NCBI Summary:
Albumin is a soluble, monomeric protein which comprises about one-half of the blood serum protein. Albumin functions primarily as a carrier protein for steroids, fatty acids, and thyroid hormones and plays a role in stabilizing extracellular fluid volume. Mutations in this gene on chromosome 4 result in various anomalous proteins. Albumin is a globular unglycosylated serum protein of molecular weight 65,000. The human albumin gene is 16,961 nucleotides long from the putative 'cap' site to the first poly(A) addition site. It is split into 15 exons which are symmetrically placed within the 3 domains that are thought to have arisen by triplication of a single primordial domain. Albumin is synthesized in the liver as preproalbumin which has an N-terminal peptide that is removed before the nascent protein is released from the rough endoplasmic reticulum. The product, proalbumin, is in turn cleaved in the Golgi vesicles to produce the secreted albumin.
General function
Extracellular binding protein
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Cellular localization
Secreted
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Ovarian function
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Expression regulated by
FSH
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FSH modulatory effect on human granulosa cells: a gene-protein candidate for gonadotrophin surge-attenuating factor. Karligiotou E et al. Previous evidence indicates a homology of gonadotrophin surge-attenuating factor (GnSAF) to the carboxyl terminal of human serum albumin (HSA) and the ability of human granulosa cells to produce mRNA transcripts corresponding to this fragment, but the underlying mechanism is still unknown. This study investigated the role of FSH in vitro in the expression of the carboxyl terminal of HSA by human luteinized granulosa cells. Cells were cultured on poly-l-lysine-coated microscope slides in the absence or presence of 10ng/ml FSH, followed by in-situ hybridization and immunocytochemistry. In the presence of FSH, mRNA transcripts corresponding to the carboxyl terminal of the HSA gene and corresponding protein could be detected in comparable intensity to that seen by hepatic HepG2 cells (positive control). Significantly lower expression was detected in granulosa cells cultured without FSH addition (P<0.01), but no expression was detected in HeLa cells. These results demonstrate for the first time that FSH stimulates the expression of the carboxyl terminal fragment of the HSA gene and corresponding protein in human luteinized granulosa cells. Therefore, the carboxyl terminal of HSA has a functional role in the ovary and this further supports the notion that this HSA fragment is a GnSAF-bioactive entity. Gonadotrophin surge-attenuating factor (GnSAF) is a nonsteroidal ovarian substance which attenuates the endogenous LH surge in superovulated women. In-vivo and in-vitro evidence has shown that GnSAF is produced under the stimulation of FSH and may play a physiological role during the normal menstrual cycle. We have previously demonstrated that GnSAF has identity to the carboxyl terminal fragment of human serum albumin (HSA). In this study, we investigated the role of FSH on the expression of the carboxyl terminal fragment of HSA by human luteinizing granulosa cells in vitro. It is demonstrated for the first time that FSH stimulates the expression of this fragment of HSA gene and the corresponding protein in human luteinizing granulosa cells. This finding supports further the notion that this fragment of HSA is the GnSAF bioactive entity.
Ovarian localization
Granulosa
Comment
Expression of human serum albumin (HSA) mRNA in human granulosa cells: potential correlation of the 95 amino acid long carboxyl terminal of HSA to gonadotrophin surge-attenuating factor Karligiotou E, et al .
INTRODUCTION: According to previous studies, gonadotrophin surge-attenuating factor (GnSAF), which is assumed to be produced in human granulosa cells, has a homology with the carboxyl terminal of the human serum albumin (HSA) protein. In an attempt to validate these findings, whole or partial expression of the HSA gene was studied by RT-PCR analysis in human granulosa cells from women undergoing IVF treatment. METHODS: RT-PCR analysis of HSA RNA transcripts in luteinized granulosa cells was done in order to investigate the possible expression of the HSA gene. To ensure the specificity of PCR products, restriction enzyme and sequence analysis were performed. Western blot analysis was carried out to detect the possible expression of the albumin gene in granulosa cells. RESULTS: RT-PCR analysis and sequencing analysis of cDNA from granulosa cells revealed bands identical with those from the positive control for the amino as well as the carboxyl terminal corresponding to HSA gene at the cytoplasmic level. CONCLUSION: We have demonstrated that human granulosa cells express the carboxyl and amino terminal part of the HSA gene in levels comparable to those found in human hepatocytes. It is suggested that the coding gene for GnSAF may be a result of an alternative expression of HSA gene.