MicroRNAs (miRNAs) are small non-coding RNAs that can play critical roles in regulating various cellular processes including during many parasitic infections. Here, we report a regulatory role for miR-34c-3p in cAMP-independent regulation of PKA activity in Theileria annulata and Plasmodium falciparum infections of bovine leukocytes and human erythrocytes, respectively. We identified prkar2b (cAMP-dependent protein kinase A type II-beta regulatory subunit), as a novel miR-34c-3p target gene and demonstrated how infection-induced up-regulation of miR-34c-3p in leukocytes repressed PRKAR2B expression to increase PKA activity and promote the virulent disseminating tumour phenotype of T. annulata-transformed macrophages. When human erythrocytes are infected by P. falciparum they accumulate miR-34c-3p that ablates both prkar2b and parasite Pfpkar mRNA. However, erythrocytes lack protein translation machinery so only miR-34c-3p-mediated loss of Pfpkar transcripts results in an increase in PfPKA kinase activity. Inhibition of miR-34c-3p increases Pfpkar expression to reduce PfPKA activity leading to slowing of intra-erythrocyte parasite development and a reduction in invasion of fresh red blood cells. Finally, we demonstrate that miR-34c-3p regulation of prkar2b expression is generalizable, by showing that it can negatively regulate prkar2b expression and PRKAR2B protein levels in human cancer cell lines and that brown adipose tissue displays high levels of miR-34c-3p and corresponding low levels of prkar2b mRNA compared to white adipose tissue. Induction of miR-34c-3p therefore, represents a novel cAMP-independent way of regulating PKA activity in a range of cell types associated with cancer, diabetes and parasitic diseases.### Competing Interest StatementThe authors have declared no competing interest.

miR-34c-3p regulates PKA activity independent of cAMP via ablation of PRKAR2B in Theileria annulata-infected leukocytes and Plasmodium falciparum-infected erythrocytes