Secretory Mucin 5AC Promotes Neoplastic Progression by Augmenting KLF4-Mediated Pancreatic Cancer Cell Stemness

Abstract

Secreted mucin 5AC (MUC5AC) is the most abundantly overexpressed member of the mucin family during early pancreatic intraepithelial neoplasia stage I (PanIN-I) of pancreatic cancer. To comprehend the contribution of Muc5ac in pancreatic cancer pathology, we genetically ablated it in an autochthonous murine model (KrasG12D; Pdx-1cre, KC), which mirrors the early stages of pancreatic cancer development. Neoplastic onset and the PanIN lesion progression were significantly delayed in Muc5ac knockout (KrasG12D; Pdx-1 cre; Muc5ac−/−, KCM) animals with a 50% reduction in PanIN-2 and 70% reduction in PanIN-3 lesions compared with KC at 50 weeks of age. High-throughput RNA-sequencing analysis from pancreatic tissues of KCM animals revealed a significant decrease in cancer stem cell (CSC) markers Aldh1a1, Klf4, EpCAM, and CD133. Furthermore, the silencing of MUC5AC in human pancreatic cancer cells reduced their tumorigenic propensity, as indicated by a significant decline in tumor formation frequency by limiting dilution assay upon subcutaneous administration. The contribution of MUC5AC in CSC maintenance was corroborated by a significant decrease in tumor burden upon orthotopic implantation of MUC5AC-depleted pancreatic cancer cells. Mechanistically, MUC5AC potentiated oncogenic signaling through integrin αvβ5, pSrc (Y416), and pSTAT3 (Y705). Phosphorylated STAT3, in turn, upregulated Klf4 expression, thereby enriching the self-renewing CSC population. A strong positive correlation of Muc5ac with Klf4 and pSTAT3 in the PanIN lesions of KC mouse pancreas reinforces the crucial involvement of MUC5AC in bolstering the CSC-associated tumorigenic properties of Kras-induced metaplastic cells, which leads to pancreatic cancer onset and progression. Significance: This study elucidates that de novo expression of MUC5AC promotes cancer cell stemness during Kras-driven pancreatic tumorigenesis and can be targeted for development of a novel therapeutic regimen.

Atypical Mucin Expression Predicts Worse Overall Survival in Resectable Pancreatic Ductal Adenocarcinoma

“…Paradoxically, MUC2 has increased expression level in certain types of gastrointestinal malignancies 21,27 , which denotes that MUC2 may also be employed by cancer cells and function as mucous barrier against anti-tumour immune reaction. MUC5 is another secreted mucin and promotes KLF4 mediated PDAC cancerous stemness 9 . In addition, CA19-9, the most commonly used prognostic marker for pancreatic cancerous disease, is present on the surface of MUC1 and MUC5 20,28 ; With respect to the recent discovery that CA19-9 bolsters PDAC initiation and progression 29 , the interaction between mucins and CA19-9 suggests that mucins are not merely prognostic factors but also participate in the onset and advancement of PDAC.…”

“…MUC2 is secreted to form insoluble mucous gel barrier and generally identi ed as a tumour suppressor 8 , both normal pancreatic tissue and PDAC rarely have a positive expression of MUC2. Another gel forming mucin MUC5, on the contrary, is abundantly overexpressed in PDAC tissues and potentiates oncogenic signalling pathway 9 . Correspondingly, these aberrantly glycosylated mucins can be recognized as tumour associated antigens, which could be employed as useful predictors for the effectiveness of adjuvant therapy 10,11 and potential targets for cancer therapy 12 .…”

“…Mucin expression pattern is altered throughout the progression and metastasis of PDAC 9,15 , and MUC1 positive, MUC2 negative and MUC5 positive have been considered as the typical mucin expression pattern of PDAC 16,17 . However, there still exists a subgroup with atypical mucin expression pattern who comprise approximately 20 to 30 percent of PDAC patients, and prior studies have inconsistent conclusions about the association between mucin expression and PDAC patients' survival.…”

Abnormal Glycosylation of Cancer Stem Cells and Targeting Strategies

“…For example, GALNT-6 elevated mucin-O-glycosylation of a2M, which activates downstream PI3/Akt signaling pathway, fosters metastasis of breast cancer (69). CD44+, CD24+ and CD133+ CSC populations of pancreatic cancer also express Mucin-1 (115) and Mucin 5AC also plays significant role in maintaining stemness properties of pancreatic CSC (116). Increased fraction of CD44+, CD24-CSC and Mucin-1 expression was also reported in breast cancer MCF-7 cells when exposed to tumor associated macrophages (117).…”

MUC14-Related ncRNA-mRNA Network in Breast Cancer

“…Increasing evidences have suggested that all the three subgroups' MUC members are closely linked to cancer initiation and progression. For example, Ganguly et al found that secretory MUC5AC promoted neoplastic progression by augmenting KLF4-mediated pancreatic cancer cell stemness [7]; Xu et al indicated that MUC1 was overexpressed in NSCLC and silence of MUC1 alleviated paclitaxel resistance of NSCLC [8]; Gao et al suggested that MUC12 enhanced RCC progression by regulating c-Jun/TGF-β signaling [9]; Tiemin et al found that MUC13 facilitated progression of intrahepatic cholangiocarcinoma via EGFR/PI3K/AKT pathways [10]. Moreover, dysregulated MUCs are reported to serve as potential biomarkers in multiple tumor types.…”