Uncovering the Signaling Networks of Sit4, a PP2A-like Phosphatase Required for Brain Infection of Cryptococcus neoformans
Soojin Yu, Yeseul Choi, Yujin Lee, and Yong-Sun Bahn*
Department of Biotechnology, College of Life Science and Biotechnology, Yonsei University, Seoul, Korea
*Email of corresponding author: firstname.lastname@example.org
Phosphatases play critical roles in regulating cellular signaling networks involved in the survival and virulence of fungal pathogens. Specifically, protein phosphatase 2A (PP2A) is a highly conserved and abundant serine-threonine phosphatase composed of catalytic, scaffold, and regulatory subunits. In this study, we aim to unravel the signaling networks of a PP2A-like phosphatase SIT4 in Cryptococcus neoformans, an opportunistic fungal pathogen that causes fatal meningoencephalitis. From a previous systematic analysis, we have identified SIT4 as a virulence-related phosphatase that promotes blood-brain barrier adhesion and crossing. To elucidate the factors involved in the regulation of SIT4, a red-fluorescent fusion protein was constructed for pull-down assay, through which one putative regulatory subunit, SAP190 (SIT4-associating protein 190), was identified. As SIT4 is downstream of the TOR (target of rapamycin) pathway, both sit4∆ and sap190∆ displayed increased susceptibility against rapamycin. The loss of the SAP190 gene also showed reduced BBB crossing but at a reduced severity compared to sit4∆, while virulence was not affected. Moreover, because the TOR pathway regulates cell growth and metabolic status, the expression of SIT4 and SAP190 under glucose starvation condition was observed. As a result, the expression of both SIT4 and SAP190 increased in the wild type strain under glucose starvation. Surprisingly, in basal condition, SIT4 transcription increased in sap190∆ while SAP190 transcription increased in sit4∆ at a level higher than the wild type. From here, we aim to identify the signaling networks of SIT4 to uncover its role and mechanism in brain infection.