Disease relevance of ACTN4

• The human non-muscle alpha-actinin protein encoded by the ACTN4 gene suppresses tumorigenicity of human neuroblastoma cells [1].
• Mutations in the ACTN4 gene that encodes actinin 4 has also been associated with familial nephrotic syndrome [2].
• Mutations in podocyte proteins, such as nephrin, alpha-actinin 4, and podocin, are associated with proteinuria and nephrotic syndrome [3].
• The identification of an inactivating mutation in ACTN4 emphasizes its role as a tumor suppressor gene and underlines the involvement of cytoskeleton alteration in tumor development and metastasis [4].
• Biopsies from 83 patients with acquired proteinuric diseases were analyzed (minimal change disease [MCD; n = 13], benign nephrosclerosis [n = 16], membranous glomerulopathy [n = 31], focal and segmental glomerulosclerosis [FSGS; n = 9], and controls [n = 14]) [5].
• Actinin-4 contributes to the invasive growth of pancreatic ductal carcinoma, and ACTN4 is one of the candidate oncogenes in this chromosome locus [6].

High impact information on ACTN4

• Here we present evidence implicating mutations in the gene encoding alpha-actinin-4 (ACTN4; ref. 2), an actin-filament crosslinking protein, as the cause of disease in three families with an autosomal dominant form of FSGS [7].
• When injected into the mesocecum of severe combined immunodeficient mice, DLD1 Tet-off ACTN4 cells, but not the control cells, metastasized into regional mesenteric lymph nodes, resembling the behavior of clinical cancers [8].
• Upon the induction of actinin-4, DLD1 Tet-off ACTN-4 cells spread filopodia and significantly increased their motility ( P = .00027); actinin-4 protein was concentrated at the leading edges of these actin-rich podia [8].
• A colorectal cancer cell clone capable of inducing actinin-4 using the tetracycline-regulatory system (designated DLD1 Tet-off ACTN-4) was established [8].
• Thus, ACTN4 is a critical regulator of AKT1 localization and function [9].

Chemical compound and disease context of ACTN4

• Immunofluorescence showed colocalization of alpha-actinin-4 with ZO-1 in cultured HeLa and C6 glioma cells, as well as in a variety of tissues in vivo, including brain, heart, liver, and lung [10].
• By this criterion, nephrotic FSGS is usually steroid-resistant and, if not controlled by more aggressive therapy, typically progresses to ESRD [11].
• DESIGN: Eleven adult patients with biopsy-proven primary FSGS and nephrotic syndrome resistant to steroids and cytotoxic drugs were treated with plasmapheresis in addition to oral prednisolone and intravenous cyclophosphamide [12].
• FSGS was recurrent in 2/10 cFSGS cases compared with 8/19 ncFSGS (P = NS). cFSGS was associated with more proteinuria (11.9 vs 7.2 g/day, P = 0.05) and higher serum creatinine (4.2 vs 1.9 mg/dl, P = 0.0001) at diagnosis [13].
• The patient with steroid-responsive IgM nephrotic syndrome did not respond to cyclosporin, and there was no significant effect of cyclosporin on proteinuria in the four patients with FSGS [14].

Biological context of ACTN4

• We found a C to T transition at nucleotide 465 in the ACTN4 gene in all of patients, and a T to C transition at nucleotide 954 in exon eight of podocin gene in two of five patients, resulting in no amino acid substitutions [15].
• We respectively knockdown the nephrin, podocin, CD2AP, or alpha-actinin-4 mRNA by using reconstructed RNA interference vector--psiRNA-hH1GFPzeo in mouse podocyte clone [16].
• Interestingly, experiments using cell lines stably expressing ACTN4 demonstrated that as opposed to WT gene, mutant ACTN4 was unable to inhibit tumor cell growth in vitro and in vivo [4].
• We sequenced NPHS2 promoter region from -628 to ATG in a large cohort of 260 nephrotic patients (161 with FSGS) who were presenting proteinuria from moderate to severe and were receiving or had received modular therapies according to their sensitivity to steroids and other immune modulators [17].
• Consistent with human ACTN4-associated FSGS, which shows incomplete penetrance, a proportion of the transgenic mice exhibited significant albuminuria (8 of 18), while the overall average systolic BP was elevated in both proteinuric and non-proteinuric ACTN4-mutant mice [18].

