title: Cysteine proteases and cell differentiation: excystment of the ciliated protist Sterkiella histriomuscorum.
abstract: The process of excystment of Sterkiella histriomuscorum (Ciliophora, Oxytrichidae) leads in a few hours, through a massive influx of water and the resorption of the cyst wall, from an undifferentiated resting cyst to a highly differentiated and dividing vegetative cell. While studying the nature of the genes involved in this process, we isolated three different cysteine proteases genes, namely, a cathepsin B gene, a cathepsin L-like gene, and a calpain-like gene. Excystation was selectively inhibited at a precise differentiating stage by cysteine proteases inhibitors, suggesting that these proteins are specifically required during the excystment process. Reverse transcription-PCR experiments showed that both genes display differential expression between the cyst and the vegetative cells. A phylogenetic analysis showed for the first time that the cathepsin B tree is paraphyletic and that the diverging S. histriomuscorum cathepsin B is closely related to its Giardia homologues, which take part in the cyst wall breakdown process. The deduced cathepsin L-like protein sequence displays the structural signatures and phylogenetic relationships of cathepsin H, a protein that is known only in plants and animals and that is involved in the degradation of extracellular matrix components in cancer diseases. The deduced calpain-like protein sequence does not display the calcium-binding domain of conventional calpains; it belongs to a diverging phylogenetic cluster that includes Aspergillus palB, a protein which is involved in a signal transduction pathway that is sensitive to ambient pH.
authors.affiliation: Laboratoire de Biologie Cellulaire 4, Université de Paris-Sud, Orsay, France.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Villalobo
authors.forename: Clara
authors.initials: C
authors.lastname: Moch
authors.forename: Ghislaine
authors.initials: G
authors.lastname: Fryd-Versavel
authors.forename: Anne
authors.initials: A
authors.lastname: Fleury-Aubusson
authors.forename: Loïc
authors.initials: L
authors.lastname: Morin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D002473:Cell Wall / Q000187:drug effects; D016798:Ciliophora / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D017124:Conserved Sequence; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D017125:Genes, Protozoan; D007976:Leupeptins / Q000494:pharmacology; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
chemical_list: C400541:CA 074 methyl ester; D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D007976:Leupeptins; D015800:Protozoan Proteins; C068250:N-(3-propylcarbamoyloxirane-2-carbonyl)-isoleucyl-proline; D003546:Cysteine Endopeptidases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde