Liver-specific protein 2: a Plasmodium protein exported to the hepatocyte cytoplasm and required for merozoite formation.

The liver stage is the first stage of the malaria parasite that replicates in the vertebrate host. However, little is known about the interplay between the parasite liver stage and its host cell, the hepatocyte. In this study, we identified an exported protein that has a critical role in parasite development in host hepatocytes. Expressed sequence tag analysis of Plasmodium berghei liver-stage parasites indicated that transcripts encoding a protein with an N-terminal signal peptide, designated liver-specific protein 2 (LISP2), are highly expressed in this stage. Expression of LISP2 was first observed 24 h after infection and rapidly increased during the liver-stage schizogony. Immunofluorescent staining with anti-LSP2 antibodies showed that LISP2 was carried to the parasitophorous vacuole and subsequently transported to the cytoplasm and nucleus of host hepatocytes. Gene targeting experiments demonstrated that majority of the LISP2-mutant liver-stage parasites arrested their development during formation of merozoites. These results indicate that exported LISP2 is involved in parasite-host interactions required for the development of liver-stage parasites inside hepatocytes. This study demonstrated that mid-to-late liver-stage malarial parasites have a system for exporting proteins to the host cell as intraerythrocytic stages do and presumably to use the proteins to modify the host cell and improve the environment.