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PubMed2001

alpha-Adducin gene and essential hypertension in China.

Adducin is a membrane skeletal protein that is involved in the regulation of membrane ion transport and cellular signal transduction. Essential hypertension has been linked to alpha-adducin gene locus, and association of a polymorphism of the gene has been found in some studies, but results of linkage or association studies on alpha-adducin gene are controversial among different populations. This study was designed to examine the linkage between alpha-adducin gene locus and essential hypertension and to reveal the relationship between an alpha-adducin gene polymorphism (Gly460Trp) and essential hypertension in a Chinese population. For the linkage study, one hundred and six Chinese nuclear families were recruited, including 417 hypertensive patients in all 474 individuals. Those samples were genotyped at D4S412 and D4S3038. The distances between the two microsatellite markers and the alpha-adducin gene locus are less than 3cM. Parametric, non-parametric linkage (NPL) analyses using the GENEHUNTER software were carried out. Sib transmission-dise- quilibrium test (S-TDT), as well as transmission-disequilibrium test (TDT). was also implemented with TDT/S-TDT Program 1.1. Serum levels of uric acid, creatinine, blood urea nitrogen (BUN), fasting glucose and lipids were determined as phenotypes. In an association study, 138 hypertensive and 121 normotensive subjects were genotyped at Gly460Trp of the alpha-adducin gene to examine a possible association between this polymorphism and blood pressure or other phenotypes. We fail to find the linkage between the two markers and essential hypertension by parametric, NPL analysis or TDT/S-TDT study. With the use of the simple association and the multivariate logistic regression analyses, we also fail to reveal a significant association between the Gly460Trp polymorphism in alpha-adducin gene and the blood pressure variation, or blood biochemical indices studied. The frequency of the 460Trp allele in Chinese (46-48%) is similar to that found in Japanese (54-60%) while the allele frequency is less common in Caucasian (13%-23%). These findings suggest that in our Chinese population, alpha-adducin 460Trp variant may not play an important role in the etiology of EH. And the negative results of linkage and TDT/ S-TDT further supports this conclusion.

Adult↗
PubMed1999

Phosphorylation of adducin by Rho-kinase plays a crucial role in cell motility.

Adducin is a membrane skeletal protein that binds to actin filaments (F-actin) and thereby promotes the association of spectrin with F-actin to form a spectrin-actin meshwork beneath plasma membranes such as ruffling membranes. Rho-associated kinase (Rho- kinase), which is activated by the small guanosine triphosphatase Rho, phosphorylates alpha-adducin and thereby enhances the F-actin-binding activity of alpha-adducin in vitro. Here we identified the sites of phosphorylation of alpha-adducin by Rho-kinase as Thr445 and Thr480. We prepared antibody that specifically recognized alpha-adducin phosphorylated at Thr445, and found by use of this antibody that Rho-kinase phosphorylated alpha-adducin at Thr445 in COS7 cells in a Rho-dependent manner. Phosphorylated alpha-adducin accumulated in the membrane ruffling area of Madin-Darby canine kidney (MDCK) epithelial cells and the leading edge of scattering cells during the action of tetradecanoylphorbol-13-acetate (TPA) or hepatocyte growth factor (HGF). The microinjection of Botulinum C3 ADP-ribosyl-transferase, dominant negative Rho-kinase, or alpha-adducinT445A,T480A (substitution of Thr445 and Thr480 by Ala) inhibited the TPA-induced membrane ruffling in MDCK cells and wound-induced migration in NRK49F cells. alpha-AdducinT445D,T480D (substitution of Thr445 and Thr480 by Asp), but not alpha-adducinT445A,T480A, counteracted the inhibitory effect of the dominant negative Rho-kinase on the TPA-induced membrane ruffling in MDCK cells. Taken together, these results indicate that Rho-kinase phosphorylates alpha-adducin downstream of Rho in vivo, and that the phosphorylation of adducin by Rho-kinase plays a crucial role in the regulation of membrane ruffling and cell motility.

Amino Acid Sequence↗
PubMed2000

Hypertension in beta-adducin-deficient mice.

