NDUFAF4 is located on the q arm of chromosome 6 in position 16.1 and has 3 exons.[1] The NDUFAF4 gene produces a 23.7 kDa protein composed of 203 amino acids.[6][7] HRPAP20 is a phosphoprotein, containing a phosphate group attachment and, potentially, multiple kinase recognition sequences. Additionally, it has a CaM-binding sequence that allows it to interact with calmodulin (CaM), which itself is involved in numerous cellular processes.[5]
Function
NADH:ubiquinone oxidoreductase (complex I) catalyzes the transfer of electrons from NADH to ubiquinone (coenzyme Q) in the first step of the mitochondrial respiratory chain, resulting in the translocation of protons across the inner mitochondrial membrane. NDUFAF4 encodes a complex I assembly factor that is important for the correct assembly and function of complex I.[1] NDUFAF4 colocalizes, comigrates to several assembly intermediates, and is codependent with NDUFAF3 from the early to late stages of complex I assembly. In addition to their close interactions with each other, NDUFAF4 and NDUFAF3 interact with NDUFS2, NDUFS3, NDUFS8, and NDUFA5 in a translation-dependent early assembly mechanism.[8] NDUFAF4 has also been shown to play a role in growth and apoptosis regulation through a CaM-mediated mechanism involving MMP-9 secretion.[5]
Clinical Significance
Mutations in NDUFAF4 (HRPAP20) have been associated with mitochondrial complex I deficiency,[1] infantile mitochondrial encephalomyopathy.[4] Additionally, research analyzing HRPAP20's effect on human cancer cells have suggested that it plays a role in tumor metastasis, malignant progression, and breast cancer.[5]
HRPAP20 was found to be significantly elevated in patient breast tumors as compared to normal tissue. Further analysis using tumor cell lines with constitutively expressed HRPAP20 suggests that it increases the invasiveness, proliferation, and apoptotic suppression of breast cancer cells. This is often indicative of tumor metastasis and malignant progression.[5]
Interactions
NDUFAF4 (HRPAP20) has been shown to interact closely with NDUFAF3 as well as with NDUFS2, NDUFS3, NDUFS8, and NDUFA5 in the mitochondrial inner membrane.[8] HRPAP20 also interacts with calmodulin (CaM) in a mechanism that results in increased MMP-9 secretion, associated with increased invasiveness in breast cancer cells.[5] In addition to co-complexes, NDUFAF4 has protein-protein interactions with WDR26.[10]
↑Donald Voet; Judith G. Voet; Charlotte W. Pratt (2013). "18". Fundamentals of biochemistry : life at the molecular level (4th ed.). Hoboken, NJ: Wiley. pp. 581–620. ISBN9780470547847.
↑ 5.05.15.25.35.45.5Karp CM, Shukla MN, Buckley DJ, Buckley AR (March 2007). "HRPAP20: a novel calmodulin-binding protein that increases breast cancer cell invasion". Oncogene. 26 (12): 1780–8. doi:10.1038/sj.onc.1209980. PMID17001319.
Karp CM, Shukla MN, Buckley DJ, Buckley AR (March 2007). "HRPAP20: a novel calmodulin-binding protein that increases breast cancer cell invasion". Oncogene. 26 (12): 1780–8. doi:10.1038/sj.onc.1209980. PMID17001319.
Tozlu-Kara S, Roux V, Andrieu C, Vendrell J, Vacher S, Lazar V, Spyratos F, Tubiana-Hulin M, Cohen P, Dessen P, Lidereau R, Bièche I (October 2007). "Oligonucleotide microarray analysis of estrogen receptor alpha-positive postmenopausal breast carcinomas: identification of HRPAP20 and TIMELESS as outstanding candidate markers to predict the response to tamoxifen". Journal of Molecular Endocrinology. 39 (4): 305–18. doi:10.1677/JME-07-0001. PMID17909269.