Identification of tgh-2, a filarial nematode homolog of Caenorhabditis elegans daf-7 and human transforming growth factor beta, expressed in microfilarial and adult stages of Brugia malayi

A novel member of the transforming growth factor beta (TGF-beta) family has been identified in the filarial nematode parasite Brugia malayi by searchi ng the recently developed Expressed Sequence Tag (EST) database produced by the Filarial Genome Project. Designated tgh-2, this new gene shows most si milarity to a key product regulating dauer larva formation in Caenorhabditi s elegans (DAF-7) and to the human down-modulatory cytokine TGF-beta. Homol ogy to DAF-7 extends throughout the length of the 349-amino-acid (aa) prote in, which is divided into an N-terminal 237 aa, including a putative signal sequence, a 4-aa basic cleavage site, and a 108-aa C-terminal active domai n. Similarity to human TGF-beta is restricted to the C-terminal domain, ove r which there is a 32% identity between TGH-2 and TGF-beta1, including ever y cysteine residue. Expression of tgh-2 mRNA has been measured over the fil arial life cycle. It is maximal in the microfilarial stage, with lower leve ls of activity around the time of molting within the mammal, but continues to be expressed by mature adult male and female parasites. Expression in bo th the microfilaria, which is in a state of arrested development, and the a dult, which is terminally differentiated, indicates that tgh-2 may play a r ole other than purely developmental. This is consistent with our observatio n that TGH-2 is secreted by adult worms in vitro. Recombinant TGH-2 express ed in baculovirus shows a low level of binding to TGF-beta -receptor bearin g mink lung epithelial cells (MELCs), which is partially inhibited (16 to 3 9%) with human TGF-beta, and activates plasminogen activator inhibitor-1 tr anscription in MELCs, a marker for TGF-beta -mediated transduction. Further tests will be required to establish whether the major role of B. malayi TG H-2 (Bm-TGH-2) is to modulate the host immune response via the TGF-beta pat hway.