Polymorphic variants of the cytoskeletal protein adducin have been associated with hypertension in humans and rats. However, the direct role of this protein in modulating arterial blood pressure has never been demonstrated. To assess the effect of beta-adducin on blood pressure, a beta-adducin-deficient mouse strain (-/-) was studied and compared with wild-type controls (+/+). Aortic blood pressure was measured in nonanesthetized, freely moving animals with the use of telemetry implants. It is important to note that these mice have at least 98% of C57Bl/6 genetic background, with the only difference from wild-type animals being the beta-adducin mutation. We found statistically significant higher levels of systolic blood pressure (mm Hg) (mean+/-SE values: -/-: 126.94+/-1.14, n=5; +/+: 108.06+/-2. 34, n=6; P:</=0.0001), diastolic blood pressure (-/-: 83.54+/-1.07; +/+: 74.87+/-2.23; P:</=0.005), and pulse blood pressure (-/-: 43. 32+/-1.10; +/+: 33.19+/-1.96; P:</=0.001) in beta-adducin-deficient mice. Western blot analysis showed that as a result of the introduced genetic modification, beta-adducin was not present in heart protein extracts from -/- mice. Consequently, this deficiency produced a sharp decrease of alpha-adducin and a lesser reduction in gamma-adducin levels. However, we found neither cardiac remodeling nor modification of the heart function in these animals. This is the first report showing direct evidence that hypertension is triggered by a mutation in the adducin gene family.

Animals↗
PubMed2005

Impaired synaptic plasticity and learning in mice lacking beta-adducin, an actin-regulating protein.

The adducin family of proteins interacts with the actin cytoskeleton and the plasma membrane in a calcium- and cAMP-dependent manner. Thus, adducins may be involved in changes in cytoskeletal organization resulting from synaptic stimulation. beta-Adducin knock-out mice were examined in physiological and behavioral paradigms related to synaptic plasticity to elucidate the role the adducin family plays in processes underlying learning and memory. In situ hybridization for alpha- and beta-adducin demonstrates that these mRNAs are found throughout the brain, with high levels of expression in the hippocampus. Schaffer collateral-CA1 tetanic long-term potentiation decayed rapidly in acute hippocampal slices from beta-adducin knock-out mice, although baseline spine morphology and postsynaptic density were normal. Interestingly, the input-output relationship was significantly increased in hippocampal slices from beta-adducin knock-out mice. Furthermore, beta-adducin knock-out mice were impaired in performance of fear conditioning and the water maze paradigm. The current results indicate that beta-adducin may play an important role in the cellular mechanisms underlying activity-dependent synaptic plasticity associated with learning and memory.

Actins↗
PubMed2000

Adducin: structure, function and regulation.

Adducin is a ubiquitously expressed membrane-skeletal protein localized at spectrin-actin junctions that binds calmodulin and is an in vivo substrate for protein kinase C (PKC) and Rho-associated kinase. Adducin is a tetramer comprised of either alpha/beta or alpha/gamma heterodimers. Adducin subunits are related in sequence and all contain an N-terminal globular head domain, a neck domain and a C-terminal protease-sensitive tail domain. The tail domains of all adducin subunits end with a highly conserved 22-residue myristoylated alanine-rich C kinase substrate (MARCKS)-related domain that has homology to MARCKS protein. Adducin caps the fast-growing ends of actin filaments and also preferentially recruits spectrin to the ends of filaments. Both the neck and the MARCKS-related domains are required for these activities. The neck domain self-associates to form oligomers. The MARCKS-related domain binds calmodulin and contains the major phosphorylation site for PKC. Calmodulin, gelsolin and phosphorylation by the kinase inhibit in vitro activities of adducin involving actin and spectrin. Recent observations suggest a role for adducin in cell motility, and as a target for regulation by Rho-dependent and Ca2+-dependent pathways. Prominent physiological sites of regulation of adducin include dendritic spines of hippocampal neurons, platelets and growth cones of axons.

Actins↗
PubMed1995

Spatial and sub-cellular localization of the membrane cytoskeleton-associated protein alpha-adducin in the rat brain.

Studies on the identification and characterization of constituents of rat brain synaptic junctions have lead to the isolation of cDNA clones encoding segments of alpha-adducin. These and other studies suggest that adducin, a protein involved in promoting the assembly of actin and spectrin filaments at the plasma membrane, may play a role in dynamic assembly-disassembly processes underlying synaptic plasticity. In order to verify that brain alpha-adducin is indeed a constituent of synaptic structures, we have generated monoclonal antibodies against epitopes in the C-terminal region of alpha-adducin and have determined its spatial and sub-cellular distribution in postnatal day-30 rat brain. Alpha-adducin is found to be highly enriched in regions with high synapse densities of the hippocampus, corpus striatum, cerebral cortex and cerebellum. Immuno-electron microscopic analysis of peroxidase stained sections of the hippocampus and the cerebellum revealed that alpha-adducin is localized at distinct sub-cellular structures. In the CA1 and CA3 regions of the hippocampus alpha-adducin immunoreactivity is found in a distinct subset of dendrites and dendritic spines. In the molecular layer of the cerebellum, a distinct fraction of pre-synaptic terminals of parallel fiber terminals is labeled. In both cases the majority of synaptic structures does not contain adducin. Significant immunoreactivity is also detected in processes of glial cells both in the hippocampus and the cerebellum.

