, Mayadas, Tanya N, Vogel, Stefanie N
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Carrier Proteins - isolation & purification; Carrier Proteins - metabolism; CD18 Antigens - isolation & purification; CD18 Antigens - metabolism; Cell Line; Cell Membrane - metabolism; CHO Cells; Cricetinae; Gene Expression Regulation - immunology; Humans; Immune Sera - pharmacology; Interleukin-12 - antagonists & inhibitors; Interleukin-12 - biosynthesis; Interleukin-12 - genetics; Interleukin-12 - secretion; Lipopolysaccharides - pharmacology; Macrophage-1 Antigen - genetics; Macrophage-1 Antigen - immunology; Macrophage-1 Antigen - physiology; Macrophages, Peritoneal - drug effects; Macrophages, Peritoneal - immunology; Macrophages, Peritoneal - metabolism; Mice; Mice, Inbred C3H; Mice, Inbred C57BL; Mice, Knockout; Molecular Sequence Data; Paclitaxel - analogs & derivatives; Paclitaxel - metabolism; Paclitaxel - pharmacology; Photoaffinity Labels - metabolism; RNA, Messenger - biosynthesis
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.162.12.7335

Taxol, a potent antitumor agent that binds beta-tubulin and promotes microtubule assembly, results in mitotic arrest at the G2/M phase of the cell cycle. More recently, Taxol was shown to be a potent LPS mimetic in murine, but not in human macrophages, stimulating signaling pathways and gene expression indistinguishably from LPS. Although structurally unrelated to LPS, Taxol's LPS-mimetic activities are blocked by inactive structural analogues of LPS, indicating that despite the species-restricted effects of Taxol, LPS and Taxol share a common receptor/signaling complex that might be important in LPS-induced human diseases. To identify components of the putatively shared Taxol/LPS receptor, a novel, photoactivatable Taxol analogue was employed to identify unique Taxol-binding proteins in murine macrophage membranes. Seven major Taxol-binding proteins, ranging from approximately 50 to 200 kDa, were detected. Although photoactivatable Taxol analogue failed to bind to CD14, the prominent Taxol-binding protein was identified as CD18, the approximately 96-kDa common component of the beta2 integrin family. This finding was supported by the concomitant failure of macrophage membranes from Mac-1 knockout mice to express immunoreactive CD18 and the major Taxol-binding protein. In addition, Taxol-induced IL-12 p40 mRNA was markedly reduced in Mac-1 knockout macrophages and anti-Mac-1 Ab blocked secretion of IL-12 p70 in Taxol- and LPS-stimulated macrophages. Since CD18 has been described as a participant in LPS-induced binding and signal transduction, these data support the hypothesis that the interaction of murine CD18 with Taxol is involved in its proinflammatory activity.