Role of Cdc42-Cla4 Interaction in the Pheromone Response of Saccharomyces cerevisiae

Abstract

In Saccharomyces cerevisiae, the highly conserved Rho-type GTPase Cdc42 is essential for cell division and controls cellular development during mating and invasive growth. The role of Cdc42 in mating has been controversial, but a number of previous studies suggest that the GTPase controls the mitogen-activated protein (MAP) kinase cascade by activating the p21-activated protein kinase (PAK) Ste20. To further explore the role of Cdc42 in pheromone-stimulated signaling, we isolated novel alleles of CDC42 that confer resistance to pheromone. We find that in CDC42(V36A) and CDC42(V36A, I182T) mutant strains, the inability to undergo pheromone-induced cell cycle arrest correlates with reduced phosphorylation of the mating MAP kinases Fus3 and Kss1 and with a decrease in mating efficiency. Furthermore, Cdc42(V36A) and Cdc42(V36A, I182T) proteins show reduced interaction with the PAK Cla4 but not with Ste20. We also show that deletion of CLA4 in a CDC42(V36A, I182T) mutant strain suppresses pheromone resistance and that overexpression of CLA4 interferes with pheromone-induced cell cycle arrest and MAP kinase phosphorylation in CDC42 wild-type strains. Our data indicate that Cla4 has the potential to act as a negative regulator of the mating pathway and that this function of the PAK might be under control of Cdc42. In conclusion, our study suggests that control of pheromone signaling by Cdc42 not only depends on Ste20 but also involves interaction of the GTPase with Cla4.

p21-Activated Kinases Cla4 and Ste20 Regulate Vacuole Inheritance in Saccharomyces cerevisiae

“…Cla4 and Ste20 play many unique and overlapping roles in the cell (35,45). We therefore hypothesized that STE20-overexpressing cells might also have a vacuole inheritance defect.…”

Yeast and fungal morphogenesis from an evolutionary perspective

“…The major role for Ste20 during these processes is to transmit signal input at the plasma membrane to the MAP kinase cascades that leads to transcriptional activation of the downstream morphogenetic programs. Whereas Ste20 has its own set of interacting partners promoting these processes, Cla4 appears to have a negative effect on the pheromone response [104], further indicating functional divergence of these homologous kinases.…”

Role of Hsl7 in Morphology and Pathogenicity and Its Interaction with Other Signaling Components in the Plant Pathogen Ustilago maydis

“…Cla4 regulates septin function and polarized growth, as well as cytokinesis (5). Data have linked Ste20 to cell polarity and cytokinesis, Cla4 to the mating response, and both to actin organization, indicating that a functional overlap between the two kinases exists (21,25,30). In S. pombe, Shk1 (Ste20 homologue) is essential for viability and is required for several cell functions, including mating, cytoskeletal regulation, cell cycle regulation, and response to hyperosmotic conditions, while Shk2 (Cla4 homologue), dispensable for growth, appears to be redundant to Shk1in many functions (4,40,49).…”

“…They are involved in a myriad of cellular functions, including cell cycle regulation, cytoskeletal organization, mating responses, cell polarity, morphogenesis, and separation, and responses to environmental conditions (7,21,22,31,41). Homologues of the PAK family are known to activate the mitogen-activated protein kinase (MAPK) pathway (17,30).…”