ANKRD2

Structure

Two isoforms of ARPP have been documented; a 39.8 kDa protein isoform composed of 360 amino acids and a 36.2 kDa protein isoform composed of 327 amino acids. ANKRD2 has nine exons, four of which encode ankyrin repeats in the middle region of the protein, a PEST-like and Lysine-rich sequence in the N-terminal region, and a Proline-rich sequence containing consensus sequences for phosphorylation in the C-terminal region. It has been proposed that ARPP can homo- or hetero-dimerize with other MARPs in an antiparallel fashion. ARPP is highly expressed in nuclei and I-bands in slow skeletal fibers and cardiac muscle, specifically in ventricular regions at intercalated discs; and expression in brain, pancreas and esophageal epithelium has also been documented. Though ARPP and CARP proteins show significant homology, their expression profiles in muscle cells are markedly different; CARP is expressed throughout atria and ventricles, in development and in adult myocytes, however ARPP is almost exclusively ventricular and only in adult myocytes. ARPP was also found to be expressed in rhabdomyosarcomas, exhibiting a pattern distinct from actin and desmin.

Function

ARPP localizes to both nuclei and sarcomeres in muscle cells. ARPP may play a role in the differentiation of myocytes, as ARPP expression was shown to be induced during the C2C12 differentiation in vitro. A role for ARPP in regulating muscle gene expression and sensing stress signals was implicated in the finding that ARPP colocalizes with the transcriptional co-activator and co-repressor PML in myoblast nuclei, and binds p53 to enhance the p21(WAFI/CIPI) promoter. It was further demonstrated that Nkx2.5 and p53 synergistically activate the ANKRD2 promoter to promote effects on myogenic differentiation. At the sarcomere, ARPP binds titin at I-bands, which is potentiated by homo-dimerization and can alter the protein kinase A/protein kinase C phosphorylation status of itself or titin. These studies demonstrate a stretch-responsive relationship between ARPP and Titin, which can be rapidly altered by post-translational mechanisms.

Functional insights into ARPP function have come from transgenic studies. In mice lacking all three muscle ankyrin repeat proteins (MARPs), ARPP, CARP, and DARP), skeletal muscles tended towards a more slower fiber type distribution, with longer resting sarcomere length, decreased fiber stiffness, expression of a longer titin isoform, greater degree of torque loss following eccentric contraction-related injury, and enhanced expression of MyoD and MLP. These findings suggest that ARPP and related MARP proteins may play a role in the passive stiffness and gene regulatory roles in skeletal muscle. A study investigating ARPP function in cardiac muscle in which ARPP was knocked out alone or in combination with the other MARPs showed that mice displayed normal cardiac function at baseline and in response to pressure overload-induced cardiac hypertrophy, suggesting that these proteins are not essential for normal cardiac development or in response to a hypertrophic stimulus.

ARPP has also shown to play a role in models of disease. ARPP has also exhibited elevated expression following skeletal muscle denervation, persisting for four weeks following the insult. ARPP (ANKRD2) gene expression was also shown to be rapidly induced in a model of eccentric contraction-related injury, showing peak expression (6-11 times normal value) within 12–24 hours following injury, suggesting that ARPP may play a role in repair. In a mouse model of muscular dystrophy with myositis (mdm) caused by a small deletion in titin, ANKRD2 mRNA expression was shown to be significantly elevated in skeletal muscle tissue along with that of CARP, suggesting a role for ARPP in titin-based signaling. Levels of ARPP were also altered in a mouse model of diabetes.

Clinical Significance

In patients with dilated cardiomyopathy, levels of ARPP were upregulated.

ARPP expression patterns have been shown to be altered in patients with amyotrophic lateral sclerosis (ALS), with decreased expression in slow skeletal muscle fibers and increased expression in fast skeletal muscle fibers.

ARPP has also been shown to be a potentially useful biomarker for the differential diagnosis between oncocytoma and chromophobe renal cell carcinomas.

In non-pathologic physiology, ARPP mRNA expression in skeletal muscle of patients was shown to be elevated two days following fatiguing jumping exercises. Levels of CARP, MLP and calpain-2 mRNA levels were also enhanced, suggesting that these molecules may be part of a signaling network activated by physical exercise.

Ankrd2 has been shown to be involved in the progression of some types of cancers, such as osteosarcoma and head and neck squamous cell carcinoma.

Interactions

ANKRD2 has been shown to interact with

• Titin
• YBX1,
• TCAP,
• PML and
• TP53.
• Lamin A and prelamin A
• Akt.

