Mutations within the LINC-HELLP non-coding RNA differentially bind ribosomal and RNA splicing complexes and negatively affect trophoblast differentiation

LINC-HELLP, showing chromosomal linkage with the pregnancy-specific HELLP syndrome in Dutch families, reduces differentiation from a proliferative to an invasive phenotype of first-trimester extravillous trophoblasts. Here we show that mutations in LINC-HELLP identified in HELLP families negatively affect this trophoblast differentiation either by inducing proliferation rate or by causing cell cycle exit as shown by a decrease in both proliferation and invasion. As LincRNAs predominantly function through interactions with proteins, we identified the directly interacting proteins using chromatin isolation by RNA purification followed by protein mass spectrometry. We found 22 proteins predominantly clustering in two functional networks, i.e. RNA splicing and the ribosome. YBX1, PCBP1, PCBP2, RPS6 and RPL7 were validated, and binding to these proteins was influenced by the HELLP mutations carried. Finally, we show that the LINC-HELLP transcript levels are significantly upregulated in plasma of women in their first trimester of pregnancy compared with non-pregnant women, whereas this upregulation seems absent in a pilot set of patients later developing pregnancy complications, indicative of its functional significance in vivo.