The Reg protein family: potential new targets for the treatment of inflammatory bowel disease and colorectal cancer.

Reg genes were first detected in pancreatic islet cells in 1988 ( 10 ). In rodents, the Reg protein family includes Reg1, Reg2, Reg3α, Reg3β, Reg3γ, Reg3δ, and Reg4, whereas in humans, it includes Reg1α, Reg1β, Reg3α, Reg3γ, and Reg4 ( 14 ). The Reg1 gene and its protein product are derived from pancreatic alveolar cells ( 15 ). Recent research has revealed an increase in the expression of Reg1 within the inflamed epithelial lining of the colon, potentially associated with the rejuvenation of colon mucosal cells and exhibiting anti-apoptotic properties ( 16 , 17 ). Reg1α was significantly upregulated in ulcerative colitis-associated colorectal cancer ( 18 ). The expression of the Reg2 gene is typically observed in pancreatic alveolar cells. In normal circumstances, it seems that the presence of Reg2 is not necessary for preserving pancreatic islet function and maintaining glucose balance. However, when confronted with aging or obesity induced by a high-fat diet, Reg2 plays a beneficial role in supporting the proliferation and functionality of pancreatic β cells. This ultimately aids in sustaining insulin secretion and promoting glucose homeostasis ( 19 ). Reg3 is an antimicrobial peptide expressed mainly in Paneth cells of the small intestine, which protects against bacteria and inhibits bacterial translocation, and Reg3 facilitates the maintenance of metabolic homeostasis in a variety of tissues and organs, such as the liver, intestines, and skin ( 20 ). Reg4 was first identified in high-throughput sequencing analysis of inflammatory bowel disease libraries, and its expression is associated with infection and inflammation, with pro-proliferative and anti-apoptotic effects in a number of gastrointestinal tumors, such as colorectal, hepatocellular, and gastric cancers ( 21 ,) ( 22 ).. In summary, the Reg protein family exhibits a close relationship with inflammation and cancer in the gastrointestinal tract, necessitating a comprehensive understanding of their role in inflammatory diseases. Consequently, targeting Reg proteins could potentially pave the way for novel therapeutic interventions.

Chronic inflammation of the gut in patients with IBD increases the risk of colorectal cancer, and patients with IBD accompanied by a long course and a wide range of lesions are at a considerably higher likelihood of developing colorectal cancer ( 52 ). A systematic review and meta-analysis revealed that the incidence of colorectal cancer in individuals diagnosed with UC was found to be 0.02% (95% CI 0.00–0.04) after a decade, 4.81% (3.26–6.36) after two decades, and 13.91% (7.09–20.72) after three decades ( 53 ). During the period of 1969–2017, a cohort study conducted in Sweden and Denmark, involving patients with IBD, revealed that individuals with Crohn’s disease had a 40% higher likelihood of developing concurrent colorectal cancer (CRC) compared to the general population ( 54 ). The pathogenic factors contributing to the development of colorectal cancer associated with inflammatory bowel disease encompass the extent and duration of chronic inflammation, genetic susceptibility, and the influence of symbiotic microbiota. Chronic inflammation induces oxidative stress-mediated DNA damage, thereby triggering oncogene activation and tumor suppressor gene inactivation ( 55 ). High expression of serum Reg1α in cancer patients was identified as an independent risk factor for cancer from an observational and cross-sectional study of 130 patients ( 56 ). Defective transduction of the p53 signaling pathway is an early event in the progression of developmental abnormalities to cancer. p53 immunohistochemistry can be used for the diagnosis of UC-associated colon cancer, and early mutations in P53 are detected in the intestinal mucosa of colorectal cancer patients ( 55 , 57 ). Immunohistochemical analysis of colectomy samples from 31 patients with long-term UC revealed that Reg1α was significantly elevated in ulcerative colitis-associated tumor tissues and was significantly and positively correlated with p53 expression ( 58 ). Knockout of the Reg1α gene significantly suppresses the viability of colorectal cancer cells and then induces apoptosis via modulation of the cyclin D1/CDK4 pathway and the BAX/BCL-2 pathway ( 59 ) ( Figure 3 ). The pro-proliferative and anti-apoptotic properties of Reg1α may contribute to the pathogenesis of colorectal cancer associated with inflammatory bowel disease. Reg1α may serve as a new biomarker for the diagnosis of colorectal cancer patients. Reg proteins promote or inhibit signaling pathways involved in the proliferation of colorectal cancer cells. The knockout of Reg1α gene significantly impeded the viability of colorectal cancer cells and induced apoptosis via modulation of the cyclin D1/CDK4 pathway and the BAX/BCL-2 pathway. Reg1α enhances the expression of the MYC gene in colorectal cancer by activating the Wnt/β-catenin signaling pathway, thereby promoting aerobic glycolysis in cancer cells