MicroRNA-mediated dysregulation of host-cell signalling pathways in HPV-driven cervical cancers

Persistent infection of high-risk human papillomaviruses (HPVs) is the causal factor
of >99% of cervical malignancies, and an increasing proportion of oropharyngeal
carcinomas. HPV-associated transformation is driven by the viral oncoproteins E6
and E7, which dysregulate a range of host-cell signalling pathways. As there are
currently no available targeted treatments for HPV malignancies, a comprehensive
understanding of the dysregulated signalling pathways manipulated by HPV is
required. One way in which E6 and E7 disrupt cell signalling is through regulation of
host microRNAs (miRNAs). Previous work in the Macdonald group identified that the
oncogenic miR-18a is upregulated in HPV+ cervical cancers and drives cell
proliferation and survival through directly targeting the tumour suppressive STK4, a
major upstream component of the Hippo signalling pathway. However, the full
extent to which miR-18a contributes to cervical cancer cell phenotype is yet to be
revealed.
Predicted miR-18a targets were integrated with publicly available cervical cancer
gene expression datasets to uncover biologically significant miR-18a target
interactions. These analyses identified three novel miR-18a target interactions that
contribute to cell proliferation in cervical cancer cell lines. Inhibition of miR-18a
resulted in the de-repression of RASAL2, TGFBR3, and CSRNP3, and overexpression
of each of these genes impeded HeLa cell proliferation. Luciferase reporter assays
confirmed miR-18a targeting of the predicted seed-binding regions within the 3′ UTR
of these genes. Notably, CSRNP3 was significantly downregulated in HPV+ cervical
cancer cell lines, and high-grade CIN samples, and its expression is regulated by
HPV16 and HPV18 oncogenes. Overexpression of CSRNP3 induced a G1 phase cell
cycle arrest and activated apoptotic signalling, delaying cell proliferation. Finally, IP-
MS identified three potential CSRNP3-protein interactions which could contribute
to CSRNP3 tumour suppressive function. Further research is warranted to elucidate the
mechanisms underlying CSRNP3-mediated apoptosis and to determine the
implications of its DNA-binding ability.