Disease relevance of AKAP4

• Sixty SCID and 60 nude mice for each of three human tumor cell lines (HGL9, HSTS26, HCT15) and for each of five murine cell lines (FSC1, FSC2, FSM1, FSM2, E01) and 60 SCID and 60 C3H mice for the FSa2 spontaneous C3H sarcoma were studied [1].
• To summarize the recent findings in our laboratory, proteins p82 and p86 have been isolated and apparently purified from MC-induced sarcomas and from an SV40-induced sarcoma of BALB/c mice [2].
• The plasmid subclones from phage lambda84 have been analyzed for bent DNA and one of these, p82, contains bent DNA and overlaps with the region of highest potential helical instability [3].
• OBJECTIVE: To determine whether mutations in the pro-hAKAP82 gene and the resulting pro-hAKAP82 and hAKAP82 proteins were associated with the infertility seen in a patient with stump tail sperm [4].
• The inability of the chondrosarcoma cell line FSCP-1 to maintain an adequate matrix turnover as well as a notable proliferative activity is similar to neoplastic chondrosarcoma in vivo [5].

High impact information on AKAP4

• More than 60 phosphorylated sequences were then mapped by MS/MS, including precise sites of tyrosine and serine phosphorylation of the sperm tail proteins AKAP-3 and AKAP-4 [6].
• Immunological studies substantiate that p82 is a naturally existing p72 variant and that both proteins are expressed at similar concentrations. p82 purified from HeLa cells is an ATP-dependent RNA helicase with biochemical properties almost identical to those of p72 [7].
• Ala- and Val-scanning mutagenesis determined that hydrophobic amino acids at three homologous positions are required for binding of RIalpha to FSC1/AKAP82 domain B and RIIalpha to AKAP Ht31 [8].
• An X-linked gene encodes a major human sperm fibrous sheath protein, hAKAP82. Genomic organization, protein kinase A-RII binding, and distribution of the precursor in the sperm tail [9].
• Although pro-mAKAP82 localizes only to the proximal portion of the principal piece of the flagellum, pro-hAKAP82 localized to the entire length of the principal piece [9].

Biological context of AKAP4

• Yeast two-hybrid assays and deletion mutagenesis were used to identify AKAP4-binding proteins and to map the binding regions on AKAP4 and on the proteins identified [10].
• Molecular genetic analysis of two human sperm fibrous sheath proteins, AKAP4 and AKAP3, in men with dysplasia of the fibrous sheath [11].
• These studies suggest several roles for hAKAP82 in sperm motility, including the regulation of signal transduction pathways [9].
• The pro-hAKAP82 gene mapped to human chromosome Xp11.2, indicating that defects in this gene are maternally inherited [9].
• Alternative splicing occurred in both the mouse and human pro-AKAP82 genes that resulted in at least two distinct transcripts and possibly two different proteins [9].

Anatomical context of AKAP4

• The AKAP4 precursor is processed in the flagellum and only the mature form of AKAP4 appears to bind AKAP3 [10].
• However, AKAP4 is synthesized and incorporated into the nascent fibrous sheath late in spermatid development [10].
• Immunostaining of AKAP4 protein was negative in sperm tails [12].
• RESULTS: Sp17 is present in the head and tail of spermatozoa, in the tail it is in the fibrous sheath, which contains AKAP3 and AKAP4 [13].
• CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that equine AKAP4 anchors PK-A to the spermatozoal flagellum (where the kinase is likely to be required for the regulation of spermatozoal motility), but decreases in spermatozoal motility in cooled or cryopreserved semen are not associated with decreased binding of AKAP4 and PK-A [14].

Associations of AKAP4 with chemical compounds

• Cyclic AMP-dependent protein kinases are secured within specific cytoplasmic domains by A-kinase anchoring proteins (AKAPs), and the most abundant protein in the fibrous sheath is AKAP4 [10].
• Inhibitors of serine/threonine kinases, including 6-DMAP, staurosporine, and H7 inhibited p82 phosphorylation, whereas inhibitors of tyrosine kinases, protein kinase C, cAMP-dependent protein kinase, and p70s6k did not prevent this modification [15].
• In addition, both pro-hAKAP82 and hAKAP82 are tyrosine phosphorylated in a capacitation-dependent manner [16].
• A prominent 82 kDa protein that was pS and pT-phosphorylated in immotile and motile sperm is likely the fibrous sheath component AKAP82 that is phosphorylated during spermatogenesis [17].

Other interactions of AKAP4

• These results suggest that AKAP3 is involved in organizing the basic structure of the fibrous sheath, whereas AKAP4 has a major role in completing fibrous sheath assembly [10].
• In 11 of 12 DFS patients, polymerase chain reaction for detecting the presence of partial sequence of AKAP4/AKAP3 binding regions gave positive results [18].

Analytical, diagnostic and therapeutic context of AKAP4

• No quantitative or qualitative differences between patients with DFS and normal controls were detected when sperm proteins were analyzed by either silver staining or immunoblot analysis using antibodies raised against AKAP4 and AKAP3 [11].
• Immunofluorescence staining of A-kinase anchoring protein 4 (AKAP4) showed a moderate and diffuse signal, revealing a disorganized and incompletely assembled fibrous sheath [18].
• OBJECTIVE: To determine whether a homologue of A-kinase anchor protein 4 (AKAP4) is present and functional as an AKAP in equine spermatozoa and examine the effect of semen cooling and cryopreservation on binding of equine AKAP4 to the regulatory (RII) subunit of protein kinase-A (PK-A) [14].
• PCR analysis revealed intragenic deletions of the Akap3 and Akap4 genes [12].
• We report the case of an infertile man with normal sperm count and total sperm immotility in which dysplasia of the fibrous sheath, Akap3, Akap4 gene deletions, meiotic segregation of chromosomes 18, X and Y and Y microdeletions were investigated [12].

References