ABSTRACT
A sphingolipid metabolite regulator, sphingosine kinase 1 (SPHK1), plays a critical role in the development of colorectal cancer (CRC). Studies have demonstrated that invasion and metastasis of CRC are promoted by SPHK1-driven autophagy. However, the exact mechanism of SPHK1 drives autophagy to promote tumor progression remains unclear. Here, immunohistochemical detection showed the expression of SPHK1 and tumor necrosis factor receptor-associated factor-6 (TRAF6) in human CRC tissues was stronger than in adjacent normal tissues, they were both associated with distance metastasis. It was discovered that knockdown of SPHK1 reduced the expression of TRAF6, inhibited autophagy, and inhibited the growth and metastasis of CRC cells in vitro. Moreover, the effects of SPHK1-downregulating were reversed by overexpression of TRAF6 in CRC cells transfected by double-gene. Overexpression of SPHK1 and TRAF6 promoted the expression of autophagy protein LC3 and Vimentin, while downregulated the expression of autophagy protein P62 and E-cadherin. The expression of autophagy-related ubiquitination protein ULK1 and Ubiquitin protein were significantly upregulated in TRAF6-overexpressed CRC cells. In addition, autophagy inhibitor 3-methyladenine (3MA) significantly inhibited the metastasis-promoting effect of SPHK1 and TRAF6, suppressed the expression of LC3 and Vimentin, and promoted the expression of P62 and E-cadherin, in CRC cells. Immunofluorescence staining showed SPHK1 and TRAF6 were co-localized in HT29 CRC cell membrane and cytoplasm. Immunoprecipitation detection showed SPHK1 was efficiently combined with the endogenous TRAF6, and the interaction was also detected reciprocally. Additionally, proteasome inhibitor MG132 treatment upregulated the expression of TRAF6 and the level of Ubiquitin protein, in SPHK1-downregulating CRC cells. These results reveal that SPHK1 potentiates CRC progression and metastasis via regulating autophagy mediated by TRAF6-induced ULK1 ubiquitination. SPHK1-TRAF6-ULK1 signaling axis is critical to the progression of CRC and provides a new strategy for the therapeutic control of CRC.
Subject(s)
Colorectal Neoplasms , Phosphotransferases (Alcohol Group Acceptor) , TNF Receptor-Associated Factor 6 , Humans , Autophagy/physiology , Autophagy-Related Protein-1 Homolog/genetics , Autophagy-Related Protein-1 Homolog/metabolism , Cadherins/metabolism , Cell Line, Tumor , Colorectal Neoplasms/pathology , Intracellular Signaling Peptides and Proteins/metabolism , TNF Receptor-Associated Factor 6/genetics , TNF Receptor-Associated Factor 6/metabolism , Ubiquitination , Ubiquitins/metabolism , VimentinABSTRACT
It's well known that N6-methyladenosine (m6A) modification is the most abundant modification in multiple RNA species. miRNAs play important roles in m6A modification and are closely related with occurrence and development of colorectal cancer (CRC). Thus, the aim of this study was to identify the prognostic value of m6A-related miRNAs and explore the correlation between the miRNAs and immune microenvironment in CRC. The differentially expressed m6A regulators and differentially expressed miRNAs between CRC tissues and adjacent normal tissues were identified based on TCGA dataset, and the m6A-related miRNAs were screened. The CRC patients from TCGA were randomized (1:1) into training set and validation set, and the risk score was established in the training set. Next, risk score was verified in the validation set and GSE92928 from GEO datasets. Besides, the relationship among tumor mutational burden, immune microenvironment and risk score were analyzed. What's more, RT-qPCR were used to explore the expression levels of the miRNAs in risk score between SW480 and SW620. A total of 29 m6A-related miRNAs were screened out, and a 5-differentially expressed miRNAs risk score was established. Kaplan-Meier analysis and ROC curves revealed the risk score could predict the prognosis of CRC, accurately. Similarly, the patients in the high-risk group had shorter overall survival in GSE92928. The risk score was relevant with the tumor mutational burden and immune infiltration, and the expression of HAVCR2 was significant difference between 2 risk groups. The expression levels of miR-328-3p, miR-3934-5p, miR-664b-5p and miR-3677-3p were down-regulated in SW620 compared with SW480, only the expression level of miR-200c-5p was up-regulated in SW620. The findings provided the new insights into the correlation between miRNAs and m6A regulators. The m6A-related miRNAs could predict the prognosis of CRC and provide the valuable information of immunotherapy in CRC patients.
