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General Comment |
Proprotein convertases are calcium-dependent serine proteases related to bacterial subtilisins and to yeast kexin. These
enzymes process precursor proteins to their active forms by selective cleavage of the polypeptide at sites following
paired basic amino acids.
Proprotein convertase subtilisin/kexin type 4 in mammalian fertility: a review. Gyamera-Acheampong C et al. BACKGROUND Proprotein convertase subtilisin/kexin type 4 (PCSK4), also known as proprotein convertase 4, belongs to a family of endoproteinases involved in the proteolytic conversion of secretory precursor proteins to their active forms. Its amino acid sequence is highly conserved in mammals, an indication of its biological importance. METHODS We have searched PubMed and molecular biology databases for information relating to the structure, expression and biological functions of PCSK4. RESULTS PCSK4 is predominantly expressed in male germ cells and located on the plasma membrane overlying the acrosome of sperm. It is also present in ovary and placenta. Inactivation of its gene in mouse does not alter spermatogenesis, but renders sperm incapable of fertilizing oocytes. This incapacity results in part from sperm susceptibility to a premature acrosome reaction and their reduced ability to bind to the zona pellucida. In female mice, a lack of PCSK4 causes subfertility associated with impaired folliculogenesis. In addition, this enzyme has been shown to stimulate the invasiveness of human placental trophoblasts in culture, suggesting that it may facilitate placentation in vivo. CONCLUSIONS PCSK4 appears to be a crucial enzyme for reproduction. Alterations of PCSK4 expression or activity could be the underlying cause of some unexplained cases of human infertility. Conversely, inactivation of this protease represents a potential strategy for non-hormonal contraception.
NCBI Summary:
This gene encodes a member of the subtilisin-like proprotein convertase family. These enzymes process latent precursor proteins into their biologically active products. The encoded protein plays a critical role in reproduction and processes multiple prohormones including pro-pituitary adenylate cyclase-activating protein (proPACAP) and pro-insulin-like growth factor II. [provided by RefSeq, Feb 2012]
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Comment |
Min Li, et al 2000 analyzed testicular and ovarian extracts from the PC4-null and wild-type mice for PACAP (PACAP38 and
PACAP27) and its messenger RNA using reverse phase HPLC combined with specific RIAs and ribonuclease protection
assay, respectively. For RIAs, three different polyclonal antisera with different recognition sites were used to identify
PACAP38, PACAP27, and its precursor. Neither the testis nor the ovary from the PC4-null mice expressed PACAP38 or
PACAP27, but the levels of PACAP transcripts in the testis and ovary of homozygous PC4-deficient mice were considerably
elevated compared with those of the wild-type and heterozygous animals. The findings indicate that PC4 is the sole
processing enzyme for the precursor of PACAP in the testis and ovary of mice.
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Comment |
Tadros H, et al 2001 reported that the testicular germ-cell protease PC4 is also expressed in
macrophage-like cells of the ovary.
PC4 is a serine protease primarily expressed in spermatids. The authors have produced PC4-deficient mice carrying an insertion of the bacterial gene for beta galactosidase under the PC4 gene promoter. Male mice lacking PC4 (- / -)
exhibit severely reduced fertility. Surprisingly, the fertility of female mice is also significantly diminished in these mutants. Using a histoenzymatic assay for beta -galactosidase, the authors how that the PC4 promoter can drive strong expression of this enzyme in the theca-interstitium and in degenerating corpora lutea of
+/- ovaries. PC4 transcripts can be detected by RT-PCR in the ovaries of +/- and +/+ mice, but not in those of -/- mice. The cells expressing PC4 were macrophage-like, since they expressed the macrophage markers CD11b and F4/80, as well as interleukin 1 beta and tumor necrosis
factor alpha (TNF alpha). Expression of PC4 was also detected in the mouse macrophage RAW264.7 cell line. Interestingly, TNF alpha transcripts were
3-fold more abundant in ovarian macrophagelike cells from -/- mice than in
those from +/+ mice, suggesting a constitutive state of activation of the
mutant cells.
