Dermatology: Practical and Conceptual Original Article | Dermatol Pract Concept. 2025;15(4):5679 1 Differential Expression of Claudin-3 and Claudin-1 in Mycosis Fungoides: Implications for Disease Monitoring Akın Aktaş1,2, Funda Erduran2, Burcu Tuğrul3, Funda Eren4, Esra Fırat Oğuz5 1 Department of Dermatology, Ankara Yıldırım Beyazıt University, Ankara, Turkey 2 Department of Dermatology, Ankara Bilkent City Hospital, Ankara, Turkey 3 Private Dermatology Clinic, Ankara, Turkey 4 Department of Biochemistry, İstanbul Başakşehir Çam and Sakura City Hospital, İstanbul, Turkey 5 Department of Biochemistry, Ankara Bilkent City Hospital, Ankara, Turkey Key words: Mycosis Fungoides, Claudin-1, Claudin-3, Disease Monitoring, Biomarker Citation: Aktaş A, Erduran F, Tuğrul B, Eren F, Fırat Oğuz E. Differential Expression of Claudin-3 and Claudin-1 in Mycosis Fungoides: Implications for Disease Monitoring. Dermatol Pract Concept. 2025;15(4):5679. DOI: https://doi.org/10.5826/dpc.1504a5679 Accepted: June 28, 2025; Published: October 2025 Copyright: ©2025 Aktaş et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Introduction: Claudins are integral transmembrane proteins that play a pivotal role in regulating tight junctions within epithelial and endothelial cells. In addition to their fundamental function in preserv- ing cell-cell adhesion and barrier integrity, claudins are implicated in various biological processes, including those critical to cancer development and dermatological disorders. However, the role of claudin-1 and claudin-3 in mycosis fungoides (MF) pathogenesis remains unexplored and has yet to be comprehensively studied. Objectives: This study aimed to investigate the serum levels of claudin-1 and claudin-3 in MF patients and assess their potential clinical significance as biomarkers for disease progression. Methods: A total of 88 MF patients and 88 healthy controls were included in this case-control study. Serum claudin-1 and claudin-3 levels were measured using enzyme-linked immunosorbent assay (ELISA). Statistical analyses were performed to compare claudin levels between groups and examine correlations with disease stage and duration. Results: Serum claudin-3 levels were significantly higher in MF patients compared to controls (P<0.001), while no significant difference was observed in claudin-1 levels (P=0.448). Additionally, a weak but statistically significant positive correlation was found between claudin-3 levels and MF stage (r=0.219, P=0.041), suggesting its potential role in disease progression. No significant correlation was observed between claudin-1 levels and MF stage. ABSTRACT 2 Original Article | Dermatol Pract Concept. 2025;15(4):5679 Corresponding Author: Funda Erduran, Ankara Bilkent City Hospital, Department of Dermatology, Ankara, Turkey. ORCID: 0000-0002-3318-2248. Email: fnderdrn@gmail.com Introduction Claudins are integral membrane proteins that play a crucial role in the formation and function of tight junctions, which are essential to maintaining the integrity of epithelial and endothe- lial cell layers. They regulate paracellular permeability and are involved in various cellular processes, including growth and adhesion [1-3]. In recent years, these proteins have garnered significant attention and have been implicated in a variety of diseases [1,4]. Alterations in claudin expression have been im- plicated also in various malignancies, influencing tumor behav- ior, including proliferation, invasion, and metastasis [5]. Mycosis fungoides (MF) is the most common type of cu- taneous T-cell lymphoma, characterized by the proliferation of malignant T lymphocytes in the skin. The pathogenesis of MF involves complex interactions between malignant cells and the skin microenvironment, leading to the disruption of normal skin architecture and function [6]. Among the claudin family, claudin-1 and claudin-3 have been identified as significant contributors to the structural and functional properties of the skin [1]. However, the spe- cific roles of claudin-1 and claudin-3 in the pathogenesis of MF remain underexplored. Claudin-1 is a critical compo- nent of the skin's barrier function. Studies have shown that claudin-1-deficient mice experience significant water loss due to impaired tight junctions in the epidermis, highlighting its importance in maintaining skin integrity [7]. In the con- text of MF, although disruptions in skin barrier function are not directly studied, alterations in claudin expression could contribute to such barrier defects. Research on various skin cancers has demonstrated changes in claudin expression [8,9]. A previous study showed that claudins 1, 2, 3, 4, 5, and 7 exhibit distinct expression patterns in solar keratosis and cutaneous squamous cell carcinoma, supporting their involvement in the progression from premalignant to ma- lignant lesions [10] Although MF is a distinct entity, these findings can imply that claudins may influence the behavior of skin malignancies. Understanding the expression patterns of these proteins in MF could provide valuable insights into the mechanisms underlying the disease and may offer potential biomarkers for diagnosis and prognosis. Furthermore, monitoring serum claudin levels during treatment may provide insights into treatment efficacy and potential resistance mechanisms [4]. Objectives Our study aimed to investigate the serum levels of claudin-1 and claudin-3 in patients with MF and to assess their poten- tial clinical significance in the context of MF. Methods Ethical Approval and Study Design Prior to the study, ethical approval was obtained from the Ankara Bilkent City Hospital Ethics Committee on 4 Sep- tember 2024, under protocol number TABED 2-24-453. The study included 88 patients diagnosed with MF, and 88 age- and sex-matched healthy controls. All participants provided informed consent before the study. Data collected from pa- tients included age, sex, disease duration, and disease stage. Inclusion and Exclusion Criteria for the Participants Participants aged 18 and over were included in the study. Ex- clusion criteria for the participants included individuals with inflammatory bowel disease, those who had experienced acute or chronic gastrointestinal infections within the three months preceding the study, individuals who had undergone any gastrointestinal surgery within the six months prior, un- explained weight loss, nonsteroidal anti-inflammatory drug use within the week before the study, individuals on a diet regimen, use of antibiotics, probiotics, or synbiotics within the three months prior, a history of malignancy, alcohol de- pendence, and/or chronic liver and pancreatic diseases; preg- nant and breastfeeding females were also excluded. Peripheral venous blood samples were collected after a 12-hour fasting period. After a 2-hour clotting period in se- rum separation tubes, samples were centrifuged at 1000×g for 20 minutes. The resulting serum aliquots were stored at −80° C until further analysis. The concentrations of target proteins in the test sam- ples were estimated based on previous studies [11], and an Conclusion: Our findings indicate that elevated serum claudin-3 levels are associated with MF and correlate with disease severity, suggesting that claudin-3 may serve as a valuable biomarker for mon- itoring disease progression. Further research is required to elucidate its underlying mechanisms and assess its potential as a therapeutic target in MF. Original Article | Dermatol Pract Concept. 