Multi-tasking role of the mechanosensing protein Ankrd2 in the signaling network of striated muscle.
BACKGROUND
Ankrd2 (also known as Arpp) together with Ankrd1/CARP and DARP are members of the MARP mechanosensing proteins that form a complex with titin (N2A)/calpain 3 protease/myopalladin. In muscle, Ankrd2 is located in the I-band of the sarcomere and moves to the nucleus of adjacent myofibers on muscle injury. In myoblasts it is predominantly in the nucleus and on differentiation shifts from the nucleus to the cytoplasm. In agreement with its role as a sensor it interacts both with sarcomeric proteins and transcription factors.


RESULTS
Expression profiling of endogenous Ankrd2 silenced in human myotubes was undertaken to elucidate its role as an intermediary in cell signaling pathways. Silencing Ankrd2 expression altered the expression of genes involved in both intercellular communication (cytokine-cytokine receptor interaction, endocytosis, focal adhesion, tight junction, gap junction and regulation of the actin cytoskeleton) and intracellular communication (calcium, insulin, MAPK, p53, TGF-β and Wnt signaling). The significance of Ankrd2 in cell signaling was strengthened by the fact that we were able to show for the first time that Nkx2.5 and p53 are upstream effectors of the Ankrd2 gene and that Ankrd1/CARP, another MARP member, can modulate the transcriptional ability of MyoD on the Ankrd2 promoter. Another novel finding was the interaction between Ankrd2 and proteins with PDZ and SH3 domains, further supporting its role in signaling. It is noteworthy that we demonstrated that transcription factors PAX6, LHX2, NFIL3 and MECP2, were able to bind both the Ankrd2 protein and its promoter indicating the presence of a regulatory feedback loop mechanism.


CONCLUSIONS
In conclusion we demonstrate that Ankrd2 is a potent regulator in muscle cells affecting a multitude of pathways and processes.
Muscle Molecular Biology Group, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
Anna
A
Belgrano
Ljiljana
L
Rakicevic
Lorenza
L
Mittempergher
Stefano
S
Campanaro
Valentina C
VC
Martinelli
Vincent
V
Mouly
Giorgio
G
Valle
Snezana
S
Kojic
Georgine
G
Faulkner
D000818:Animals; D002460:Cell Line; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D040542:Mechanotransduction, Cellular; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D009124:Muscle Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D054792:Muscle, Striated / Q000166:cytology* / Q000378:metabolism*; D017570:MyoD Protein / Q000378:metabolism; D009687:Nuclear Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D054731:PDZ Domains; D011401:Promoter Regions, Genetic / Q000235:genetics; D034622:RNA Interference; D012097:Repressor Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D059467:Transcriptome; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D018909:src Homology Domains
C491304:ANKRD1 protein, human; C432364:ANKRD2 protein, human; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; D009124:Muscle Proteins; D017570:MyoD Protein; C095552:NKX2-5 protein, human; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53