Identification and characterization of Cystatin-related epididymal and spermatogenic (CRES) expression in anterior pituitary gonadotropes

Date

2001-08

Journal Title

Journal ISSN

Volume Title

Publisher

Texas Tech University

Abstract

Male factor infertility contributes to half of all infertility cases, yet current knowledge remains unable to diagnose all but gross abnormalities in male reproductive physiology. In an effort to identify proteins involved in initiating epididymal sperm maturation, our lab identified the cystatin-related epididymal spermatogenic (CRES) gene based on its preferential expression in the initial epididymal segment. Cres represents a unique subgroup of the cystatin family of cysteine protease inhibitors in that its expression is restricted to reproductive tissues and its sequence predicts specificity distinct from classic cystatins. CRES protein is localized to the caput epididymal lumen and the sperm acrosome. Both compartments contain active proteases responsible for protein processing events that are required for sperm function; however, the regulatory mechanisms controlling these processing events are poorly understood. These observations led to the proposal that CRES protein regulates protein processing in these tissues.

We hypothesized that CRES might also regulate proteolysis in the pituitary gland for two reasons: (1) the pituitary gland expresses a number of proteases involved in preprotein processing; and (2) the pituitary gland is functionally connected with the gonad via the hypothalamic-pituitary-gonadal axis. Thus, the goal of these studies was to determine whether CRES is expressed in the pituitary gland and if so, to examine its regulation by hypothalamic and/or gonadal factors. These studies demonstrate that CRES is expressed in the anterior pituitary gland and is co-localized intracellularly with leutinizing hormone (LH) in gonadotrope secretory granules. To examine the regulation of Cres mRNA, we developed a semi-quantitative RT-PCR assay and showed that, unlike steroid hormones, GnRH is the primary physiologic regulator of Cres gene expression. Specifically, GnRH administration causes a rapid decrease in Cres mRNA levels, an effect opposite from its potent stimulation of LHp mRNA expression. In contrast, intracellular CRES and LHP protein levels were regulated similarly by steroid hormones, consistent with their being packaged within the same subset of secretory granules. Taken together, these studies indicate that CRES function is influenced by subtle alterations in the hypothalamic-pituitary-gonadal axis, suggesting it may regulate processing events important at specific times for gonadotrope secretory functions.

Description

Keywords

Epididymis -- Physiology, Spermatogenesis, Gonadotropin -- Physiology, LH -- Analysis, Gene expression regulation, Cystatins -- Analysis, Gene expression, Anterior -- Chemistry, Pituitary gland, Cysteine proteinases, Cystatins -- Genetics, Hypothalamic-pituitary-adrenal axis -- Physiology, Luteinizing hormone releasing hormone, Epididymis

Citation