Distinct expression of C4.4A in colorectal cancer detected by different antibodies

GPAA1 promotes gastric cancer progression via upregulation of GPI-anchored protein and enhancement of ERBB signalling pathway

Background

Gastric cancer is one of the deadliest malignant tumours, with a high incidence in China, and is regulated by aberrantly overexpressed oncogenes. However, existing therapies are insufficient to meet patients’ needs; thus, the identification of additional therapeutic targets and exploration of the underlying mechanism are urgently needed. GPAA1 is the subunit of the GPI transamidase that transfers the GPI anchor to proteins within the ER. The functional impacts of increased expression levels of GPAA1 in human cancers are not well understood.

Methods

Data mining was performed to determine the pattern of GPAA1 expression and the reason for its overexpression in tumour and adjacent normal tissues. In vitro and in vivo experiments evaluating proliferation and metastasis were performed using cells with stable deletion or overexpression of GPAA1. A tissue microarray established by the Ren Ji Hospital was utilized to analyse the expression profile of GPAA1 and its correlation with prognosis. Western blotting, an in situ proximity ligation assay, and co-immunoprecipitation (co-IP) were performed to reveal the mechanism of GPAA1 in gastric cancer.

Results

GPAA1 was a markedly upregulated oncogene in gastric cancer due to chromosomal amplification. GPAA1 overexpression was confirmed in specimens from the Ren Ji cohort and was associated with ERBB2 expression, predicting unsatisfactory patient outcomes. Aberrantly upregulated GPAA1 dramatically contributed to cancer growth and metastasis in in vitro and in vivo studies. Mechanistically, GPAA1 enhanced the levels of metastasis-associated GPI-anchored proteins to increase tumour metastasis and intensified lipid raft formation, which consequently promoted the interaction between EGFR and ERBB2 as well as downstream pro-proliferative signalling.

Conclusions

GPAA1 facilitates the expression of cancer-related GPI-anchored proteins and supplies a more robust platform—the lipid raft—to promote EGFR-ERBB2 dimerization, which further contributes to tumour growth and metastasis and to cancer progression. GPAA1 could be a promising diagnostic biomarker and therapeutic target for gastric cancer.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1218-8) contains supplementary material, which is available to authorized users.

Expression of C4.4A is a potential independent prognostic factor for patients with gastric cancer

C4.4A, a metastasis-associated gene, encodes a glycolipid-anchored membrane protein which is overexpressed in several human malignancies. However, there are few data available on C4.4A expression and its relationship with progression in gastric cancer. Our study was designed to explore the expression of C4.4A in gastric cancer and to correlate it with clinical outcome. C4.4A expression was studied by quantitative real-time RT-PCR and immunohistochemistry for assessment of correlations with clinicopathological factors. C4.4A mRNA expression was significantly up-regulated in gastric cancer as compared with noncancerous tissue (p<0.05)., being observed in 107 (88.4%) of the 121 gastric cancer cases by immunohistochemistry. We found that the expression of C4.4A mRNA was correlated with size of the tumor, depth of invasion, lymph node metastasis, distant metastasis and TNM stage. Moreover, patients with overexpression of C4.4A has a significantly worse survival (p<0.05). Further multivariable analysis indicated that the expression of C4.4A was an independent prognostic indicator for gastric cancer (p<0.05). In conclusion, overexpression of C4.4A correlates with metastatic potential of gastric cancer and C4.4A could be a novel independent prognostic marker for predicting outcome.

Concurrent expression of C4.4A and Tenascin-C in tumor cells relates to poor prognosis of esophageal squamous cell carcinoma

C4.4A is a glycolipid-anchored membrane protein expressed in several human malignancies. We recently found that C4.4A expression was associated with poor prognosis of esophageal squamous carcinoma cells (ESCCs), but the underlying mechanism is unknown. To uncover this, we performed PCR array analysis using the HCT116 cell line, a positive control for C4.4A expression and we found that Tenascin-C (TNC) among the many adhesion molecules and extracellular matrix proteins was the best candidate for C4.4A molecule induction. Based on in vitro studies using the TE8 esophageal cancer cells, we examined by immunohistochemistry TNC expression in 111 ESCCs. We found that the TNC-positive group (24.3%) had significantly poorer prognosis than the TNC-negative group in 5-year overall survival. We also found there was a significant correlation between TNC and C4.4A in ESCC tissues (P=0.007). Finally, we found that only the double-positive group for C4.4A and TNC had a significantly worse prognosis (P=0.005). Our data suggest that TNC expression in ESCC may in part explain why C4.4A is associated with a poor prognosis of ESCC since TNC can promote invasion and metastasis.

C4.4A expression is associated with a poor prognosis of esophageal squamous cell carcinoma

BACKGROUND

C4.4A is a glycolipid-anchored membrane protein expressed in several human malignancies. We examined clinical relevance of C4.4A expression in 111 esophageal squamous cell carcinoma (ESCC) tissue samples.

METHODS

Anti-human C4.4A antibody that recognizes the glycosylphosphatidyl inositol (GPI) anchor signaling sequence (C4.4A-GPI Ab) and anti-human C4.4A-119 polyclonal antibody (C4.4A-119 Ab) were used for immunohistochemistry and Western blot testing.

RESULTS

Both antibodies detected the C4.4A protein expression at the parabasal layer of normal epithelium of the esophagus. In tumor tissues, the C4.4A protein was detected in 66 (59.5 %) and 95 (85.6 %) of 111 ESCCs by the C4.4A-GPI Ab and the C4.4A-119 Ab, respectively. The C4.4A-GPI Ab mainly detected membranous C4.4A expression (83.3 %, 55 of 66 positive cases), while the C4.4A-119 Ab exclusively detected cytoplasmic C4.4A expression (100 %, 73 cytoplasm alone and 22 cytoplasm plus membrane in 95 positive cases). Western blot analysis indicated that normal epithelium expressed the band of C4.4A at 70 kDa, whereas the tumor tissues displayed the band at the lower molecular weight. Survival analysis indicated that the C4.4A-positive ESCCs had significantly worse 5-year overall survival than the C4.4A-negative ESCC samples (P = 0.021) when using the C4.4A-GPI Ab, but not when using the C4.4A-119 Ab. This difference was most evident with membranous expression of C4.4A (P = 0.005).

CONCLUSIONS

C4.4A expression was associated with a poor prognosis of ESCC when the GPI-related antibody was used. On the other hand, the C4.4A-119 Ab may be a useful diagnostic tool for ESCC because of its high detection rate.