The PfAP2-HS transcription factor protects malaria parasites from febrile temperatures

Abstract

Periodic fever is the most characteristic clinical feature of human malaria1-3, but how parasites survive febrile episodes is not known. While Plasmodium spp. genomes encode a full complement of chaperones4, they lack an ortholog of the conserved transcription factor HSF1, which in most eukaryotes activates the expression of key chaperones upon heat shock (HS)5-8. Here we identified PfAP2-HS, a transcription factor of the ApiAP2 family9-11, as the key regulator of the P. falciparum protective HS response. The PfAP2-HS-dependent HS response is largely restricted to rapid activation of hsp70-1, the predominant direct target of PfAP2-HS, and hsp90. Deletion of PfAP2-HS dramatically reduced HS survival and also resulted in severe growth defects at 37°C, but not at 35°C, and increased sensitivity to imbalances in protein homeostasis (proteostasis) produced by artemisinin, the current frontline antimalarial drug12,13. These results demonstrate that PfAP2-HS contributes to general maintenance of proteostasis and drives a rapid chaperone-based protective response against febrile temperatures. While several ApiAP2 transcription factors regulate life cycle transitions in malaria parasites11,14,15, PfAP2-HS is the first identified Plasmodium transcription factor that controls a protective response to a within-host environmental challenge.

Identification of Antimalarial Compounds that Inhibit Apicomplexan AP2 Proteins

“…To assess whether DNA binding competition was specific to the AP2-EXP AP2 domain, we repeated competitive EMSAs with three different purified P. falciparum AP2 domains: AP2-I Domain 3 (AP2-I D3) 25,32 (Fig S3B) , AP2-HS Domain 1 (AP2-HS D1) 25,36 (Fig S3C) , and PfSIP2 Domain 1 (PfSIP2 D1) 35 (Fig S3D) , again using the minimum amount of protein needed to visualize binding of each ApiAP2 protein’s cognate DNA oligonucleotide (Table S2) . AP2-I D3 32 and PfSIP2 D1 35 are essential for the IDC, while ap2-hs deletion is tolerated when parasites are grown below physiological temperatures 36 . We found that Compounds A, B, C, and I can compete DNA binding by AP2-I (Fig S4A) , Compounds B and I compete DNA binding by AP2- HS D1 (Fig S4B) and Compounds B, C and I compete DNA binding by PfSIP2 D1 (Fig S4C) .…”

“…These docking simulations resulted in a final list of S2). AP2-I D3 32 and PfSIP2 D1 35 are essential for the IDC, while ap2-hs deletion is tolerated when parasites are grown below physiological temperatures 36 S3. )…”

“…In the rodent malaria model species P. berghei 30 and P. yoelii 31 , 11 ApiAP2 proteins have developmental lethal phenotypes in the sexual blood or mosquito stages. ApiAP2 transcription factors can cause activation or repression of transcription of specific genes, and they are involved in diverse lifecycle processes including invasion, mutually exclusive antigenic gene expression, sexual differentiation, and heat stress tolerance 27,[32][33][34][35][36][37][38][39][40] . Chromatin interacting proteins such as histone deacetylases and methyltransferases have received recent attention as potential drug targets against malaria parasites 41,42 .…”