through its interaction with LDHA. This metabolic alteration contributes to the proliferation and metastasis of colorectal cancer cells. The activation of the AKT and ERK1/2 pathways by Reg3α may contribute to the promotion of colorectal tumorigenesis. The inhibition of STAT3 by Reg3β can effectively impede the initiation and progression of colorectal cancer tumors. Reg4 promotes colorectal cancer cell proliferation and stem cell formation by interacting with the CD44 receptor and inducing its proteolysis, thereby increasing the expression of the CD44 intracytoplasmic domain (CD44ICD). Reg4 promotes colorectal cancer stem cell formation through the Wnt/β-catenin pathway. CRC, colorectal cancer; CD44ICD, CD44 intracytoplasmic domain; CDK4, cyclin-depend ent kinases4; LDHA, lactate dehydrogenase A. The primary energy source utilized by tumor cells is glycolysis, with aerobic glycolysis being recognized as an indicator of colorectal cancer ( 60 ). A recent study revealed that Reg1α enhances the expression of the oncogene MYC, which encodes a nucleoprotein, in colorectal cancer by activating the Wnt/β-catenin signaling pathway. Additionally, MYC forms a complex with lactate dehydrogenase A (LDHA) to promote aerobic glycolysis in cancer cells, thereby facilitating the proliferation and metastasis of colorectal cancer cells. Furthermore, elevated levels of Reg1α are indicative of an unfavorable prognosis for patients with colorectal cancer ( 61 ) ( Figure 3 ). In the future, targeting the Reg1α/β-catenin/MYC/LDHA pathway could be a viable therapy option for individuals with colorectal cancer. In addition to its involvement in the development of colorectal cancer, Reg1α also contributes to the treatment of this malignancy. The expression of Reg1α is upregulated in colorectal cancer cell lines, and genetic knockout of Reg1α has been shown to augment the sensitivity of these cells toward 5-fluorouracil (5-FU) chemotherapy ( 59 ). Reg3α is not only a promising tumor marker but also plays a key role in the development of gastrointestinal malignancies. Previous research indicates that Reg3α can promote cell proliferation and inhibit apoptosis, including regulating keratinocyte differentiation and proliferation in damaged skin tissues ( 62 , 63 ). Reg3α also functions as a growth factor that acts locally in hepatocytes, stimulating the proliferation and survival of these cells ( 64 ). In pancreatic cancer cells, Reg3a accelerates cell cycle progression by promoting the expression of cyclin D1 and enhances the expression of the anti-apoptotic gene Bcl2, and in pancreatic cancer cell lines SW1990 or BxPC-3, Reg3α promotes pancreatic cancer cell growth, proliferation, and tumor formation ( 65 , 66 ). Chen et al. ( 67 ) observed a significant upregulation of Reg3α mRNA levels in gastric cancer tissues, which subsequently facilitated the proliferation and migration of gastric cancer cells via activation of the JAK2/STAT3 signaling pathway. Therefore, based on the intrinsic pro-proliferative and anti-apoptotic activities of Reg3α, it can be speculated that overexpression of Reg3α in colorectal cancer can promote colorectal tumor growth. Earlier research has indicated that, in the presence of inflammation, Reg3α facilitates the proliferation of pancreatic cancer cells by activating the IL-6–JAK2/STAT3 signaling pathway ( 65 ). Elevated levels of IL-6 and sIL-6R are observed in the circulation and intestine of IBD patients, promoting colon cancer cell proliferation and tumor growth ( 68 ). Reg3α has been identified as a potential biomarker for the early detection of colorectal cancer, and Reg3α gene expression is upregulated in colorectal cancer tissues ( 69 ). Based on these findings, it is postulated that Reg3α may facilitate the initiation and progression of colorectal cancer in patients with IBD via activation of the IL-6–JAK2/STAT3 signaling pathway. In addition, Reg3α may promote colorectal tumorigenesis through activation of the AKT and ERK1/2 pathways, and the higher the expression level of Reg3α, the larger the colorectal tumor and the poorer the prognosis ( 70 ) ( Figure 3 ). The growth of colorectal cancer cells, LOVO and RKO, was markedly suppressed upon the downregulation of Reg3α ( 70 ). Reg3α promotes cancer cell cycle progression and tumorigenicity by forming RNA–DNA triple-stranded bodies with lncRNA Reg1CP and is associated with poor patient prognosis ( 71 ). Overall, Reg3α may regulate the proliferation and apoptosis of colorectal cancer cells through multiple signaling pathways. It is considered a potential pathogenic gene for colorectal cancer and is expected to be a target for treating this disease. However, Reg3α may also exert its function as a novel tumor suppressor. In a study conducted on mice, it was observed that overexpression of Reg3α led to the activation of T-cell-mediated immune response, resulting in a suppressive effect on colon adenocarcinoma. Additionally, analysis of clinical data revealed a positive correlation between higher levels of Reg3α expression and improved prognosis among patients diagnosed with