Cells were lysed in RLT buffer (Qiagen) supplemented with β-mercaptoethanol, homogenized by QIAshredder (Qiagen), and kept in a -80 °C freezer until further processing. Total RNA was isolated on the EZ1 Advanced XL (Qiagen) automated RNA purification instrument using the EZ1 RNA Cell Mini Kit (Qiagen) following the manufacturer's protocol, including an on-column DNase digestion. Sequencing libraries were prepared using the Illumina Stranded mRNA Prep, Ligation kit (San Diego, CA) following protocols provided by the manufacturer.