Overexpression and cytoplasmic accumulation of Hepl is associated with clinicopathological parameters and poor prognosis in non-small cell lung cancer

The Lung Adenocarcinoma Microenvironment Mining and Its Prognostic Merit

Background:

As a common pathological type of lung cancer, lung adenocarcinoma (LUAD) is mainly treated by surgery, chemotherapy, targeted therapy and radiotherapy. Although a relatively mature treatment system has been established, there are few studies on the microenvironment of LUAD.

Material and Methods:

The immune and stromal scores of patients from the LUAD cohort in the TCGA database were obtained by using ESTIMATE. The relationship of immune and stromal scores with the clinicopathological characteristics and overall survival of LUAD patients was assessed by R. GO, KEGG and Cox regression analyses were employed to analyze intersecting genes and to identify reliable prognostic markers. The identified genes were also analyzed in the GEPIA database to assess their correlations with survival, and these relationships were verified with the Kaplan-Meier Plotter database.

Results:

The immune score was related to the survival time and tumor topography of LUAD patients. There was a significant correlation between stromal score and tumor metastasis. Through multivariate analysis, stage (HR = 1.640, 95% CI = 1.019-2.642, P = 0.042) and risk score (HR = 1.036, 95% CI = 1.026-1.046, P < 0.001). The genes (ARHGAP15, BTLA, CASS4, CLECL1, FAM129C, STAP1, TESPA1, and S100P) showed credible prognostic value in LUAD patients in TCGA through GEPIA database online analysis and verification in the Kaplan-Meier plotter database.

Conclusions:

In the microenvironment of lung adenocarcinoma, the differentially expressed genes screened by immune score and stromal score have certain value in evaluating the survival/prognosis of patients, as well as the invasion and progression of tumors.

Overexpression of CASS4 promotes invasion in non-small cell lung cancer by activating the AKT signaling pathway and inhibiting E-cadherin expression

The role of Crk-associated substrate (CAS) family members in regulating invasion and metastasis has been described in several cancers. As the fourth member of the CAS family, CASS4 is also related with positive lymph node metastasis and poor prognosis in lung cancer. However, the underlying mechanisms and downstream effectors of CASS4 in the development and progression of non-small cell lung cancer (NSCLC) remain unclear. In this study, CASS4 overexpression inhibited E-cadherin expression and enhanced invasion in NSCLC cell line transfected with CASS4 plasmid, while CASS4 depletion upregulated E-cadherin expression and inhibited invasion in NSCLC cell line transfected with CASS4 siRNA. The effect of CASS4 overexpression in facilitating invasion of NSCLC cells was reversed by restoring E-cadherin expression, which indicates that CASS4 may promote invasion by inhibiting E-cadherin expression. Subsequent immunohistochemistry results confirmed that CASS4 overexpression correlated with loss of E-cadherin expression. We next investigated the phosphorylation levels of focal adhesion kinase (FAK), p38, extracellular signal-related kinase (ERK), and AKT after CASS4 plasmid or CASS4 siRNA transfection. CASS4 facilitated AKT (Ser473) phosphorylation. Treatment with an AKT phosphorylation inhibitor reversed the increased invasive capacity and downregulation of E-cadherin protein induced by CASS4 overexpression. Taken together, the present results indicate that CASS4 may promote NSCLC invasion by activating the AKT signaling pathway, thereby inhibiting E-cadherin expression.

Embryonal Fyn-associated substrate (EFS) and CASS4: The lesser-known CAS protein family members

The CAS (Crk-associated substrate) adaptor protein family consists of four members: CASS1/BCAR1/p130Cas, CASS2/NEDD9/HEF1/Cas-L, CASS3/EFS/Sin and CASS4/HEPL. While CAS proteins lack enzymatic activity, they contain specific recognition and binding sites for assembly of larger signaling complexes that are essential for cell proliferation, survival, migration, and other processes. All family members are intermediates in integrin-dependent signaling pathways mediated at focal adhesions, and associate with FAK and SRC family kinases to activate downstream effectors regulating the actin cytoskeleton. Most studies of CAS proteins to date have been focused on the first two members, BCAR1 and NEDD9, with altered expression of these proteins now appreciated as influencing disease development and prognosis for cancer and other serious pathological conditions. For these family members, additional mechanisms of action have been defined in receptor tyrosine kinase (RTK) signaling, estrogen receptor signaling or cell cycle progression, involving discrete partner proteins such as SHC, NSP proteins, or AURKA. By contrast, EFS and CASS4 have been less studied, although structure-function analyses indicate they conserve many elements with the better-known family members. Intriguingly, a number of recent studies have implicated these proteins in immune system function, and the pathogenesis of developmental disorders, autoimmune disorders including Crohn's disease, Alzheimer's disease, cancer and other diseases. In this review, we summarize the current understanding of EFS and CASS4 protein function in the context of the larger CAS family group.

CAS proteins in health and disease: an update

The CAS family of scaffolding proteins has increasingly attracted scrutiny as important for regulation of cancer-associated signaling. BCAR1 (also known as p130Cas), NEDD9 (HEF1, Cas-L), EFS (Sin), and CASS4 (HEPL) are regulated by and mediate cell attachment, growth factor, and chemokine signaling. Altered expression and activity of CAS proteins are now known to promote metastasis and drug resistance in cancer, influence normal development, and contribute to the pathogenesis of heart and pulmonary disease. In this article, we provide an update on recently published studies describing signals regulating and regulated by CAS proteins, and evidence for biological activity of CAS proteins in normal development, cancer, and other pathological conditions.