Neuroendocrine differentiation: a risk fellow in colorectal cancer

Abstract

Background: Neuroendocrine differentiation (NED) is often found in colorectal cancer (CRC) and may have unique biological behavior, which has not been previously delineated. Here, we explore the relationship between CRC, NED, and clinicopathological factors. We also offer a preliminary explanation of the mechanism underlying the malignant biological behavior of NED in CRC.

Methods: Between 2013 and 2015, 394 CRC patients who underwent radical operations were selected for analysis. The relationship between NED and clinicopathological factors was analyzed. To further clarify the pivotal role of NED in CRC, we performed bioinformatic analyses and identified genes that may be involved in NED, which were obtained from in silico data from The Cancer Genome Atlas (TCGA) database. Then, we conducted functional enrichment analyses and confirmed the critical pathways for intensive study. Moreover, we detected the expression of key proteins by immunohistochemistry and analyzed the correlation of their expression with NED.

Results: The statistical analysis showed that CRC with NED was positively correlated with lymph node metastasis. Through bioinformatic analysis, we found that chromogranin A (CgA) was positively correlated with invasion and lymph node metastasis. ErbB2 and PIK3R1, which are key proteins in the PI3K-Akt signaling pathway, were closely related to NED. Furthermore, we determined that the PI3K-Akt signaling pathway likely plays a critical role in the NED of CRC.

Conclusions: CRC with NED is associated with lymph node metastasis. The PI3K-Akt signaling pathway, which is closely related to CRC, may be the mechanism promoting the malignant biological behavior of CRC with NED.

Keywords: Colorectal cancer; Lymph node metastasis; Neuroendocrine differentiation; PI3K-Akt signaling pathway.

Fig. 1

A Neuroendocrine tumor cells in CRC detected by immunostaining for CgA (magnification x 100). B Neuroendocrine tumor cells in CRC detected by immunostaining for SYP (magnification x 100). C Relative expression of CgA in CRC and corresponding non-cancerous tissues from TCGA. ***P < 0.001. D Relative expression of SYP in CRC and corresponding non-cancerous tissues from TCGA. ***P < 0.001. E Kaplan–Meier curve analysis of the correlation of CgA expression and overall survival or progression-free survival from TCGA. F Kaplan–Meier curve analysis of the correlation of SYP expression and overall survival or progression-free survival from TCGA. CgA, chromogranin A; CRC, colorectal cancer; SYP, synaptophysin; TCGA, The Cancer Genome Atlas

Fig. 2

The correlation between CgA and SYP expression and pTNM stage of CRC. A The analyses of CgA expression in pT1+T2 stage and pT3+T4 stage. B The analyses of CgA expression in pN0 stage and pN1+N2 stage. C The analyses of CgA expression in pM0 stage and pM1 stage. D The analyses of SYP expression in pT1+T2 stage and pT3+T4 stage. E The analyses of SYP expression in pN0 stage and pN1+N2 stage. F The analyses of SYP expression in pM0 stage and pM1 stage. CgA, chromogranin A; CRC, colorectal cancer; SYP, synaptophysin

Fig. 3

Heatmap of DEGs between upregulation and downregulation of CgA or SYP. A Heatmap of the top 25 DEGs between upregulation and downregulation of CgA (log2 FC > 2, P < 0.01). B Heatmap of the top 25 DEGs between upregulation and downregulation of SYP (log2 FC > 2, P < 0.01). The left vertical axis shows clusters of DEGs and right vertical axis represents gene names. Red represents upregulated genes and blue represents downregulated genes. CgA, chromogranin A; DEGs, differentially expressed genes; FC, fold change; SYP, synaptophysin

Fig. 4

KEGG pathway enrichment network diagram for DEGs. A KEGG pathways enrichment analysis of CgA. B KEGG pathways enrichment analysis of SYP. “Count” represents the number of genes. CgA, chromogranin A; DEGs, differentially expressed genes; KEGG, Kyoto Encyclopedia of Genes and Genomes; SYP, synaptophysin

Fig. 5

The Venn diagram of intersection analysis of consensus genes. The cluster of genes were respectively from differentially expressed genes of CgA and SYP, and the genes enriched in “PI3K-Akt signaling pathway”. CgA, chromogranin A; SYP, synaptophysin

Fig. 6

Immunohistochemical staining of key proteins in the PI3K-Akt signaling pathway. A ErbB2-positive and negative staining (magnification x 100). First row, positive; second row, negative. B PIK3R1-positive and negative staining (magnification x 100). First row, positive; second row, negative

Fig. 7

CRC with NED releases neuroendocrine granules which act on surrounding CRC cells through paracrine secretion, thus activating the PI3K-AKT signaling pathway and causing tumor invasion and metastasis. CRC, colorectal cancer; NED, neuroendocrine differentiation