2025;15(4):5679 3 appropriate dilution factor was selected to ensure that the diluted target protein concentrations fell within the optimal detection range of the kit. Concentrations read from the standard curve were multiplied by the dilution factor. All measurements were performed in accordance with the man- ufacturer's instructions. To measure serum claudin-1 and claudin-3 levels (ng/ml), commercially available enzyme-linked immunosorbent assay (ELISA) kits from Elabscience, Texas, USA, were utilized. The kits used were: • Claudin-1 (Catalog No: E-EL-H0745; Lot No: WP- 24FHJ89507; Detection Range: 0.16–10 ng/ml; Sensitiv- ity: 0.09 ng/ml) • Claudin-3 (Catalog No: E-EL-H0754; Lot No: WP2346048679; Detection Range: 0.31–20 ng/ml; Sen- sitivity: 0.19 ng/ml) Each measurement was performed in duplicate, and the average values were used for further analysis. For the afore- mentioned ELISA analyses, intra-assay and inter-assay coef- ficient of variation (CV) values were found to be below 10%. Statistical Analysis Data analysis was conducted using SPSS 11.5 software. De- scriptive statistics for quantitative variables are reported as mean ± standard deviation and median (minimum-maximum), while qualitative variables are described by frequency (percentage). To assess the differences between two categories of a qualitative variable concerning quantitative variables, the Student's t-test was used if the normality assumption was met, and the Mann-Whitney U test was employed if normality was not assumed. To examine the relationship be- tween two quantitative variables, the Spearman correlation test was used, as the normality assumption was not satisfied. The chi-square test was applied to assess the relationship be- tween two qualitative variables. The statistical significance level was set at 0.05. Results Among the participants, 88 (50.0%) were diagnosed with MF, and 88 (50.0%) were in the control group. The aver- age age of the patients with MF was 50.95 ± 13.98 years, whereas the average age of the control group was 52.39 ± 12.73 years. The mean age at disease onset and disease du- ration in MF patients were 41.97 ± 13.43 years and 8.85 ± 10.43 years, respectively. Regarding the disease stage, 38 (43.2%) patients were in stage 1A, 30 (34.1%) in stage 1B, 13 (14.8%) in stage 2A, five (5.7%) in stage 2B, one (1.1%) in stage 3A, and one (1.1%) in stage 4A. The mean claudin-1 and claudin-3 values for the participants were 13.45 ± 3.65 ng/mL and 1064.56 ± 261.71 ng/mL, respec- tively (Table 1). There was no significant difference between the two groups in terms of sex and age (P=0.227 and P=0.079, Table 1. Descriptors of Demographic Data. Variables Descriptive Statistics Group, N (%) MF 88 (50.0) Control 88 (50.0) Sex, N (%) Female 84 (47.7) Male 92 (52.3) Age at disease onset (year) Mean±SD 41.97±13.43 Median (Min-Max) 43.00 (10.00-75.00) Disease duration (year) Mean±SD 8.85±10.43 Median (Min-Max) 5.00 (0.50-78.00) MF stage, N (%) 1A 38 (43.2) 1B 30 (34.1) 2A 13 (14.8) 2B 5 (5.7) 3A 1 (1.1) 4A 1 (1.1) Claudin-1 (ng/mL) Mean±SD 13.45±3.65 Median (Min-Max) 13.78 (4.85-23.80) Claudin-3 (ng/mL) Mean±SD 1064.56±261.71 Median (Min-Max) 1037.26 (524.78-1724.92) Abbreviations: SD: standard deviation, Min: minimum, Max: maximum, MF: Mycosis fungoide 4 Original Article | Dermatol Pract Concept. 2025;15(4):5679 remains controversial. In some cancers, reduced claudin-1 expression has been associated with enhanced tumor inva- sion and progression, whereas in others, its loss has been linked to improved patient outcomes [1,3,4,12]. In breast cancer, the expression of claudin-1 varies across patholog- ical subtypes, with downregulation frequently associated with increased invasiveness and poor prognosis. Conversely, elevated claudin-1 expression has been observed in certain basal-like breast cancer subtypes [13]. Similarly, in esopha- geal squamous cell carcinoma, reduced claudin-7 expression is associated with enhanced invasiveness and