Role of protein kinase A in Trypanosoma cruzi

Protein kinase A (PKA) is an important mediator of many signal transduction pathways that occur in eukaryotic cells, and it has been implicated as a regulator of stage differentiation in Trypanosoma cruzi. To evaluate the importance of the PKA catalytic subunit of T. cruzi (TcPKAc), a gene encoding a PKA inhibitor (PKI) containing a specific PKA pseudosubstrate, R-R-N-A, was subcloned into a pTREX vector and introduced into epimastigotes by electroporation. Expression of PKI has a lethal effect in this parasite. Similarly, a pharmacological inhibitor, H89, killed epimastigotes at a concentration of 10 mu M. To understand the biology of PKA, identification of the particular substrates of this enzyme is essential. Using a yeast two-hybrid system, 38 candidates interacting with TcPKAc were identified. Eighteen of these were hypothetical proteins with unknown functions, while the others had putative or known functions. The entire open reading frames of eight genes presumably important in regulating T. cruzi growth, adaptation, and differentiation, including a type III PI3 kinase (Vps34), a putative PI3 kinase, a putative mitogenactivated extracellular signal-regulated kinase, a cyclic AMP (cAMP)-specific phosphodiesterase (PDEC2), a hexokinase, a putative ATPase, a DNA excision repair protein, and an aquaporin were confirmed to interact with TcPKAc in the yeast Saccharomyces cerevisiae under the highest stringency selection conditions, and PKA phosphorylated the recombinant proteins of these genes. Taken together, these findings demonstrate the importance of cAMP-PKA signaling in this organism.