Anatomical context of ACTN4

• Cell lines typically co-express ACTN4 and ACTN1, a second non-muscle alpha-actinin gene [1].
• Mutations in ACTN4, encoding alpha-actinin-4, cause an autosomal-dominant focal segmental glomerulosclerosis. alpha-actinin-4 stabilizes the podocyte cytoskeleton structure, connecting with actin filaments [19].
• To further assess the function of human ACTN4, we studied a lung carcinoma cell line expressing a mutated alpha-actinin-4, which is recognized as a tumor antigen by autologous CD8(+) cytotoxic T lymphocytes (CTL) [4].
• However, given ACTN4's known functions and the suspected functions of actin and actin-related proteins in chromatin remodeling and other nuclear events, ACTN4 may assist NF-Y in recruiting chromatin-remodeling complexes or may direct NF-Y/ACTN4-targeted genes to the nuclear matrix and active transcriptional complexes [20].
• T cell receptor (TCR) analysis revealed that alpha-actinin-4-reactive clones used distinct alpha and beta chain rearrangements, demonstrating TCR repertoire diversity [21].

Associations of ACTN4 with chemical compounds

• In addition, the expression marker was able to predict steroid responsiveness in diagnostically challenging cases of MCD versus FSGS (n = 6) [5].
• Overexpression of alpha-actinin-4 potentiates the inhibitory effect of ionomycin on NHE3 activity by accelerating the oligomerization and endocytosis of NHE3 [22].
• High glucose and advanced glycosylated end-products affect the expression of alpha-actinin-4 in glomerular epithelial cells [23].
• Renal alpha-actinin-4: purification and puromycin aminonucleoside-binding property [24].
• Consistent with integrin-dependent alpha-actinin-4-mediated adhesion, phosphorylation of beta1-integrins on alpha-actinin-4-deficient podocytes is reduced [25].

Physical interactions of ACTN4

• Here we report the identification of the alpha-subunit of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and alpha-actinin-4 as potential binding partners for the densin-180 intracellular segment [26].
• Screening of a human placenta cDNA library identified--in addition to the C-terminal region of cytokeratin 18 (CK18(182-430))--a large C-terminal fragment of alpha-actinin-4 (Act-4) as a binding partner for PAI-1 [27].

Co-localisations of ACTN4

• Exogenously expressed synaptopodin and alpha-actinin-4 were found to colocalize along with endogenous MAGI-1 at the tight junction of Madin-Darby canine kidney cells [28].

Regulatory relationships of ACTN4

• Attempts to demonstrate a role for NF-Y/ACTN4 in regulating CYP1A1 expression were unsuccessful, likely due to an inability to significantly change nuclear ACTN4 levels with phosphatidylinositol 3'-kinase agonists and antagonists [20].

Other interactions of ACTN4

• No ACTN4 or WT1 mutations were detected [19].
• CONCLUSIONS: In this study, we exhaustively analyzed the NPHS2 and the exon 8 of the ACTN4 genes in a series of sporadic 'adult-onset' FSGS patients [29].
• There are also 3 genetic loci connected with autosomal dominant forms of FSGS: ACTN4, TRPC6 and CD2AP (found only in the mice models) [30].
• In addition, this Ca(2+)-dependent inhibition requires Ca(2+)-dependent association between alpha-actinin-4 and E3KARP [22].
• Non-muscle alpha-actinin-4 interacts with plasminogen activator inhibitor type-1 (PAI-1) [27].

Analytical, diagnostic and therapeutic context of ACTN4

• The whole coding region, all intron/exon boundaries and flanking intronic regions of NPHS2 gene and the exon 8, i.e. hot-spot mutations of the ACTN4 gene, were analyzed in all patients by denaturing high-performance liquid chromatography (DHPLC) to search disease-causing defects [29].
• Electrophoretic mobility shift assays combined with Western blot analysis and co-immunoprecipitation experiments suggested that ACTN4 is associated with the NF-Y complex, but not NRF [20].
• Using small interfering RNA, chromatin immunoprecipitation, and transient transfection assays, we show that alpha-actinin 4 potentiates expression of TAF55, a putative MEF2 target gene [31].
• On the basis of a very small number of patients, it was suspected that children with homozygous or compound heterozygous mutations in NPHS2 might exhibit primary steroid resistance and a decreased risk of FSGS recurrence after kidney transplantation [32].
• Recently, genetic mapping of proteinuric kidney disease genes and animal models have revealed further important molecules for the kidney filtration function including alpha-actinin-4, podocin, FAT, and NEPH1 [33].

References