metastatic po- tential , highlighting the complex role of claudins in cancer biology [14]. Claudin-3, primarily expressed in the epidermis and other epithelial tissues, plays a key role in regulating the permeability of tight junctions. Interestingly, both down- regulation and upregulation of claudin-3 can contribute to tumor progression in a tumor-type-dependent manner [15]. In urothelial carcinomas, a strong correlation has been ob- served between claudin-3 upregulation and tumor grade and stage progression, aligning with findings from Nakanishi et al., who reported a link between high claudin-3 expression and advanced stage, high grade, and poor overall survival in a cohort of 129 upper urinary tract urothelial cancers [16]. In colorectal adenocarcinoma, nuclear localization of claudin-3 has been linked to tumor progression [17]. respectively). However, a significant difference was found between the two groups regarding claudin-3 levels (P=0.079 and P<0.001, respectively). The mean claudin-3 (ng/mL) level was significantly higher in the MF group compared to the control group. Table 2 presents the comparisons of vari- ables between the MF and control groups. No significant correlation was found between MF stage and claudin-1 levels, whereas a weak but statistically signif- icant positive correlation was observed between claudin-3 levels and MF stage (r=0.219, P=0.041). As the stage of MF increased, claudin-3 levels also increased. Table 3 examines the relationship between claudin levels and the stage of MF. No significant correlation was found between clau- din levels and either disease duration or disease onset age (P>0.05). Table 4 examines the relationship between claudin levels and disease duration and disease onset age. Discussion The current study focused on evaluating serum claudin-1 and claudin-3 levels in patients with MF and their poten- tial role as biomarkers for disease progression. Our findings demonstrate that serum claudin-3 levels were significantly elevated in the MF group compared to controls. Moreover, serum claudin-3 levels showed a positive correlation with disease stage, suggesting its involvement in the pathophys- iology and progression of MF. In contrast, serum claudin-1 levels did not differ significantly between MF patients and controls, nor did it correlate with disease stage. These results suggest that claudin-3 may serve as a valuable biomarker for disease monitoring in MF, while claudin-1 appears to have limited utility in this context. Alterations in claudin expression have been extensively documented in various malignancies. For instance, claudin-1 is one of the most widely studied claudins in cancer re- search, but its role as either a tumor promoter or suppressor Table 2. Comparisons of Variables between MF and Control groups. Variables MF Control p-value Age (year) Mean±SD 50.95±13.98 52.39±12.73 0.079a (Min-Max) (18.00-82.00) (30.00-83.00) Sex, N (%) Female 38 (43.2) 46 (52.3) 0.227c Male 50 (56.8) 42 (47.7) Claudin-1 (ng/mL) Mean±SD 13.66±3.73 13.24±3.58 0.448a Median (Min-Max) 13.77 (4.85-21,40) 13.78 (6,33.23,80) Claudin-3 (ng/mL) Mean±SD 1223.45±226.09 905.67±188.65 <0.001b Median (Min-Max) 1202.35 (687.09-1724.92) 877.50 (524.78-1613.26) Abbreviations: SD: standard deviation Min: minimum, Max: maximum, a: Student's t-test b: Mann-Whitney U test c: chi-square test, MF: Mycosis fungoides. Table 3. The Relationship between Claudin Levels and MF Stages. Claudin Level MF stage Claudin-1 (ng/mL) Correlation Coefficient −0.002 p value 0.982a Claudin-3 (ng/mL) Correlation Coefficient 0.219 p value 0.041a a: Spearman correlation test, MF: Mycosis fungoides Original Article | Dermatol Pract Concept. 