PCBP1 and PCBP2 both bind heavily oxidized RNA but cause opposing outcomes, suppressing or increasing apoptosis under oxidative conditions.

PCBP1, a member of the poly(C)-binding protein (PCBP) family, has the capability of binding heavily oxidized RNA and therefore participates in the cellular response to oxidative conditions, helping to induce apoptosis. There are four other members of this family, PCBP2, PCBP3, PCBP4 and hnRNPK, but it is not known whether they play similar roles. To learn more, we first tested their affinity for an RNA strand carrying two 8-oxoguanine (8-oxoG) residues at sites located in close proximity to each other, representative of a heavily oxidized strand, or RNA with one 8-oxoG, or none. Among them, only PCBP2 exhibited highly selective binding to RNA carrying two 8-oxoG residues similar to that observed with PCBP1. In contrast, PCBP3, PCBP4 and hnRNPK bound RNA with or without 8-oxoG modifications and exhibited slightly increased binding to the former. Mutations in conserved RNA-binding domains of PCBP2 disrupted the specific interaction with heavily oxidized RNA. We next tested PCBP2 activity in cells. Compared to wild-type HeLa S3 cells, PCBP2-KO cells established by gene editing exhibited increased apoptosis with increased caspase 3 activity and PARP1 cleavage under oxidative conditions, which were suppressed by the expression of wild-type PCBP2 but not one of the mutants lacking binding activity. In contrast, PCBP1-KO cells exhibited reduced apoptosis with much less caspase 3 activity and PARP cleavage than wild-type cells. Our results indicate that PCBP2, as well as PCBP1, bind heavily oxidized RNA; however, the former may counteract PCBP1 to suppress apoptosis under oxidative conditions.