MSI1 suppresses hyperactive RAS via the cAMP-dependent protein kinase and independently of chromatin assembly factor-1

Abstract

RAS hyperactivation in the yeast Saccharomyces cerevisiae leads to multiple nutritional growth defects associated with overstimulation of the cAMP signaling pathway. Hyperactive RAS can be suppressed by overexpression of MSI1, a subunit of chromatin assembly factor-1 (yCAF-1). MSI1 overexpression suppresses phenotypes induced by increased cAMP content in multiple genetic backgrounds. However, MSI1 does not inhibit cAMP synthesis or total cellular cAMP-dependent protein kinase (PKA) activity, nor does MSI1 stimulate expression of several cAMP-repressible genes critical for the acquisition of thermotolerance in the stationary phase. Our analysis indicates that yCAF-1 is dispensable for inhibition of hyperactive RAS by MSI1. We demonstrate that in the presence of the PKA regulatory subunit, BCY1, MSI1 inhibits phenotypes of a mutationally activated PKA catalytic subunit. These observations indicate that MSI1 affects PKA function in a BCY1-dependent manner via mechanisms other than direct overall inhibition of PKA catalytic activity. MSI1 appears to provide two distinct roles in chromatin modeling as a component of yCAF-1, and in the inhibition of RAS signaling by modulating PKA.

CAC3 (MSI1) Suppression ofRAS2G19V Is Independent of Chromatin Assembly Factor I and Mediated by NPR1

“…1) in a CAF-I independent manner (Fig. 2), a result consistent with a recent report (51). Because CAC3 acts antagonistically with the Sin3p-Rpd3p complex (42) and the mammalian Cac3p homolog (RbAp48) is associated with chromatin-modifying enzymes such as histone deacetylases and histone acetylases (43,49), we asked if the CAC3 suppression of RAS2 G19V required histone-modifying activities such as the G19V -induced heat shock sensitivity.…”

“…However, CAC3 overexpression did not affect the total level of extractable PKA kinase activity. Their data indicated that CAC3 suppressed the RAS/cAMP pathway in a CAC1-independent and BCY1-dependent fashion which is not fully understood (51). The results presented here support and extend their conclusions by indicating that Npr1p is the target of Cac3p that modulates the RAS/cAMP signal transduction pathway.…”

“Sleeping Beauty”: Quiescence inSaccharomyces cerevisiae

“…This Ccr4p-Not complex may mediate the repression of Msn2p and Msn4p by the PKA pathway. The PKA pathway may also alter chromatin structure (184). Finally, the PKA pathway has recently been shown to be a direct activator of pyruvate kinase (Cdc19p) (126) and Cox6p (176) in proliferating cells, suggesting a possible role for the pathway in regulating carbohydrate metabolism and mitochondrial function at the diauxic shift.…”

Glucose Signaling in Saccharomyces cerevisiae

“…The Ras/cAMP/PKA pathway has also been implicated in aging (212,216), thermotolerance (439), bud site selection, actin repolarization (333), glycogen accumulation (342), stress resistance (39,407), and sporulation (39,41); it may also regulate pseudohyphal differentiation (growth as chain-like multicellular filaments) in response to nutrient limitation. Each of these interesting topics (see reference 411 for a recent review), as well as the involvement in these processes of other nutrientstimulated kinases (e.g., Snf1 and TOR [45,75,196,197,401,441]), GTPases (e.g., Gpa2 [277]), and transcription factors (e.g., Msn2/Msn4 [30,96,112]), is outside the scope of this review.…”