2025;15(4):5679 5 Conclusions In conclusion, this study provides compelling evidence that serum claudin-3 levels are significantly elevated in MF pa- tients and correlate positively with disease stage. These find- ings suggest that claudin-3 may serve as a useful biomarker for assessing disease progression in MF. Further research is warranted to elucidate the precise role of claudin-3 in the pathogenesis of MF and to investigate its potential as a ther- apeutic target in this and other malignancies. References 1. Bhat AA, Syed N, Therachiyil L, et al. Claudin-1, A Double-Edged Sword in Cancer. Int J Mol Sci. 2020;21(2):569. DOI: 10.3390 /ijms21020569. PMID: 31952355; PMCID: PMC7013445. 2. Hewitt KJ, Agarwal R, Morin PJ. The claudin gene family: Expression in normal and neoplastic tissues. BMC Cancer. 2006;6:186. DOI: 10.1186/1471-2407-6-186. 2006;6:186. DOI: 10.1186/1471-2407-6-186. PMID: 16836752; PMCID: PMC1538620. 3. Tao D, Guan B, Li H, Zhou C. Expression patterns of claudins in cancer. Heliyon. 2023;9(11):e21338. DOI: 10.1016/j.heli- yon.2023.e21338. PMID: 37954388; PMCID: PMC10637965. 4. Hana C, Thaw Dar NN, Galo Venegas M, Vulfovich M. Clau- dins in Cancer: A Current and Future Therapeutic Target. Int J Mol Sci. 2024;25:4634. DOI: 10.3390/ijms25094634. PMID: 38731853; PMCID: PMC11083183. 5. Ding L, Lu Z, Lu Q, Chen YH. The claudin family of proteins in human malignancy: a clinical perspective. Cancer Manag Res. 2013;5:367-75. DOI: 10.2147/CMAR.S38294. PMID: 24232410; PMCID: PMC3825674. 6. Jawed SI, Myskowski PL, Horwitz S, Moskowitz A, Querfeld C. Primary cutaneous T-cell lymphoma (mycosis fungoides and Sézary syndrome): part I. Diagnosis: clinical and histopathologic features and new molecular and biologic markers. J Am Acad Dermatol. 2014;70(2):205.e1-16; quiz 221-2. DOI: 10.1016/j. jaad.2013.07.049. PMID: 24438969. 7. Proksch E, Brandner JM, Jensen JM. The skin: an indispens- able barrier. Exp Dermatol. 2008;17(12):1063-72. DOI: 10 .1111/j.1600-0625.2008.00786.x. PMID: 19043850. 8. French AD, Fiori JL, Camilli TC, et al. Pkc and pka phosphoryla- tion affect the subcellular localization of claudin-1 in melanoma cells. Int J Med Sci 2009;6:93–101. DOI: 10.7150/ijms.6.93 9. Sappayatosok K., Phattarataratip E. Overexpression of claudin-1 is associated with advanced clinical stage and invasive pathologic In the context of MF, its overexpression may suggest ei- ther a compensatory response or a pathogenic factor con- tributing to disease progression. Elevated claudin-3 levels could enhance tumor development by strengthening cell-cell adhesion, facilitating the accumulation of malignant cells, or promoting the epithelial-to-mesenchymal transition, a crucial process in cancer metastasis [15]. We think the el- evated claudin-3 expression observed in the current study may contribute to disease progression by enhancing tumor cell proliferation and invasiveness. The positive correlation between claudin-3 levels and disease stage further supports its potential role in MF advancement. The role of claudin-3 as a biomarker extends to derma- tology beyond oncology. Increased serum claudin-3 levels have been reported in psoriasis patients, indicating impaired intestinal permeability. This dysfunction suggests a potential avenue for therapeutic intervention by targeting the intesti- nal barrier [18]. Furthermore, claudin-1 has been evaluated as a potential biomarker in psoriasis, with reduced levels ob- served in specific subtypes and correlated with disease onset [19]. In another study, alterations in claudin expression were observed in chronic plaque psoriasis, with claudin-1 being absent in the epidermis of psoriatic plaques, while typical staining patterns are present in clinically normal skin [20]. These studies emphasize the diverse roles of claudins in vari- ous diseases and their potential as therapeutic targets. To the best of our knowledge, there is a lack of studies in the current literature specifically assessing