References

References

1. (Sep 2000). "Identification of Ankrd2, a novel skeletal muscle gene coding for a stretch-responsive ankyrin-repeat protein". Genomics.
2. (May 2004). "The Ankrd2 protein, a link between the sarcomere and the nucleus in skeletal muscle". J. Mol. Biol..
3. (May 2005). "Expression of Ankrd2 in fast and slow muscles and its response to stretch are consistent with a role in slow muscle function". J. Appl. Physiol..
4. "Entrez Gene: ANKRD2 ankyrin repeat domain 2 (stretch responsive muscle)".
5. (January 2021). "Ectopic Expression of Ankrd2 Affects Proliferation, Motility and Clonogenic Potential of Human Osteosarcoma Cells". Cancers.
6. (October 2020). "Epigenetic regulation of VENTXP1 suppresses tumor proliferation via miR-205-5p/ANKRD2/NF-kB signaling in head and neck squamous cell carcinoma". Cell Death & Disease.
7. "Protein sequence of human ANKRD2 (Uniprot ID: Q9GZV1)".
8. "Protein sequence of human ANKRD2 (Uniprot ID: Q9GZV1-2)".
9. (Jul 2001). "Characterization of human skeletal muscle Ankrd2". Biochemical and Biophysical Research Communications.
10. (Jul 2001). "Identification of a novel human ankyrin-repeated protein homologous to CARP". Biochemical and Biophysical Research Communications.
11. (Sep 2014). "Probing muscle ankyrin-repeat protein (MARP) structure and function". Anatomical Record.
12. (May 2002). "Arpp, a new homolog of carp, is preferentially expressed in type 1 skeletal muscle fibers and is markedly induced by denervation". Laboratory Investigation.
13. (Jun 2015). "Profiling of skeletal muscle Ankrd2 protein in human cardiac tissue and neonatal rat cardiomyocytes". Histochemistry and Cell Biology.
14. (Apr 2011). "Molecular characterization and different expression patterns of the muscle ankyrin repeat protein (MARP) family during porcine skeletal muscle development in vitro and in vivo". Animal Biotechnology.
15. (May 2002). "Carp, a cardiac ankyrin-repeated protein, and its new homologue, Arpp, are differentially expressed in heart, skeletal muscle, and rhabdomyosarcomas". The American Journal of Pathology.
16. (May 2004). "The Ankrd2 protein, a link between the sarcomere and the nucleus in skeletal muscle". Journal of Molecular Biology.
17. (Mar 2015). "Cardiac transcription factor Nkx2.5 interacts with p53 and modulates its activity". Archives of Biochemistry and Biophysics.
18. (Jul 2007). "Structural and regulatory roles of muscle ankyrin repeat protein family in skeletal muscle". American Journal of Physiology. Cell Physiology.
19. (2014). "The muscle ankyrin repeat proteins CARP, Ankrd2, and DARP are not essential for normal cardiac development and function at basal conditions and in response to pressure overload". PLOS ONE.
20. (Feb 2004). "Rapid muscle-specific gene expression changes after a single bout of eccentric contractions in the mouse". American Journal of Physiology. Cell Physiology.
21. (Feb 2004). "Induction and myofibrillar targeting of CARP, and suppression of the Nkx2.5 pathway in the MDM mouse with impaired titin-based signaling". Journal of Molecular Biology.
22. (Feb 2007). "Effects of streptozotocin-induced diabetes and physical training on gene expression of titin-based stretch-sensing complexes in mouse striated muscle". American Journal of Physiology. Endocrinology and Metabolism.
23. (Jul 2004). "Altered titin expression, myocardial stiffness, and left ventricular function in patients with dilated cardiomyopathy". Circulation.
24. (2002). "Altered expression of cardiac ankyrin repeat protein and its homologue, ankyrin repeat protein with PEST and proline-rich region, in atrophic muscles in amyotrophic lateral sclerosis". Pathobiology.
25. (Feb 2007). "ARPP protein is selectively expressed in renal oncocytoma, but rarely in renal cell carcinomas". Modern Pathology.
26. (Apr 2009). "Effects of fatiguing jumping exercise on mRNA expression of titin-complex proteins and calpains". Journal of Applied Physiology.
27. (Nov 2003). "The muscle ankyrin repeat proteins: CARP, ankrd2/Arpp and DARP as a family of titin filament-based stress response molecules". Journal of Molecular Biology.
28. PMID 28531892
29. (August 2011). "Ankrd2/ARPP is a novel Akt2 specific substrate and regulates myogenic differentiation upon cellular exposure to H(2)O(2)". Molecular Biology of the Cell.