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Mutations |
2 mutations
Species: mouse
Mutation name: None
type: null mutation
fertility: subfertile
Comment: Mbikay M, et al 1997
have disrupted the PC4 locus (Pcsk4) by homologous recombination in embryonic stem
cells and have produced mice carrying the mutation. In intercrosses of
heterozygous mutant mice, there was low transmission of the mutant Pcsk4 allele
to the progeny, resulting in lower than expected incidence of heterozygosity and
null homozygosity. The in vivo fertility of homozygous mutant males was severely
impaired in the absence of any evident spermatogenic abnormality. In vitro, the
fertilizing ability of Pcsk4 null spermatozoa was also found to be significantly
reduced. Moreover, eggs fertilized by these spermatozoa failed to grow to the
blastocyst stage. Surprisingly, the fertility of female mice is also significantly diminished in these mutants.
Min Li, Majambu Mbikay, Akira Arimura reported the absence of PACAP in the Gonads of PC4-Deficient Mice with Impaired Fertility.
Pituitary adenylate cyclase-activating polypeptide (PACAP) is
abundant not only in the brain, but also in the testis and ovary.
In vitro enzymatic assay for
recombinant PC4 confirmed that PC4 is the best candidate enzyme
for processing proPACAP to PACAP38. In the testis, PC4 mRNA
is expressed in pachytene spermatocytes and round spermatids of
both the rat and mouse, and its expression is developmentally
regulated. The expression of PC4 transcripts precedes or overlaps
with the expression of PACAP-li in the germ cells. The
PC4-knockout mice developed severely impaired fertility without
any apparent abnormality of spermatogenesis. Moreover, the
oocytes from the wild-type animal fertilized with the spermatozoa
from PC4-null mouse failed to grow to the blastocyst stage,
resulting in early embryonic death. PC4 is also synthesized in the
ovary of females, and the PC4-null female mice showed retarded
folliculogenesis.
Species: mouse
Mutation name: None
type: null mutation
fertility: subfertile
Comment: Pituitary adenylate cyclase-activating polypeptide precursor is processed solely by prohormone convertase 4 in the gonads. Li M et al. Pituitary adenylate cyclase-activating polypeptide (PACAP) is abundant not only in the brain, but also in the testis. Immunohistochemical studies have shown that PACAP-LI in rat testis is expressed stage specifically in spermatids. This suggests that testicular PACAP participates in the regulatory mechanism of spermatogenesis. Additionally, the ovary contains a relatively small amount of PACAP, conceivably involved in the regulation of folliculogenesis. PACAP is synthesized as a preprohormone and is processed by prohormone convertases, such as PC1, PC2, and PC4. PC4 is expressed only in the testis and ovary, where neither PC1 nor PC2 is expressed. However, whether PC4 is the sole endoprotease for the PACAP precursor in the gonads remains unknown. Recent studies using PC4-transgenic mice revealed that male PC4-null mice exhibited severely impaired fertility, although spermatogenesis appeared to be normal. The female PC4-null mice exhibited delayed folliculogenesis in the ovaries. To examine whether PC4 is the sole processing enzyme for the PACAP precursor in the gonads, we analyzed testicular and ovarian extracts from the PC4-null and wild-type mice for PACAP (PACAP38 and PACAP27) and its messenger RNA using reverse phase HPLC combined with specific RIAs and ribonuclease protection assay, respectively. For RIAs, three different polyclonal antisera with different recognition sites were used to identify PACAP38, PACAP27, and its precursor. Neither the testis nor the ovary from the PC4-null mice expressed PACAP38 or PACAP27, but the levels of PACAP transcripts in the testis and ovary of homozygous PC4-deficient mice were considerably elevated compared with those of the wild-type and heterozygous animals. The findings indicate that PC4 is the sole processing enzyme for the precursor of PACAP in the testis and ovary of mice. The possibility that the absence of bioactive PACAP in the testis and ovary of PC4-null mice caused severely impaired fertility in the males and delayed folliculogenesis in females warrants investigation.
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