Phagocytosis is required for transduction of cholesterol signaling in Tetrahymena thermophila.

HERNANDEZ J; UTTARO AD; GARCIA SIBURU, N; FREA, V

Buenos Aires

Congreso; LIII Reunión anual de la SAIB; 2017

PHAGOCYTOSIS IS REQUIRED FOR TRANSDUCTION OF CHOLESTEROL SIGNALING IN TETRAHYMENA THERMOPHILAT. thermophila synthesizes the triterpenoid tetrahymanol instead of sterols. The presence of exogenous cholesterol is sensed by the ciliate, triggering several physiological processes: cell motility increases immediately, cholesterol is taken up and converted to 7,22 bisdehydrocholesterol (bDHC), the synthesis of tetrahymanol is repressed and the triterpenoid is replaced by bDHC in the ciliate membranes. Cholesterol uptake appears to proceed exclusively via phagocytosis, as previously determined by using fluorescent analogues. Here we show that, in presence of cholesterol, genes involved in the synthesis of bDHC and putatively in sterol uptake, were transcriptionally up-regulated whereas that of the tetrahymanol synthesis were down-regulated. It was revealed after the analysis of a differential transcriptome and confirmed by RT-qPCR. Using a T. thermophila thermosensitive mutant, defective only in phagocytosis (strain II8G), we found a drastic reduction of cholesterol uptake and a negligible bioconversion to bDHC at the restrictive temperature (37°C) when compared to the wild type strain under the same conditions. RT-qPCR carried out on the mutant strain grown at 30°C in the presence or absence of cholesterol, showed similar up- or down-regulation of the genes as described above, but not significant regulation was detected at the restrictive temperature. It indicates that cells need to be competent for phagocytosis, not only to incorporate cholesterol, but also to sense its presence and to transduce the signal to the macronucleus.Keywords: sterols, signaling, transduction, phagocytosis, ciliates