Animals↗
PubMed2005

Rho-kinase induces association of adducin with the cytoskeleton in platelet activation.

We examined whether adducin function is regulated through Rho-kinase after agonist stimulation in platelets. A variety of stimuli such as thrombin, STA(2) (a stable analog of TXA(2)), Ca(2+) ionophore, phorbol diester, and shear stress induced phosphorylation of alpha-adducin at Thr445. Preincubation with the Rho-kinase inhibitor Y-27632 in platelets inhibited agonist-induced phosphorylation of alpha-adducin. STA(2) stimulation led to a redistribution of adducin from Triton-insoluble (high speed) fraction (membrane skeleton) to Triton-insoluble (low speed) fraction (cytoskeleton) and detergent-soluble fraction. Phosphoadducin at Thr445 was selectively isolated in the cytoskeletal fraction, whereas phosphoadducin at Ser726 was mainly present in the Triton-soluble fraction. Y-27632 inhibition of STA(2)-induced alpha-adducin phosphorylation at Thr445 inhibited incorporation of alpha-adducin and spectrin into the platelet cytoskeleton, although Y-27632 did not affect phosphorylation of alpha-adducin at Ser726. These results suggest that Rho-kinase regulates the association of alpha-adducin and spectrin with the actin cytoskeleton in platelet activation.

Blood Platelets↗
PubMed2001

Association of protein kinase C(lambda) with adducin in 3T3-L1 adipocytes.

There is evidence that the atypical protein kinases C (PKC(lambda), PKC(zeta)) participate in signaling from the insulin receptor to cause the translocation of glucose transporters from an intracellular location to the plasma membrane in adipocytes. In order to search for downstream effectors of these PKCs, we identified the proteins that were immunoprecipitated by an antibody against PKC(lambda/zeta) from lysates of 3T3-L1 adipocytes through peptide sequencing by mass spectrometry. The data show that PKC(lambda) is the major atypical PKC in these cells. Moreover, an oligomeric complex consisting of alpha- and gamma-adducin, which are cytoskeletal proteins, coimmunoprecipitated with PKC(lambda). Association of the adducins with PKC(lambda) was further indicated by the finding that the adducins coimmunoprecipitated proportionally with PKC(lambda) in repeated rounds of immunoprecipitation. Such an association is consistent with literature reports that the adducins contain a single major site for PKC phosphorylation in their carboxy termini. Using antibody against the phospho form of this site for immunoblotting, we found that insulin caused little or no increase in the phosphorylation of this site on the adducins in a whole cell lysate or on the small portion of the adducins that coimmunoprecipitated with PKC(lambda). PKC(lambda) and the adducins were located in both the cytosol and subcellular membranous fractions. The binding of PKC(lambda) to adducin may function to localize PKC(lambda) in 3T3-L1 adipocytes.

3T3 Cells↗
PubMed1998

No association between alpha-adducin 460 polymorphism and essential hypertension in a Japanese population.

Many unknown genetic factors are involved in the pathogenesis of hypertension. Recently, the reverse genetic approach revealed that some genetic variants, such as angiotensinogen, lipoprotein lipase, and alpha-adducin gene polymorphisms, increase the risk for hypertension. Both in rat and human, the genetic predisposition to hypertension was confirmed only for angiotensinogen and alpha-adducin genes. Adducin is a membrane cytoskeletal protein, which is thought to regulate sodium transport. Abnormalities of membrane sodium transport in the kidney play an important role in hypertension. A recent report by Cusi et al showed that the Trp allele of alpha-adducin polymorphism (Gly 460 Trp) is associated with an increased risk of hypertension in whites, which led us to carry out a case-control study to examine whether the same association is observed in the Japanese population. We recruited 170 hypertensive and 194 normotensive Japanese subjects and compared the genotype distribution of alpha-adducin 460 polymorphism between cases and controls and between whites and Japanese. Trp allele frequency of controls in the Japanese subjects was twice as high as in the whites. However, no association was observed between alpha-adducin polymorphism and hypertension. Furthermore, alpha-adducin 460 polymorphism was not associated with any clinical characteristics. Accordingly, we concluded that alpha-adducin 460 polymorphism is not a major genetic risk for hypertension in Japanese people.