colorectal cancer ( 72 ). The examination of human gastric cancer cell culture revealed that the promotion of tumor suppressor gene expression by Reg3α could potentially impede the proliferation of gastric cancer cells ( 73 ). Such inconsistent results of Reg3α may be due to different research objects or may be caused by differences in the selected pathological types of cancer cells, which need further research and exploration in the future. To conclude, the role of Reg3α in cancer conditions is contradictory: in some studies, it can promote the proliferation of cancer cells, but some studies have also found that Reg3α may be a new type of tumor suppressor factor. Future research on Reg3α may be a new idea for cancer treatment. Reg3β, a lectin, has also recently been found to be involved in the development of colorectal cancer. STAT3 is an important immunomodulatory factor, which plays a significant pathogenic part in colorectal cancer development, progression, and metastasis ( 74 ). In the mouse model of colorectal cancer, it was found that Reg3β could prevent colorectal cancer tumorigenesis and growth through its inhibitory effect on STAT3, and the expression of Reg3β was negatively related to the prognosis of colorectal cancer ( 75 ) ( Figure 3 ). Increasing Reg3β expression in colorectal cancer could be a promising therapeutic strategy. Reg4 is highly upregulated in gastrointestinal malignancy. REG4 expression was significantly associated with a poorer overall survival rate and recurrence-free survival rate according to the amount of substrate ( 76 ). Li et al. ( 77 ) conducted immunohistochemical studies on colorectal cancer tissues, adjacent tissues, non-adjacent tissues, and adenoma tissues. They observed an upregulation of Reg4 expression in adjacent and adenoma tissues, while a decrease was noted in colorectal cancer tissues. These findings suggest that Reg4 overexpression may be an early event in colorectal carcinogenesis. Additionally, CD44 is recognized as a marker for tumor stem cells with its intracytoplasmic domain (CD44ICD) playing an essential part in cancer cell migration and proliferation ( 78 ). Bishnupuri et al. ( 79 ) ( Figure 3 ) discovered that through its interaction with the CD44 receptor and subsequent induction of proteolysis, Reg4 can enhance the expression of the intracytoplasmic domain of CD44 (CD44ICD), thereby activating transcription of type D cyclin involved in regulating cancer cell proliferation. This ultimately promotes both colorectal cancer cell proliferation and stem cell formation. The correlation observed between Reg4 and CD44 or CD44ICD suggests that Reg4 may contribute to the enhancement of colorectal cancer cell proliferation and stem cell generation ( 80 ). KRAS is a common mutant oncogene in colorectal cancer ( 81 ). Hwang et al. ( 82 ) ( Figure 3 ) found that mutant KRAS-induced Reg4 promotes colorectal cancer stem cell formation via the Wnt/β-catenin pathway. Recently, an engineered immunoglobulin (scFv-Reg4) was generated which can bind specifically to Reg4 and block its biological activity, significantly inhibiting cancer cell proliferation ( 83 ). These findings indicate that Reg4 could potentially play a role in the initiation and progression of colorectal tumors. In the future, it is anticipated that Reg4 may serve as a valuable biomarker for predicting the prognosis of colorectal cancer. Additionally, targeting Reg4 at the molecular level holds promise for gene therapy approaches in treating colorectal cancer. 5-FU is a chemotherapy drug commonly used in the treatment of colorectal cancer; however, resistance to 5-FU chemotherapy results in the failure of colorectal cancer treatment. Previous research has demonstrated that lipid droplet accumulation contributes to chemoresistance in colorectal cancer cells ( 84 ). Zhang and his team recently discovered that Reg4 enhances chemoresistance in colorectal cancer by suppressing the transcription of ACC1 or ACLY, thereby impacting lipid droplet synthesis and assembly ( 85 ). The scFv-Reg4 significantly enhances the apoptotic effect of 5-FU, thereby indicating its potential as a promising supplement for the treatment of gastrointestinal tumors ( 83 ). The above shows that knockdown of the Reg4 gene can enhance the sensitivity of colorectal cancer to chemotherapeutic drugs, suggesting that the prognosis of colorectal cancer patients can be improved by gene knockdown. The expression of Reg4 is downregulated in chemoradiotherapy-sensitive colorectal cancer cells ( 86 ). It suggests that Reg4 may be a potential biomarker of sensitivity to radiotherapy in colorectal cancer and could help predict treatment response in patients undergoing RCT, thus enabling effective personalized treatment. In brief, the involvement of the Reg protein in gastrointestinal malignant tumors is significant, suggesting its potential as a valuable biomarker for tumor diagnosis, prognosis, and targeted therapy. In forthcoming research, targeting the Reg protein could be explored to impede tumor growth, hinder proliferation, and overcome drug resistance.

