A protein in crude cytosol regulates glucose-6-phosphatase activity in crude microsomes to regulate group size in Dictyostelium

Wonhee Jang, Richard H. Gomer

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Dictyostelium discoideum form groups of ∼2 × 104 cells. The group size is regulated in part by a negative feedback pathway mediated by a secreted multipolypeptide complex called counting factor (CF). The CF signal transduction pathway involves CF-repressing internal glucose levels by increasing the Km of glucose-6-phosphatase. Little is known about how this enzyme is regulated. Glucose-6-phosphatase is associated with microsomes in both Dictyostelium and mammals. We find that the activity of glucose-6-phosphatase in crude microsomes from cells with high, normal, or low CF activity had a negative correlation with the amount of CF present in these cell lines. In crude cytosols (supernatants from ultracentrifugation of cell lysates), the glucose-6-phosphatase activity had a positive correlation with CF accumulation. The crude cytosols were further fractionated into a fraction containing molecules greater than 10 kDa (S > 10K) and molecules less than 10 KDa (S < 10K). S > 10K from wild-type cells strongly repressed the activity of glucose-6-phosphatase in wild-type microsomes, whereas S > 10K from countin- cells (cells with low CF activity) significantly increased the activity of glucose-6-phosphatase in wild-type microsomes by decreasing Km. The regulatory activities in the wild-type and countin- S > 10Ks are heat-labile and protease-sensitive, suggesting that they are proteins. S < 10K from both wild-type and countin- cells did not significantly change glucose-6-phosphatase activity. Together, the data suggest that, as a part of a pathway modulating multicellular group size, CF regulates one or more proteins greater than 10 KDa in crude cytosol that affect microsome-associated glucose-6-phosphatase activity.

Original languageEnglish
Pages (from-to)16377-16383
Number of pages7
JournalJournal of Biological Chemistry
Volume281
Issue number24
DOIs
StatePublished - 16 Jun 2006

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