Alleles↗
PubMed1996

A new function for adducin. Calcium/calmodulin-regulated capping of the barbed ends of actin filaments.

Adducin is a membrane skeleton protein originally described in human erythrocytes that promotes the binding of spectrin to actin and also binds directly to actin and bundles actin filaments. Adducin is associated with regions of cell-cell contact in nonerythroid cells, where it is believed to play a role in regulating the assembly of the spectrin-actin membrane skeleton. In this study we demonstrate a novel function for adducin; it completely blocks elongation and depolymerization at the barbed (fast growing) ends of actin filaments, thus functioning as a barbed end capping protein (Kcap approximately 100 nM). This barbed end capping activity requires the intact adducin molecule and is not provided by the NH2-terminal globular head domains alone nor by the COOH-terminal extended tail domains, which were previously shown to contain the spectrin-actin binding, calmodulin binding, and phosphorylation sites. A novel difference between adducin and other previously described capping proteins is that it is down-regulated by calmodulin in the presence of calcium. The association of stoichiometric amounts of adducin with the short erythrocyte actin filaments in the membrane skeleton indicates that adducin could be the functional barbed end capper in erythrocytes and play a role in restricting actin filament length. Our experiments also suggest novel possibilities for calcium regulation of actin filament assembly by adducin in erythrocytes and at cell-cell contact sites in nonerythroid cells.

Actin Cytoskeleton↗
PubMed1999

Linkage but lack of association for blood pressure and the alpha-adducin locus in normotensive twins.

BACKGROUND: alpha-adducin is a cytoskeletal protein involved with sodium-pump activity in the renal tubule. The alpha-adducin gene locus has been linked to hypertension and a polymorphism identified which is associated with hypertension; however, the role of the alpha-adducin gene locus in normal blood pressure regulation is not defined. We performed a combined linkage and association study in normotensive monozygotic (MZ) and dizygotic (DZ) twins and their parents to address this issue. METHODS: We studied 126 MZ and 70 DZ twin pairs and parents of DZ twins. Blood pressure values and responses to a cold pressor test were obtained. Cardiac dimensions were measured echocardiographically. Three microsatellites adjacent to the alpha-adducin gene were studied as well as the 460 Trp mutation in the alpha-adducin gene. RESULTS: We obtained strong evidence for linkage (P< 0.001) between the alpha-adducin gene locus and systolic blood pressure. However, we were not able to associate the 460 Trp mutation with higher blood pressures, cold pressor responses or cardiac dimensions. CONCLUSIONS: The alpha-adducin gene locus is relevant to blood pressure regulation in normal subjects. Failure to find an association between higher blood pressures and the 460 Trp mutation suggests that this mutation may become important only when hypertension is triggered, or that other variations in alpha-adducin are present which have not yet been discovered.

Adolescent↗
PubMed2003

Alpha-adducin gene polymorphism is associated with essential hypertension in Chinese: a case-control and family-based study.

OBJECTIVE: A polymorphism at position 460(G <-- W) of the alpha-adducin gene was found to be associated with essential hypertension in some but not all studies. The aim of the present study was to further investigate the association of the alpha-adducin 460W allele with essential hypertension in Chinese population. METHODS: Individuals from a population-based sample (n = 748) and 95 nuclear families and 47 discordant sibships were studied by questionnaire as well as by physical examination and biochemical analyses. The alpha-adducin gene G460W polymorphism was determined by polymerase chain reaction and restriction enzyme digestion. Chi-square test, one-way analysis of variance, logistic regression, linear regression, haplotype-based haplotype relative risk and transmission/disequilibrium test analyses were used to determine the association between the alpha-adducin G460W polymorphism and essential hypertension. RESULTS: In the case-control study, the prevalence of hypertension was higher in individuals with the WW genotype (40.0%) as compared with those with the GW and GG genotype (31.7%) (chi2 = 4.768, P = 0.029, odds ratio = 1.43). Adjusted for the conventional risk factors of hypertension, alpha-adducin polymorphism still plays an independent role on systolic blood pressure. We confirmed the results of our case-control study by observing a significant preferential transmission of the 460W allele of the alpha-adducin to the affected subjects in another northern Chinese population (for haplotype-based haplotype relative risk, chi2 = 6.24, P = 0.01; and for the transmission/disequilibrium test, chi2 = 4.69, P = 0.03). CONCLUSIONS: The present findings show a positive association between the alpha-adducin G460W polymorphism and essential hypertension in a northern Chinese population. This evidence indicates that the alpha-adducin gene may be a susceptible gene to essential hypertension.

