Background
Integrin subunit α 8 (ITGA8) methylation has been associated with the development of several cancers, but its contribution to breast cancer remains unclear. The present study aimed to investigate the methylation status of ITGA8, and the underlying regulatory mechanisms of ITGA8 methylation in breast cancer.
Conclusions
Low ITGA8 expression in ER-positive breast cancer might be caused by the hypermethylation of ITGA8, a process dependent on ERα. Our findings provide an important foundation for investigations into ITGA8-targeted treatment strategies for ER-positive breast cancer.
Methods
ITGA8 expression was investigated using the Gene Expression Profiling Interactive Analysis 2 (GEPIA2) database and the Breast Cancer Gene-Expression Miner v.4.4 (bc-GenExMiner v4.4). The association between ITGA8 expression levels and the survival rate of breast cancer patients was evaluated using The Cancer Genome Atlas (TCGA) database and Gene Expression-based Outcome for Breast Cancer Online (GOBO): Gene Set Analysis. Methylation-specific PCR (MSP) was used to detect the methylation of ITGA8. Protein level of ITGA8 was determined by Western blot analysis.
Results
ITGA8 was expressed at low levels in human breast cancer cells compared to non-tumorigenic breast cells and breast tissue, and was upregulated in estrogen receptor (ER)-positive tissue compared with ER-negative tissue (P<0.01). ITGA8 gene expression was negatively associated with breast tumor stage and survival rate in all breast cancer patients. However, ER-positive patients with low ITGA8 expression showed poorer distant metastasis-free survival (DMFS) and recurrence-free survival (RFS) rates than patients with high ITGA8 expression. This was not observed in the ER-negative population. Mechanistically speaking, hypermethylation of ITGA8 was discovered in ER-positive breast cancer cells. Administration of the methylation inhibitor, 5-aza-2'-deoxycytidine (5-aza-dC), significantly elevated protein expression of ITGA8 in ER-positive breast cancer cells compared to ER-negative cells. The positive association between ITGA8 status and methylation was also observed in clinical tissue specimens. When treated with 17-beta-estradiol, an antagonist of ERα, 5-aza-dC-induced upregulation of ITGA8 in ER-positive breast cancer cells was no longer observed. Conclusions: Low ITGA8 expression in ER-positive breast cancer might be caused by the hypermethylation of ITGA8, a process dependent on ERα. Our findings provide an important foundation for investigations into ITGA8-targeted treatment strategies for ER-positive breast cancer.