Breast cancer is an aggressive malignancy with high morbidity in females 
worldwide. Extensive studies reveal that long noncoding RNAs (lncRNAs) are 
abnormally expressed and act as key regulators in various cancers, including 
breast cancer. In this work, we investigated the role and regulatory mechanism 
of lncRNA prostate cancer-associated transcript 6 (PCAT6) in breast cancer 
progression. Our findings revealed that PCAT6 was overexpressed in breast cancer 
tissues and cell lines. Furthermore, elevation of PCAT6 reflected an adverse 
prognosis of patients. Functional experiments indicated that PCAT6 knockdown 
hampered cell proliferation, facilitated apoptosis and cell cycle arrest in 
vitro, and inhibited tumor growth in vivo. We also found that the transcription 
factor SP1 could bind to the PCAT6 promoter and promoted its expression. 
Subsequently, it was verified that PCAT6 was a molecular sponge for microRNA-326 
(miR-326), and the leucine-rich repeat containing the eight family member E 
(LRRC8E) was a direct target of miR-326. Rescue assays revealed that LRRC8E 
overexpression attenuated the suppressive effect of PCAT6 knockdown on cellular 
progression of breast cancer. In summary, this study demonstrated that 
SP1-activated PCAT6 promoted the malignant behaviors of breast cancer cells by 
regulating the miR-326/LRRC8E axis.