Adult↗
PubMed1996

Hypertension-associated point mutations in the adducin alpha and beta subunits affect actin cytoskeleton and ion transport.

The adducin heterodimer is a protein affecting the assembly of the actin-based cytoskeleton. Point mutations in rat adducin alpha (F316Y) and beta (Q529R) subunits are involved in a form of rat primary hypertension (MHS) associated with faster kidney tubular ion transport. A role for adducin in human primary hypertension has also been suggested. By studying the interaction of actin with purified normal and mutated adducin in a cell-free system and the actin assembly in rat kidney epithelial cells (NRK-52E) transfected with mutated rat adducin cDNA, we show that the adducin isoforms differentially modulate: (a) actin assembly both in a cell-free system and within transfected cells; (b) topography of alpha V integrin together with focal contact proteins; and (c) Na-K pump activity at V(max) (faster with the mutated isoforms, 1281 +/- 90 vs 841 +/- 30 nmol K/h.mg pt., P < 0.0001). This co-modulation suggests a role for adducin in the constitutive capacity of the epithelia both to transport ions and to expose adhesion molecules. These findings may also lead to the understanding of the relation between adducin polymorphism and blood pressure and to the development of new approaches to the study of hypertension-associated organ damage.

Actins↗
PubMed1998

Redistribution and enhanced protein kinase C-mediated phosphorylation of alpha- and gamma-adducin during renal tumor progression.

Tumor promotion/progression is known to be due in part to increased signaling through a variety of mitogenic pathways, including protein kinase C (PKC). To determine whether increased PKC activity could play a role in promotion and progression of renal cancer, we monitored PKC activity in normal and progressively transformed renal neoplasias from Eker rats. Eker rats carry a defect in the tumor suppressor TSC2 gene that predisposes them to renal carcinoma, whereas additional factors influence tumor promotion/progression in accordance with a "two-hit" model. We used the phosphorylation of adducins at Ser-660, a known PKC phosphorylation site, as a reporter for endogenous PKC activity. In normal proximal tubules, total adducin levels (measured with a phosphorylation state-insensitive antibody) were relatively high, whereas pSer660-adducin (measured with a phosphorylation state-sensitive antibody) levels were very low. In comparison, in renal carcinomas, total adducin levels were decreased, and pSer-660-adducin levels were increased. Changes in phosphorylation correlated with changes in localization. In normal tissue, alpha- and gamma-adducin are targeted to the apical and basal membranes of proximal tubules, respectively, implying unique functions for these related proteins. In early lesions (atypical tubules), differential targeting is lost, and both alpha- and gamma-adducins localize to the basal membrane. In more advanced lesions, staining in lateral membranes at cell-cell contacts becomes apparent. Furthermore, in cells that have lost basement membrane contact, plasma membrane targeting is no longer apparent. These changes in adducin expression levels, phosphorylation state, and localization parallel the increased growth potential and dedifferentiation of the progressive tumor phenotypes. These data demonstrate the utility of phosphorylation state-selective antibodies in immunohistochemical applications as reporters of endogenous PKC activity in tissue samples. We also provide the first evidence that increased PKC activity and phosphorylation of important target proteins occurs during progressive transformation in a non-phorbol ester tumor promotion model in vivo.

Animals↗
PubMed1995

Genomic organization of the human alpha-adducin gene and its alternately spliced isoforms.

The cDNA for the human alpha-adducin gene has been cloned, and different alternately spliced forms have been identified. We report the complete genomic organization of the human alpha-adducin gene and these alternately spliced forms. The human alpha-adducin gene, spanning approximately 85 kb, consists of 16 exons ranging in size from 34 to 1892 bp. One of the spliced forms of the human alpha-adducin gene results from alternate use of the 5' splice donor site for exon 10, while another results in a truncated protein following insertion of 34 bp comprising exon 15, followed by a premature stop codon. This alternate spliced form of alpha-adducin is predicted to result in an altered carboxyl terminus that would eliminate a protein kinase and calmodulin binding site. Seven nucleotide substitutions and 4 insertion/deletions were also identified. The 5' region of the human alpha-adducin gene contains one Sp1 site, two AP2 sites, and two CAAT boxes. No TATA box was apparent, consistent with features of a housekeeping gene. We have mapped another cDNA within the first intron of the human alpha-adducin gene, suggesting overlapping genes in this 4p16.3 genomic region.