Inflammatory bowel disease (IBD), an idiopathic inflammatory disease of the intestines with clinical manifestations of diarrhea, abdominal pain, and even bloody stools, includes Crohn’s disease and ulcerative colitis and involves the ileum, rectum, and colon ( 1 ). In the 21st century, IBD has become a widespread ailment that is on the rise in both developed and developing countries. A regression analysis showed that the age-standardized prevalence of IBD in 2019 was 15.42% in Africa, 59.25% in Asia, and 147.82% in Europe, showing a significant upward trend, and the increasing global burden of IBD will pose a huge challenge to healthcare systems around the world ( 2 , 3 ). IBD is a chronic progressive disease, with the majority of patients experiencing recurrent disease flares over the course of a long illness, reducing quality of life and increasing the incidence of psychological problems significantly ( 4 ). In addition, long-term chronic inflammation in the gut can induce DNA damage through oxidative stress, leading to the activation of pro-oncogenes and inactivation of oncogenes, which ultimately heightens the susceptibility of patients to develop colorectal cancer ( 5 ). A complete understanding of the causes and development of IBD remains elusive, potentially arising from a complex interplay between factors including immune response, genetic predisposition, environmental influences, and microbiota ( 6 ). There is an increasing amount of evidence indicating that the disruption of the gut microbiota’s ecological balance serves as a catalyst for IBD ( 7 ). Disruption of the mucosal barrier caused by ecological dysregulation results in the persistence of inflammatory and carcinogenic effects. The presence of specific harmful bacteria, such as Escherichia coli and enterotoxigenic Bacteroides fragilis , can trigger the release of proinflammatory and oncogenic substances, thereby increasing the susceptibility to colorectal cancer among individuals with IBD ( 8 ). The gastrointestinal tract, being the body’s largest defense system, plays a vital role in defending against potential pathogens from entering the body; the dysfunction of the immune system within the intestines is also a significant contributing factor to the development of IBD ( 9 ). The Reg protein family was first detected in pancreatic islet cells in 1988 ( 10 ). Since its identification, Reg has been proven to be associated with various health conditions including diabetes, inflammation of the gastrointestinal tract, and cancer ( 11 ). An increasing amount of evidence indicates that the expression of Reg is considerably elevated in the gastrointestinal tract of individuals with IBD, and it possesses antibacterial properties, anti-inflammatory effects, and tissue-healing capabilities ( 12 ). In addition, the expression of the Reg protein family has been observed in cancer and shown to impact prognosis. These proteins have potential applications as diagnostic markers or therapeutic targets for gastrointestinal tumors ( 13 ). This paper examines the possible contribution of the Reg protein family to the advancement and evolution of inflammatory bowel disease and colorectal cancer, foreseeing their potential as therapeutic targets and prognostic biomarkers in future applications.

The pathogenesis of inflammatory bowel disease remains elusive, involving the intricate interplay of environmental, genetic, immune, microbial, and other factors. Dysbiosis of the intestinal microbiota disrupts intestinal homeostasis and facilitates the onset and progression of IBD. Currently, clinical management primarily relies on aminosalicylates and immunosuppressants. However, prolonged medication usage is associated with heightened adverse reactions and imposes substantial time and economic burdens on patients. In addition, chronic inflammation of the intestinal tract increases the risk of colorectal cancer, so new targets need to be found to improve patient care. The Reg protein family is involved in the regulation of intestinal flora and plays an important role in the development and treatment of inflammatory bowel disease and colorectal cancer, and in the future, through an in-depth study of the relationship between Reg proteins and gastrointestinal inflammation and malignant tumors, we can further explore the signaling pathway that regulates the expression of Reg proteins to develop relevant drugs to achieve therapeutic goals.