Purification of a candidate gonadotrophin surge‐inhibiting/attenuating factor (GnSIF/AF) showing MAPK as a possible target

Abstract

Gonadotrophin surge-inhibiting/attenuating factor (GnSIF/AF) has been known for over two decades, but its molecular structure has not been completely characterized yet. In the last 20 years, five different putative GnSIF/AF sequences have been published. In this article, we describe a procedure to isolate and characterize GnSIF/AF from bovine follicular fluid, a GnSIF/AF-derived synthetic peptide (SP-GnSIF/AF) was produced, and the intracellular bioactivity of GnSIF/AF was tested for intracellular action with a MAPK-assay. Two different bioactive molecular weight forms of GnSIF/AF were isolated, a 160 kDa heteromeric and a monomeric 40 kDa protein. The 40 kDa form appeared to be a subunit of the 160 kDa protein. The synthetic peptide mimicked the actions of GnSIF/AF, such as inhibition of GnRH-induced LH secretion and attenuation of the MAPK phosphorylation. The two GnSIF/AF candidates do not show similarities with previously published GnSIF/AF sequences. These are the first data showing the influence of GnSIF/AF on intracellular processes involved in GnRH self-priming and that the biological action of GnSIF/AF was preserved in the produced synthetic peptide. The results provide strong evidence that the identified candidate proteins are the true GnSIF/AF.

Ghrelin Is a Novel Regulator of GLP-1 Secretion

“…Our findings therefore indicate that ghrelin alone does not lead to increases in GLP-1 but, rather, induces "priming" of the L-cell in preparation for subsequent oral glucose-stimulated GLP-1 secretion. Interestingly, the concept of priming has been established for other endocrine cells, including the effects of acetylcholine, g-aminobutyric acid, and fatty acids on subsequent insulin release by the b-cell (27)(28)(29), as well as of a novel modulatory factor that modulates gonadotrope secretion of luteinizing hormone (30).…”

DING Proteins from Phylogenetically Different Species Share High Degrees of Sequence and Structure Homology and Block Transcription of HIV-1 LTR Promoter

“…The DING proteins form an intriguing family of biologically active factors contributing to protective [7], [15], [16], [27], [42], [43] or possibly adverse [1], [6] cellular functions. In this work we selected four distinct members of the DING family to ascertain their structural and functional properties with specific interest in their anti-HIV-1 activity.…”

“…The biology of eukaryotic DING proteins as a group remains to be defined, but most DING proteins isolated from eukaryotes were related to a broad range of disorders and biological processes [1], [2], [6], [7], [15], [16], [17]. For example, the synovial stimulatory protein (SSP) has the capacity to induce proliferation of the peripheral blood T cells in patients with rheumatoid arthritis [6].…”

“…Another DING protein, the steroidogenesis-Inducing protein (SIP) has mitogenic activity toward the ovarian epithelium and might be involved in the etiology of ovarian cancer [18]. In contrast, a recent report by Hendriks et al indicated that dysfunction of the newly-characterized bovine DING homologue, the gonadotropin surge-Inhibiting/attenuating factor (GnSIF/AF) could lead to polycystic ovarian syndrome [15]. The crystal adhesion inhibitor (CAI), found in monkey and in human renal epithelial cells, has been shown to inhibit the growth of kidney stones [16].…”

Influence of ovarian manipulation on reproductive endocrinology in polycystic ovarian syndrome and regularly cycling women

“…GnSIF/AFs cannot be measured directly, because its molecular structure has not been fully identified yet. GnSIF/AF normally influences LH through inhibition of the GnRH-induced LH secretion and antagonizing the self-priming effect of GnRH (35,36,37). All measurable ovarian hormones in this study did not change, thus it is not likely that GnSIF/AF would be the only ovarian hormone that would change after the manipulation.…”