serum claudin-1 and claudin-3 levels in patients with MF or other cutaneous lymphomas. Our study contributes to this growing body of evidence by establishing a significant association between el- evated serum claudin-3 levels and disease severity in MF. The findings align with prior research highlighting the involve- ment of tight junction proteins in cancer progression. While no significant association was identified between claudin lev- els and disease duration or age at onset, these findings may be influenced by the limited sample size of the study. Larger cohorts and longitudinal studies are needed to validate these results and explore the potential mechanistic pathways link- ing claudin-3 to MF pathogenesis. Table 4. The Relationship between Claudin Levels, Disease Duration, and Age at Disease Onset. Claudin Level Disease duration (year) Disease onset - age (year) Claudin-1 (ng/mL) Correlation Coefficient 0.032 0.187 p-value 0.768a 0.081a Claudin-3 (ng/mL) Correlation Coefficient 0.113 −0.095 p-value 0.293a 0.381a a: Spearman correlation test 6 Original Article | Dermatol Pract Concept. 2025;15(4):5679 cell carcinoma of the esophagus. Hum Pathol. 2006;37(5):569-77. DOI: 10.1016/j.humpath.2005.12.018. PMID: 16647955. 15. Büyücek S, Schraps N, Menz A, et al. Prevalence and clinical significance of Claudin-3 expression in cancer: a tissue mi- croarray study on 14,966 tumor samples. Biomark Res. 2024;12(1):154. DOI: 10.1186/s40364-024-00702-w. PMID: 39658782; PMCID: PMC11633013. 16. Nakanishi K, Ogata S, Hiroi S, Tominaga S, Aida S, Kawai T. Expression of occludin and claudins 1, 3, 4, and 7 in urothelial carcinoma of the upper urinary tract. Am J Clin Pathol.2008;130(1):43-9. DOI: 10.1309/U77A6BTEXV- CA5D0E. PMID: 18550469. 17. Tokuhara Y, Morinishi T, Matsunaga T, et al. Nuclear expres- sion of claudin-3 in human colorectal adenocarcinoma cell lines and tissues. Oncol Lett. 2018;15(1):99-108. DOI: 10.3892 /ol.2017.7281. Epub 2017 Oct 26. PMID: 29285188; PMCID: PMC5738677. 18. Mahran A, Hosni AM, Farag NG, Elkhawaga AA, Mageed AAA. Role of Claudin- 3 as a biomarker of gut-skin axis integrity in characteristics of oral squamous cell carcinoma. Head Neck Pathol. 2015;9:173–80. DOI: 10.1007/s12105-014-0559-z. PMID: 25078758; PMCID: PMC4424206. 10. Hintsala HR, Siponen M, Haapasaari KM, Karihtala P, Soini Y. Claudins 1, 2, 3, 4, 5 and 7 in solar keratosis and squamocellular carcinoma of the skin. Int J Clin Exp Pathol. 2013;6(12):2855-63. PMID: 24294371; PMCID: PMC3843265. 11. Stec A, Maciejewska M, Zaremba M, et al. The Clinical Signifi- cance of Serum Biomarkers of the Intestinal Barrier in Systemic Sclerosis: A Cross-Sectional Study. J Pers Med. 2023;13(4):678. DOI: 10.3390/jpm13040678. PMID: 37109064; PMCID: 12. Li J. Dysregulated expression of claudins in cancer. Oncol Lett. 2021;22(3):641. DOI: 10.3892/ol.2021.12902. Epub 2021 Jul 7. PMID: 34386063; PMCID: PMC8298996. 13. Wang DW, Zhang WH, Danil G, Yang K, Hu JK. The role and mechanism of claudins in cancer. Front Oncol. 2022;12:1051497. DOI: 10.3389/fonc.2022.1051497. PMID: 36620607; PMCID: PMC9818346. 14. Usami Y, Chiba H, Nakayama F, et al. Reduced expression of claudin-7 correlates with invasion and metastasis in squamous Original Article | Dermatol Pract Concept. 2025;15(4):5679 7 patients with psoriasis. Arch Dermatol Res. 2024;316(7):476. DOI: 10.1007/s00403-024-03071-4. PMID: 39023797. 19. Xu L, Pan Y, Tang S, et al. Evaluation of Serum Proinflamma- tory Cytokine IL-17A and Tight Junction Protein Claudin-1 in Psoriasis. Contrast Media Mol Imaging. 2022;2022:6092808. DOI: 10.1155/2022/6092808. PMID: 35340911; PMCID: PMC8920681. 20. Watson RE, Poddar R, Walker JM, et al. Altered claudin ex- pression is a feature of chronic plaque psoriasis. J Pathol. 2007;212(4):450-8. DOI: 10.1002/path.2200. PMID: 17582238.