Anoikis is known as a specific type of programmed cell death, apoptosis caused by loss of cell adhesion or inappropriate cell adhesion. Dysplastic cell growth or cells attached to inappropriate substrates can be effectively removed by anoikis, thereby maintaining tissue homeostasis and development. However, during tumorigenesis, cancer cells often acquire resistance to anoikis and become more aggressive and metastatic, making anoikis a potential prognostic and therapeutic target for cancer(Malagobadan, Ho, & Nagoor, 2020). In endometrial cancer, novel ARGs signatures have been identified to predict prognosis(S. Chen, Gu, Zhang, Hu, & Ge, 2021). However, the role of ARGs in PAAD has not been elucidated, and our study aimed to elucidate this role.
We first elucidated the screening for pancreatic anoikis-related genes and their prognostic value. We found that the expression of BRMS1, PTK2, BCL2L11, SRC, CEACAM6, CAV1, ITGB1, CEACAM5, EGFR, BCL2, CASP8, PTRH2, STAT3, CTNNB1, ZNF304, MAPK1, BMF, ITGA5, TP53, MCL1, BCL2L1, CASP3, and CDH1 was increased in PAAD compared with normal tissues.
Prognostic analysis showed that pancreatic patients with high expression of PTK2, ITGB1, EGFR, CASP8, BCL2L1, and CASP3 had a lower survival rate. These data are consistent with previous results. Hayato Fujita et al. found that EGFR mRNA expression may help predict the prognosis and sensitivity of PDAC patients to gemcitabine(Fujita et al., 2011). We also performed a functional enrichment analysis of ARGs and found that these 23 ARGs are mainly involved in proteoglycans in cancer, regulation of anoikis, lipid and atherosclerosis, focal adhesion, regulation of apoptotic signaling pathway, EGFR tyrosine kinase inhibitor resistance, and human cytomegalovirus infection. Interestingly, these functions or pathways are involved in pancreatic carcinogenesis and progression. In addition, a previous study showed that Inhibition of focal adhesion kinase (FAK) alters the production of pro-inflammatory and immunosuppressive cytokines by pancreatic cancer cells and impairs their ability to avoid immune surveillance(H. Jiang et al., 2016). These results suggest that these 23 ARGs may also play an important role in the tumorigenesis and progression of PAAD.
LASSO Cox regression analysis was used to construct a prognostic genetic model based on six prognostic ARGs (PTK2, ITGB1, EGFR, CASP8, BCL2L1, and CASP3), which predicted overall survival of pancreatic patients with moderate to high precision. The predictive nomogram shows that overall survival at 1- and 2- year can be predicted relatively well compared to the ideal model in the entire cohort. A previous study identified several ferroptosis-related prognostic features in pancreatic cancer and validated the potential value of ferroptosis-related prognostic features in the personalized immunotherapy of pancreatic cancer(P. Jiang et al., 2021). It has been found that CD73 can be used as a prognostic marker that can promote pancreatic cancer progression as well as achieve immune escape by disrupting T-cell infiltration and immune response, which ultimately leads to poor prognosis(Q. Chen et al., 2020). In addition, a prognostic signature was constructed based on immune-related genes in pancreatic cancer, which showed better ability to predict 1-, 2- and 3-year survival in pancreatic cancer patients(Liu, Fu, He, Du, & Xu, 2021). In our study, we identified for the first time a prognostic gene signature associated with anoikis of pancreatic cancer, which provides additional options for prognostic prediction of Pancreatic.
In our study, PTK2 was found to be one of the gene signatures. A previous study showed that PTK2 regulates cell cycle progression and plays an important role in cell proliferation and apoptosis. PTK2, also known as focal adhesion kinase 1, regulates cell migration and adhesion and is significantly associated with loss-of-nest apoptosis, thus being involved in cancer development and progression(Weisser et al., 2014; Zachary, 1997). In addition, the causal role of PTK2 in tumor development and its association with poor clinical outcome, PTK2 may be a useful target for tumor therapy(McLean et al., 2005). However, studies on the role of PTK2 in anoikis in pancreatic cancer are limited. In our study, we found that PTK2 is one of the prognostic biomarkers associated with anoikis in PAAD. We need to perform further in vivo and in vitro studies to verify whether PTK2 is involved in anoikis in pancreatic cancer.
Another important finding of our study showed that the above prognostic genes associated with anoikis were significantly associated with immune infiltration, which further supports the fact that anoikis plays an important role in the tumor immune microenvironment. Interleukin-8 expression was found to be negatively associated with anoikis in colorectal cancer cells(Xiao et al., 2015). Anti-GD2 ganglioside antibodies can induce anoikis in cancer cells and thus treat human small cell lung cancer(Aixinjueluo et al., 2005). EGFR regulates the immune microenvironment of pancreatic cancer tumors, and its inhibitor erlotinib has been approved by the FDA for the treatment of pancreatic cancer(Li et al., 2021). Recently, ITGB1 has been identified as a potential biomarker for predicting gastric cancer patients who may benefit from immune checkpoint inhibitors(Gu et al., 2022). TMB is considered a potential biomarker for predicting the effect of immunotherapy.
Our findings identified BCL2L1 as an independent risk factor for pancreatic cancer, while in past studies, BCL2L1 was found to promote the growth of colon cancer cells. However, we further explored the expression of BCL2L1 in pancreatic cancer cells and human normal pancreatic ductal epithelial cell and found that the expression of BCL2L1 in pancreatic cancer cells was significantly higher than that in human normal pancreatic ductal epithelial cells, and we constructed an interference plasmid for BCL2L1 and found that knocking down the expression of BCL2L1 in pancreatic cancer cells could inhibit the proliferation ability of the cells by CCK-8 assay.
We also investigated the relationship between six prognostic ARGs and tumor mutational load, and microsatellite instability. Tumor mutational load (TMB), microsatellite instability (MSI) are current biomarkers of cancer immunotherapy effectiveness and are clinically important for patients with a wide range of solid tumors(Addeo, Friedlaender, Banna, & Weiss, 2021; Cortes-Ciriano, Lee, Park, Kim, & Park, 2017). Our final results showed that only the expression of CASP8, BCL2L1 and CASP3 correlated with TMB analysis.