Identifying novel regulators of Rho1 signaling in S.cerevisiae

Rho GTPases are conserved signaling molecules that regulate a wide range of cellular pathways. Numerous regulators and effectors of Rho contribute to the complexity of Rho signaling in cells. Changes in Rho mediated pathways can often lead to human diseases, including cancer and neurodegenerative disorders. How Rho signaling specificity is regulated is not well understood. Our study uses the model organism Saccharomyces cerevisiae to study the regulation of Rho1 signaling. Rho1, the homolog of mammalian RhoA, is a monomeric Rho GTPase that regulates multiple pathways to collectively contribute to cell wall biogenesis. More than fifteen upstream regulators and downstream effectors have been characterized to mediate Rho1 signaling. A genome wide screen was previously conducted in our lab to identify novel regulators of chitin synthase 3 (Chs3) trafficking by measuring the level of chitin at the cell surface. Rho1 signaling has been implicated in the expression and post translational trafficking of Chs3 via the cell wall integrity (CWI) pathway. Not surprisingly, the top hits from the screen included known regulators of the CWI pathway. The screen also uncovered a new component of the CWI pathway, the putative ORF ADC2. Adc2 was physically associated with the RhoGEF Tus1, but not Rom2. It contributed to the localization of Tus1 at the bud neck. Adc2 was also functionally associated with Tus1 in regulating Rho1 signaling. The function of Tus1, but not Rom2, appeared to be dependent on Adc2. Overall, this study identified Adc2 as a novel regulator of Rho1 signaling. Understanding its specific affinity for Tus1 but not Rom2 may offer insights into the signaling specificity of Rho1. The discovery of Adc2 also raises awareness that additional accessory proteins may be associated with Rho signaling not only in yeast but in humans as well.Medicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat