Disease relevance of AHNAK

• We next characterized AHNAK as a major Ca(2+)-dependent S100B target protein in the rat glial C6 and human U-87MG astrocytoma cell lines [1].
• AHNAK is expressed by means of a 17.5-kilobase mRNA in diverse cellular lineages but is typically repressed in cell lines derived from human neuroblastomas and in several other types of tumors [2].

High impact information on AHNAK

• In contrast, the other enlargeosome marker, desmoyokin/Ahnak, is transported across the organelle membrane, apparently by an ABC transporter, and binds to its lumenal face [3].
• Protein kinase B phosphorylates AHNAK and regulates its subcellular localization [4].
• AHNAK is a ubiquitously expressed giant phosphoprotein that was initially identified as a gene product subject to transcriptional repression in neuroblastoma [4].
• In this study we show that the extranuclear localization of AHNAK in epithelial cells depends on the formation of cell-cell contacts [4].
• Identification of an AHNAK Binding Motif Specific for the Annexin2/S100A10 Tetramer [5].

Biological context of AHNAK

• The giant protein AHNAK is a specific target for the calcium- and zinc-binding S100B protein: potential implications for Ca2+ homeostasis regulation by S100B [1].
• Interestingly, although some AHNAK antibodies stain interphase nuclei, no evidence of mitotic spindle localization is seen, suggesting that the identity of the protein at the latter location is more closely related to titin than AHNAK [6].
• Using a panel of somatic cell hybrids, we have mapped the locus for the AHNAK/desmoyokin gene (AHNAK) to human chromosome 11 [7].
• We show that AHNAK is a phosphorylation substrate of protein kinase B (PKB) in vitro and in vivo [4].
• It is surprising that amino acid sequence analysis of pig pp700 revealed homology to AHNAK-encoded protein, which was originally identified in human cell lines of neural crest origin as 700-kDa phosphoprotein [8].

Anatomical context of AHNAK

• In an attempt to define the molecular basis of the S100B action, we have identified the giant phosphoprotein AHNAK as the major and most specific Ca(2+)-dependent S100B target protein in rat embryo fibroblast cells [1].
• Whereas desmoyokin/AHNAK protein is distributed in the nucleus and cytoplasm in nonepithelial tissues, it is distributed in the cell membrane in epithelial tissues [9].
• Desmoyokin/AHNAK protein localizes to the non-desmosomal keratinocyte cell surface of human epidermis [10].
• The carboxyl-terminal region of ahnak provides a link between cardiac L-type Ca2+ channels and the actin-based cytoskeleton [11].
• Confocal microscopy of human left ventricular tissue localized the carboxyl-terminal ahnak portion to the sarcolemma including the T-tubular system and the intercalated disks of cardiomyocytes [11].

Associations of AHNAK with chemical compounds

• The calcium-induced phosphorylation of the desmoyokin/AHNAK protein was confirmed by immunoprecipitation using [32P]orthophosphate-labeled keratinocytes [12].

Physical interactions of AHNAK

• AHNAK binds to S100B-Sepharose beads and is also recovered in anti-S100B immunoprecipitates in a strict Ca(2+)- and Zn(2+)-dependent manner [1].
• We show that AHNAK has weak DNA-binding activity and forms a stable complex with the DNA ligase IV-XRCC4 complex on DNA [13].

Regulatory relationships of AHNAK

• We characterised AHNAK as a protein that stimulates the double-stranded (DS) ligation activity of DNA ligase IV-XRCC4 [13].

Other interactions of AHNAK

• Furthermore, AHNAK and the DNA ligase IV-XRCC4 complex co-immunoprecipitate demonstrating an in vivo interaction [13].
• Multiple antibodies to titin immunoreact with AHNAK and localize to the mitotic spindle machinery [6].
• Here, we showed using a yeast triple-hybrid experiment and in vitro binding assay that Annexin2 is required for strong binding of S100A10 to the C-terminal domain of the protein Ahnak [5].
• In a recent study, we demonstrated the association of ahnak with the regulatory beta2 subunit of the cardiac L-type Ca2+ channel [11].
• TPA also induced translocation of both the desmoyokin/AHNAK protein and desmoplakin, which was completely inhibited by PKC inhibitors [12].

Analytical, diagnostic and therapeutic context of AHNAK

• Sequencing of peptide fragments of the immunopurified protein reveals identity to AHNAK, a nuclear phosphoprotein, an identification that was confirmed by Western blot analysis with antibodies to AHNAK and peptide fragmentation patterns [6].
• Sequence-directed antibodies raised against human AHNAK recognized pp700 in immunoblotting and immunoprecipitation experiments, confirming the homology between both proteins [8].
• Cardiac AHNAK expression was assessed on mRNA level by reverse transcriptase-polymerase chain reaction [8].
• Localization of the human AHNAK/desmoyokin gene (AHNAK) to chromosome band 11q12 by somatic cell hybrid analysis and fluorescence in situ hybridization [7].
• Post-embedding immunoelectron microscopy with cryofixation and cryosubstitution revealed that desmoyokin was localized mainly along the non-desmosomal and non-hemidesmosomal plasma membrane, but not to the desmosomes and hemidesmosomes themselves [10].

References