Novel Androgen-Dependent Promoters Direct Expression of the C4b-Binding Protein α-Chain Gene in Epididymis

Abstract

C4b-binding protein (C4BP) is a large plasma protein composed of seven α-chains and one β-chain and is involved in the fluid phase regulation of the classical pathway of the complement system. Complement inhibitory activity is located in the α-chain, and its mRNA has been detected only in liver to date. Here, we have isolated cDNA clones encoding the α-chain of guinea pig C4BP (C4BPα) and have demonstrated significant C4BPα mRNA expression in epididymis as well as liver. The level of C4BPα transcripts increased in the epididymis after birth, while it remained constant in the liver. C4BPα mRNA was also detected in the normal murine epididymis at a significant level, but it decreased drastically after castration, suggesting that epididymal expression of the C4BPα gene is regulated by androgen. Gene analysis of guinea pig C4BPα indicated that liver and epididymis C4BPα mRNA share the coding region and 3′-untranslated region, but are transcribed from independent promoters on a single-copy gene. Two novel epididymis-specific promoters were identified in the region corresponding to the first intron of liver transcripts. The binding motif for hepatocyte NF-1 occurs in the promoter used for transcription of liver C4BPα, whereas androgen-responsive elements occur in both promoters used in the epididymis. These findings present a novel link between complement regulators and reproduction. Furthermore, variation in the 5′-untranslated regions, arising from alternative splicing of the newly identified exons, is demonstrable in the guinea pig C4BPα transcripts.

Disruption of Mouse CD46 Causes an Accelerated Spontaneous Acrosome Reaction in Sperm

“…Interestingly, in the rodent animals studied, the expression of CD46 was limited only in testis, indicating that the major function of CD46 among different species lies in fertilization. Moreover, in rodent animals, distribution of complement regulators such as transmembrane type CD55 (decay accelerating factor [DAF]), CD59b, and C4b-binding protein were preferentially expressed in reproductive organs (4,25,30,37,42). In humans, CD46 is expressed on the membrane of all kinds of nucleated cells.…”

Complement C4b-Binding Protein as a Novel Murine Epididymal Secretory Protein

“…In the previous report [16], we also demonstrated that murine epididymis express, in an androgen-dependent manner, the transcripts that hybridize with C4BP␣ cDNA. In the present report, we confirmed that these species are transcribed from the C4bpa gene and detected the protein in the epididymis by Western blot analysis and immunohistochemistry.…”

“…However, this site was not detected in our experiments. Although further analyses are necessary, Lt is more likely to be a transcription start site, because Lt is located downstream of a hepatocyte nuclear factor-1 (HNF-1) response element and is in a comparable position with the major transcription start site of the human (position ϩ11) [39], guinea pig (position ϩ2) [16], and rat (position Ϫ9) [40] C4BP␣ genes.…”

“…They are located within the acrosomal region and are thought to interact with oocytes after the acrosome reaction occurs. Furthermore, we demonstrated recently that C4BP␣ mRNA is expressed in guinea pig epididymis in an androgen-dependent manner [16].…”

“…The C4BP is a large, heterogeneous plasma protein (M r 540 000-590 000) and has been isolated and/or cloned from several animals [16][17][18][19][20][21][22][23][24]. The major isoform of human C4BP is composed of seven ␣ chains of M r 70 000 and one ␤ chain of M r 30 000, which bind covalently to each other via the C-terminal regions.…”