Inhibition of plant plasma membrane phosphoinositide phospholipase C by the actin‐binding protein, profilin

Abstract

A key event in signal transduction in many eukaryotes is activation of polyphosphoinositide‐specific phospholipase C (PIC). This enzyme hydrolyses the plasma membrane‐associated lipid, phosphatidylinositol(4,5)bisphosphate (Ptdlns(4,5)P2) which leads to the production of the two second messenger molecules: inositol(1,4,5)trisphosphate (Ins(1,4,5)P3) and 1,2‐diacylglycerol (DG). In plants, an enzyme which functionally resembles mammalian PIC is known to exist in the plasma membrane, but little is understood about how its activity is regulated. The recent discovery of several plant proteins with 30–40% homology to the mammalian actin‐ and phosphoinositide‐binding protein, profilin, has prompted an investigation as to whether these proteins (plant profilins) are able to interact with polyphosphoinositides and, if so, whether such interactions have physiological relevance for signal transduction via the plant phosphoinositide system. In this study it is demonstrated that a direct and highly specific interaction does exist between plant profilin and polyphosphoinositides and that these interactions dramatically affect the ability of plant plasma membrane phosphoinositide phospholipase C to utilize phosphoinositides for second messenger production. These data are the first to demonstrate a functional role of plant profilin in controlling polyphosphoinositide turnover and also provide the first evidence for a direct effect of an actin‐binding protein on a membrane‐associated signalling enzyme. These findings indicate a novel mechanism for control of plant phosphoinositide turnover, and suggest a possible link between plant cell activation, second messenger production and modulation of cytoskeletal dynamics.

Identification and characterization of a low temperature regulated gene encoding an actin‐binding protein from wheat

“…Cofilin was found to inhibit phospholipase C activity by protecting PIP2 from hydrolysis, suggesting that the cytoskeleton participates in signal transduction processes in a cofilin-dependent manner [4]. A similar result was obtained with another actin binding protein, profilin, which was found to bind PIPz and inhibit phospholipase C in bean leaf plasma membrane [16]. In C. communis, disruption of actin organization impairs the ability of the stomata to respond to environmental cues.…”

Impacts of Aluminum on the Cytoskeleton of the Maize Root Apex. Short-Term Effects on the Distal Part of the Transition Zone1

“…Later, provided evidence of a direct Almediated inhibition of phospholipase C and hypothesized that the phosphoinositide-signaling pathway might be the initial target of Al. In accordance with this hypothesis, components of the actin-based cytoskeleton were found to directly interact with phospholipase C (Huang et al, 1998), a crucial enzyme in the plant phosphoinositide signaling cascade and even to regulate its activity (Drøbak et al, 1994).…”

Maize Profilin Isoforms Are Functionally Distinct

“…The inhibition of bean (Vicia faba) plasma membrane phosphoinositide phospholipase C activity by the maize profilins was measured as described previously (Drøbak et al, 1994). Briefly, phosphoinositidase activity was assayed by incubating bean plasma membranes at 25ЊC in 50 L of buffer E (50 mM Tris/malate, pH 6.0, and 10 M CaCl 2 ) with 50 M phosphatidylinositol-4,5-bisphosphate (PtdIns[4,5]P 2 ) and 0.86 kBq 3 H-PtdIns(4,5)P 2 , in the presence of 0.0, 1.4, 2.8, 5.7, or 14.2 M recombinant ZmPRO1, ZmPRO5, or human profilin I.…”