Abstract 4635: Reg4-induced CD44ICD expression: A potential biomarker of human pancreatic cancer

Abstract Background and Aims: Regerating Gene 4 (Reg4) is highly upregulated in gastrointestinal (GI) malignancies including pancreatic cancers (PC). Numerous studies have demonstrated an association between higher Reg4 expression and PC tumor aggressiveness. However, the underlying mechanism remained unknown. Our recent studies identified CD44 intracytoplasmic domain (CD44ICD), a γ-secretase-mediated cleavage product of CD44, as a key downstream mediator of Reg4-signaling to activate genes involved in the regulation of cancer cell proliferation. We accordingly aimed this study to determine a link between Reg4/CD44ICD expression and PC patient survival and define its importance as an early biomarker for metastatic PC. Methods: A closed IRB-approved human study with PC patient linked survival and invasion data was used to construct 3 tissue microarray (TMA) slides of resected specimens. TMA slides were immunostained using Reg4-specific rabbit polyclonal and CD44ICD-specific goat polyclonal antibodies. Spearman’s correlation was used to study the association between individual proteins using percent mean expression (0-100%) and mean intensity (0, 1, 2, 3) as scored blindly by the pathologist. Product-limit survival estimates were obtained to estimate survival probability and log-rank tests were used to compare survival probability between groups. Patient-linked tumor grades were used to determine correlation between Reg4/CD44ICD expression and PC tumor grades. Results: Assessing immunostaining scores in PC specimens, cytoplasmic Reg4 (R2 = 0.121) and CD44ICD (R2 = 0.1168) expression along with nuclear expression of CD44ICD (R2 = 0.0261) showed a positive correlation with increasing PC grades. Analysis of product-limit survival estimates revealed that cytoplasmic expression of Reg4 and CD44ICD, and nuclear expression of CD44ICD in PC specimen was directly associated with poor patient survival irrespective of tumor grades. To determine the association of Reg4/CD44ICD expression with PC invasiveness, we extended our study and analyzed the patient linked lymphatic, venous and perinuclear invasion data. Following analysis, we observed almost universal presence of venous and perineural invasion in most of the PC patients without a direct correlation with cytoplasmic expression of Reg4 and CD44ICD, and nuclear expression of CD44ICD. However, we observed a significantly higher expression of nuclear CD44ICD in PC patients positive for lymphatic invasion, and data demonstrated a positive correlation between nuclear CD44ICD expression and lymphatic invasion (R2 = 0.0699). Conclusion: These results suggest that higher expression of Reg4 and CD44ICD constitute an important event responsible for poor survival of PC patients and identify CD44ICD as a key downstream mediator of Reg4 signaling, a potential therapeutic target and a critical biomarker of metastatic PC with lymphatic invasion. Citation Format: Tashvi Anand, Matthew A. Ciorba, Kumar S. Bishnupuri. Reg4-induced CD44ICD expression: A potential biomarker of human pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4635.