RESUMO
A novel heterodimeric glycoprotein hormone (GpH) comprised of alpha (GpA2) and beta (GpB5) subunits was discovered in 2002 and called thyrostimulin for its ability to activate the TSH receptor in mammals, but its central function in vertebrates has not been firmly established. We report here the cloning and expression of lamprey (l)GpB5, and its ability to heterodimerize with lGpA2 to form a functional l-thyrostimulin. The full-length cDNA of lGpB5 encodes 174 amino acids with ten conserved cysteine residues and one glycosylation site that is conserved with other vertebrate GpB5 sequences. Phylogenetic and synteny analyses support that lGpB5 belongs to the vertebrate GpB5 clade. Heterodimerization of lGpB5 and lGpA2 was shown by nickel pull-down of histidine-tagged recombinant subunits. RNA transcripts of lGpB5 were detected in the pituitary of lampreys during both parasitic and adult life stages. Intraperitoneal injection with lGnRH-III (100⯵g/kg) increased pituitary lGpA2, lGpB5, and lGpHß mRNA expression in sexually mature, adult female lampreys. A recombinant l-thyrostimulin produced by expression of a fusion gene in Pichia pastoris activated lamprey GpH receptors I and II as measured by cAMP enzymeimmunoassay. In contrast to jawed vertebrates that have pituitary LH, FSH, and TSH, our data support that lampreys only have two functional pituitary GpHs, lGpH and l-thyrostimulin, which consist of lGpA2 and unique beta subunits. It is hypothesized that lGpH and l-thyrostimulin differentially regulate reproductive and thyroid activities in some unknown way(s) in lampreys.
Assuntos
Subunidade alfa de Hormônios Glicoproteicos/genética , Glicoproteínas/genética , Lampreias/metabolismo , Sequência de Aminoácidos , Animais , Sequência de Bases , Clonagem Molecular , Feminino , Perfilação da Expressão Gênica , Subunidade alfa de Hormônios Glicoproteicos/química , Subunidade alfa de Hormônios Glicoproteicos/metabolismo , Hormônio Liberador de Gonadotropina/metabolismo , Lampreias/crescimento & desenvolvimento , Estágios do Ciclo de Vida , Filogenia , Multimerização Proteica , Proteínas Recombinantes/metabolismo , Sintenia/genética , Distribuição TecidualRESUMO
The gnathostome (jawed vertebrates) classical pituitary glycoprotein hormones, FSH, LH, and TSH, consist of a common α-subunit (GpA1) and unique ß-subunits (Gpß1, -2, and -3), whereas a recently identified pituitary glycoprotein hormone, thyrostimulin, consists of GpA2 and GpB5. This paper reports the identification, expression, and function of an ancestral, nonclassical, pituitary heterodimeric glycoprotein hormone (GpH) consisting of the thyrostimulin A2 subunit with the classical ß-subunit in the sea lamprey, Petromyzon marinus, a jawless basal vertebrate. Lamprey (l) GpA2, and lGpHß were shown to form a heterodimer by coimmunoprecipitation of lGpA2 with FLAG-tagged lGpHß after the overexpression in transiently transfected COS7 cells using a bipromoter vector. Dual-label fluorescent in situ hybridization and immunohistochemistry showed the coexpression of individual subunits in the proximal pars distalis of the pituitary. GnRH-III (1µΜ) significantly increased the expression of lGpHß and lGpA2 in in vitro pituitary culture. Recombinant lamprey GpH was constructed by tethering the N terminal of lGpA2 to the C terminal of lGpHß with a linker region composed of six histidine residues followed by three glycine-serine repeats. This recombinant lamprey GpH activated the lamprey glycoprotein hormone receptor I as measured by increased cAMP/luciferase activity. These data are the first to demonstrate a functional, unique glycoprotein heterodimer that is not found in any other vertebrate. These data suggest an intermediate stage of the structure-function of the gonadotropin/thyroid-stimulating hormone in a basal vertebrate, leading to the emergence of the highly specialized gonadotropin hormones and thyroid stimulating hormones in gnathostomes.