Alternative Splicing↗
PubMed2005

Pleiotrophin stimulates tyrosine phosphorylation of beta-adducin through inactivation of the transmembrane receptor protein tyrosine phosphatase beta/zeta.

Pleiotrophin (PTN the protein, Ptn the gene) signals through a unique mechanism; it inactivates the tyrosine phosphatase activity of its receptor, the transmembrane receptor protein tyrosine phosphatase (RPTP)beta/zeta, and increases tyrosine phosphorylation of the substrates of RPTPbeta/zeta through the continued activity of a yet to be described protein tyrosine kinase(s) in PTN-stimulated cells. We have now found that the cytoskeletal protein beta-adducin interacts with the intracellular domain of RPTPbeta/zeta in a yeast two-hybrid system, that beta-adducin is a substrate of RPTPbeta/zeta, that beta-adducin is phosphorylated in tyrosine in cells not stimulated by PTN, and that tyrosine phosphorylation of beta-adducin is sharply increased in PTN-stimulated cells, suggesting that beta-adducin is a downstream target of and regulated by the PTN/RPTPbeta/zeta signaling pathway. beta-Catenin was the first downstream target of the PTN/RPTPbeta/zeta signaling pathway to be identified; these data thus also suggest that PTN coordinately regulates steady state levels of tyrosine phosphorylation of the important cytoskeletal proteins beta-adducin and beta-catenin and, through PTN-stimulated tyrosine phosphorylation, beta-adducin may contribute to the disruption of cytoskeletal structure, increased plasticity, and loss of homophilic cell-cell adhesion that are the consequences of PTN stimulation of cells and a characteristic feature of different malignant cells with mutations that activate constitutive expression of the endogenous Ptn gene.

Amino Acid Sequence↗
PubMed2001

Beta1 adducin gene expression in DRG is developmentally regulated and is upregulated by glial-derived neurotrophic factor and nerve growth factor.

Differential display technique has proven to be effective in identifying differentially regulated genes under a variety of experimental conditions. We identified beta1 adducin as a target in primary rat dorsal root ganglia (DRG) cultures that is upregulated by exposure to nerve growth factor (NGF) and glial-derived neurotrophic factor (GDNF). We used real-time reverse-transcription polymerase chain reaction (RT-PCR) for quantitative measurement of beta1 adducin gene expression both in DRG cultures and in vivo. Significant increase in beta1 adducin expression level was observed in DRG cultures treated with either GDNF or NGF, compared to untreated cultures. The expression of beta1 adducin in rat tissues was highest in the brain and high in the cerebellum, superior cervical ganglion and DRG tissues. By contrast, low expression levels of beta1 adducin are detected in sciatic nerve and in non-neural tissues. Our study also showed that expression of beta1 adducin gene is developmentally regulated in rat DRG and trigeminal ganglia, with a peak around P0 and significant attenuation by P21. The level of expression of beta1 adducin in adult rat DRG and trigeminal ganglia may be maintained by the action of neurotrophic factors that are produced in innervated targets like skin and muscle.

Animals↗
PubMed1993

Localization of adducin in epidermis.

On the cytoplasmic side of the plasma membrane of erythrocytes there is a dense protein filament matrix that maintains the shape of the cells. The main constituents of this system, actin and spectrin, which have also been detected in keratinocytes and fibroblasts, are known to be linked in erythrocytes in a network structure by additional proteins such as band 4.1 and adducin. The interaction between actin and spectrin, mediated by adducin, is regulated by calmodulin and protein kinase C. Because we have previously found adducin in cultured keratinocytes, we investigated epidermis by immunochemical techniques. We found adducin to be localized at cell-cell contact sites in epidermis using affinity-purified antibodies against human erythrocyte adducin. Immunofluorescence of epidermis revealed an intense fluorescence in the basal layer, whereas stratum spinosum and stratum granulosum showed moderate staining. There was intense staining at sites of cell-cell contact in cultured human keratinocytes. Immunoblot analysis indicated the presence of adducin polypeptides of 103 kd and 97 kd in epidermis, but in cultured keratinocytes only the higher molecular weight form could be detected. This study indicates adducin, a regulatory protein in erythrocytes, is also present in epidermis. Its localization suggests that it may be involved in the formation of the microfilament matrix of the membrane skeleton at cell-cell contact sites.

Actins↗