TY - JOUR
T1 - A protein in crude cytosol regulates glucose-6-phosphatase activity in crude microsomes to regulate group size in Dictyostelium
AU - Jang, Wonhee
AU - Gomer, Richard H.
PY - 2006/6/16
Y1 - 2006/6/16
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=33745186025&partnerID=8YFLogxK
U2 - 10.1074/jbc.M509995200
DO - 10.1074/jbc.M509995200
M3 - Article
C2 - 16606621
AN - SCOPUS:33745186025
SN - 0021-9258
VL - 281
SP - 16377
EP - 16383
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 24
ER -