Uses GRA16 To Upregulate Host c-Myc.

Manipulation of the host cell is a crucial part of life for many intracellular organisms. We have recently come to appreciate the extent to which the intracellular pathogen reprograms its host cell, and this is illustrated by the marked upregulation of the central regulator c-Myc, an oncogene that coordinates myriad cellular functions. In an effort to identify an effector protein capable of regulating c-Myc, our laboratory constructed a screen for mutant parasites unable to accomplish this upregulation. Interestingly, this screen identified numerous components of a complex located in/on the parasitophorous vacuole membrane necessary to translocate proteins out into the host cytosol, but it never identified a specific effector protein. Thus, how the parasite upregulates c-Myc has largely been a mystery. Previously, the dense granule protein GRA16 has been described to bind to one isoform of PP2A-B, a regulatory subunit that coordinates the activity of the catalytic protein phosphatase PP2A. As other PP2A subunits have been reported to target PP2A protein phosphatase activity to c-Myc, subsequently leading to c-Myc destabilization, we examined whether GRA16 has an impact on host c-Myc accumulation. Expression of 's GRA16 protein in , a close relative of that does not naturally upregulate host c-Myc, conferred the ability on to do this now. Further support was obtained by deleting the gene from and observing a severely diminished ability of tachyzoites to upregulate host c-Myc. Thus, GRA16 is an effector protein central to 's ability to upregulate host c-Myc. The proto-oncogene c- plays a crucial role in the growth and division of many animal cells. Previous studies have identified an active upregulation of c-Myc by tachyzoites, suggesting the existence of one or more exported "effector" proteins. The identity of such an effector, however, has not previously been known. Here, we show that a previously known secreted protein, GRA16, plays a crucial role in c-Myc upregulation. This finding will enable further dissection of the precise mechanism and role of c-Myc upregulation in -infected cells.